LG 27GN950

Introduction

It’s been a while since we tested the first 4K @ 144Hz desktop monitor back in August 2018, when we reviewed the Asus ROG Swift PG27UQ. This provided cutting edge technology in the market and finally offered the combination of super-high resolutions and refresh rates, packed in to a 27″ sized screen. At the time there was some criticism from consumers about some of the colour sacrifices that were needed to reach the maximum 4K @ 144Hz. Those early generation screens were limited by even the most recent DisplayPort 1.4 connection bandwidth and to reach above 98Hz required a drop from 10-bit colour depth to 8-bit, and then to reach above 120Hz you had to sacrifice some colour chroma as well. In practice this wasn’t always an issue, but it put some people off. Later on some manufacturers experimented with using dual DisplayPort connections but while this avoided the need to drop colour depth and chroma for the top end refresh rates, it was restrictive in terms of using features like G-sync/FreeSync and HDR. We saw this method used with the Acer Nitro XV273K for instance in December 2018.

More recently some 4K @ 144Hz displays like the Asus ROG Strix XG27UQ which we tested in April 2020 worked around this bandwidth limitation by making use of VESA’s Display Stream Compression (DSC) technology, a visually lossless solution available from modern graphics cards that allows you to make full use of the resolution and refresh rate without needing to drop colour depth or chroma. This seemed to work very well and provides an excellent way to boost the capability of existing DisplayPort 1.4 connections for these kind of screens.

These 4K @ 144Hz screens we’ve tested in the past have all been based on AU Optronics’ IPS-type panel technology and performed very well, they were first to market with a panel of this spec and it was widely adopted. More recently LG.Display have made excellent advances in the high refresh rate IPS space with their Nano IPS technology. We’ve seen very popular models like the 27″ 27GL850 with 1440p resolution and 144Hz, 34″ 34GK950F with 3440 x 1440 resolution and 144Hz, and 37.5″ 38GL950G with 3840 x 1600 resolution and an overclocked 175Hz refresh rate appear based on their newly updated technology. LG are now venturing in to the 4K @ 144Hz space with their latest flagship model, the 27″ 27GN950. We have this with us now for testing and review.

The 27GN950 is 27″ in size with a 3840 x 2160 Ultra HD “4K” resolution. The Nano IPS panel boasts a refresh rate of 144Hz maximum (160Hz via a newly added overclocking mode) along with support for adaptive-sync, allowing for variable refresh rates from compatible AMD and NVIDIA graphics cards. The screen has also been officially certified under the NVIDIA ‘G-sync Compatible’ and AMD ‘FreeSync Premium Pro’ standards which should give assurances around its performance. The 27GN950 also has a few other other interesting features. It uses DSC for visually lossless support of high resolution and refresh rates, without the need for colour depth or chroma sacrifices. There is hardware calibration support along with a factory calibration, and it also features some modest HDR capability, conforming to the DisplayHDR 600 standard and therefore supporting some level of backlight local dimming, and the prerequisite wide gamut with 98% DCI-P3 coverage and 10-bit colour depth support quoted.

For reference we initially tested the screen with the latest available firmware installed via the OnScreen Control software, which at the time of testing was showing as (v3.03, 5.57). We also had chance to test early the new firmware from LG which fixed a couple of issues we’d identified (covered during the review) and also added support for a 160Hz overclocking mode. This was updated manually and showed as v3.06, 5.57. This new firmware should be available now for end users via LG.com and the OnScreen software.

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Specifications and Features

The following table gives detailed information about the specs of the screen as advertised:

The 27GN950 offers a reasonable range of modern connectivity with 1x DisplayPort 1.4 and 2 x HDMI 2.0 offered for video connections. There is no HDMI 2.1 offered, and that has yet to be used on any available desktop monitor. These are located on the back of the screen along with a headphone output and 2x USB downstream ports. For PC connectivity the DisplayPort is the most common option and required to support the maximum resolution and refresh rate of the screen, with HDMI being available then for connecting external games consoles or Blu-ray players potentially. The screen has an external power supply and the screen also comes packaged with the power cable and adapter that you need.

Below is a summary of the features and connections of the screen.

Design and Ergonomics

The 27GN950 comes in a mostly black design with some red trim highlights. The display has a 4 side “borderless” design with a thin 2.5mm black plastic edge, and a thin 3.5mm black panel border before the image starts around the sides and top. Along the bottom there is a slightly thicker 8.5mm black panel border. The stand is a matte black plastic colour and is thick and chunky, providing a sturdy and stable base for the display. There is some red trim on the bottom front edge of the foot as pictured above. The NVIDIA G-sync logo on the left hand side of the foot is a sticker by the way, so can be removed, whereas the LG logo on the right hand edge is etched on to the plastic finish and is permanent.

The back of the screen is encased in a matte black plastic for a simple design and in keeping with other recently tested LG screens. The stand connects in the middle and can be removed for VESA mounting if you’d prefer. The connections are quite simply to get at on the back of the screen too. You can also notice the built in cable tidy clip on the back of the stand here.

The screen includes LG’s Sphere Lighting system which can be set to a range of colours and modes through the OSD menu, a quick access scroll wheel on the bottom edge of the screen, or via the additional LG Control Center software. It provides quite a bright back lighting option behind the screen and a good range of options and modes to play with. See LG’s product pages for more information on this.

The screen has a thick and chunky stand as shown above but it is at least very stable. The stand offers tilt, height and rotate adjustments but oddly no swivel. We missed that actually as it is often useful. We aren’t sure why that was left off to be honest.

Tilt adjustment is smooth and easy to operate and provides a wide adjustment range. Height adjustment is also very smooth, maybe a little stiff moving it downwards but overall very good. At the lowest adjustment the bottom edge of the screen doesn’t sit that low, being 100mm above the desk edge. At maximum extension it is 210mm and so a total 110mm adjustment range is provided here. Rotation function is also quite smooth and easy to use if you want to use the screen in portrait mode. The screen remains very stable when making adjustments with no wobble at all thanks to the sturdy stand and design.

A summary of the ergonomic adjustments are shown below:

The materials were of a very good standard and the build quality felt good. The whole screen remained cool even during prolonged use. There is a small fan used on this screen but it’s very quiet and we didn’t even notice it in day to day use, it never seemed to get loud. If you press your ear up to the top of the screen you can hear it whirring away a little, so if you are super-sensitive to this kind of thing or have a silent PC then keep this in mind.

The OSD menu is split in to 5 sections and offers a good range of options to play with. This is controlled via a single joystick control on the bottom edge of the screen. Navigation was quick, easy and intuitive. There was also quick access to the volume control and brightness settings from this joystick which was handy.

LG provide a useful “OnScreen” software which can help you control various parts of the screen. This also includes a utility for updating the monitor firmware quickly and easily should LG ever offer updates. It’s always good to have simple user control over firmware updates for bug fixes and improvements, without needing to send the screen back to the manufacturer if something was ever identified (and evident by some of the early bugs we encountered, now fixed).

The LG Control Center software can also be installed to help you control the Sphere lighting system in more detail.

Panel and Backlighting

The backlight is controlled using a direct current (DC) method for all brightness adjustments and so is flicker-free as advertised.

  
Confirmation of flicker free backlight operation, shown above at calibrated brightness level. Horizontal scale = 5ms

Brightness and Contrast

This section tests the full range of luminance (the brightness of the screen) possible from the backlight, while changing the monitors brightness setting in the OSD menu. This allows us to measure the maximum and minimum adjustment ranges, as well as identify the recommended setting to reach a target of 120 cd/m² for comfortable day to day use in normal lighting conditions. Some users have specific requirements for a very bright display, while others like a much darker display for night time viewing or in low ambient light conditions. At each brightness level we also measure the contrast ratio produced by the screen when comparing a small white sample vs. a black sample (not unrealistic full screen white vs. full screen black tests). The contrast ratio should remain stable across the adjustment range so we also check that.

Graphics card settings were left at default with no ICC profile or calibration active. Tests were made using an X-rite i1 Display Pro Plus colorimeter. It should be noted that we used the BasICColor calibration software here to record these measurements, and so luminance at default settings may vary a little from the LaCie Blue Eye Pro report you will see in other sections of the review.

It should be noted that for these tests we disabled the ‘Smart Energy Saving’ function in the OSD menu and also turned Local Dimming off. At the full brightness setting in the OSD the maximum luminance reached a very high 465 cd/m² which was a fair bit higher even than the 400 cd/m² max brightness spec from the manufacturer in SDR mode. There was a decent 376 cd/m² adjustment range in total, so at the minimum setting you could reach down to a luminance of 90 cd/m². This was a reasonable adjustment at the lower end, and should allow you a low luminance option for working in darkened room conditions with low ambient light although it was not as low as some screens can reach. In very dark settings this might still be a little high for some people. A setting of 7 in the OSD menu is needed to return you a luminance as close to 120 cd/m² as possible at default settings.

We have plotted the luminance trend on the graph above. The screen behaves as it should in this regard, with a reduction in the luminance output of the screen controlled by the reduction in the OSD brightness setting.

The average contrast ratio of the screen was measured at 994:1 out of the box which was decent for an IPS panel and basically spot on with the 1000:1 specification. We will see if this is impacted at all by later calibration.

Testing Methodology

An important thing to consider for most users is how a screen will perform out of the box and with some basic manual adjustments. Since most users won’t have access to hardware colorimeter tools, it is important to understand how the screen is going to perform in terms of colour accuracy for the average user.

We restored our graphics card to default settings and disabled any previously active ICC profiles and gamma corrections. The screen was tested at default factory settings using our new X-rite i1 Pro 2 Spectrophotometer combined with LaCie’s Blue Eye Pro software suite. An X-rite i1 Display Pro Plus colorimeter was also used to verify the black point and contrast ratio since the i1 Pro 2 spectrophotometer is less reliable at the darker end.

Targets for these tests are as follows:

• CIE Diagram – confirms the colour space covered by the monitors backlighting in a 2D view, with the black triangle representing the displays gamut, and other reference colour spaces shown for comparison. Usually shown as a comparison against the common sRGB space
• Colour space coverage volumes – we also measure using a piece of software called ChromaPure the colour space (gamut) volumes produced by the backlight in comparison to the sRGB, DCI-P3 and Rec.2020 colour spaces. sRGB is the most commonly used colour space so it is important to have a decent coverage from the screen here. If the colour space is >100% sRGB then the screen can produce a wider colour gamut, often reaching further in to the wider gamut DCI-P3 (commonly used for HDR) and Rec.2020 reference spaces.
• Gamma – we aim for 2.2 which is the default for computer monitors
• Colour temperature / white point – we aim for 6500k which is the temperature of daylight
• Luminance – we aim for 120 cd/m², which is the recommended luminance for LCD monitors in normal lighting conditions
• Black depth – we aim for as low as possible to maximise shadow detail and to offer us the best contrast ratio
• Contrast ratio (static) – we aim for as high as possible. Any dynamic contrast ratio controls are turned off here if present
• dE average / maximum – we aim for as low as possible. If DeltaE >3, the color displayed is significantly different from the theoretical one, meaning that the difference will be perceptible to the viewer. If DeltaE <2, LaCie considers the calibration a success; there remains a slight difference, but it is barely undetectable. If DeltaE < 1, the color fidelity is excellent.

Default Performance and Setup

The 27GN950 comes with a factory calibration report as shown above with our sample. This confirms some fairly relaxed calibration measures for the screen that have been achieved as it comes out of the factory. It has a gamma somewhere between 2.1 and 2.3, a white point between 6000 – 7000k and a dE of <5. These are in our opinion a bit too relaxed, and we would have liked to have seen a bit more precision in the targets being met, along with perhaps an actual figure achieved instead of just a generic “pass”. We went on to measure the screen anyway.

Default settings of the screen were as follows:

It should be noted that for these tests we disabled the ‘Smart Energy Saving’ function in the OSD menu and also turned Local Dimming off.Initially out of the box the screen was set in the ‘Gamer1’ preset mode. The display was set with a high 80% brightness which was far too bright for general use and as with most displays will need to be turned down. Colours looked vivid and bright thanks to the wide gamut backlight but the colour balance and temperature felt good. We went ahead and measured the default state with the i1 Pro 2.The CIE diagram on the left of the image confirms that the monitors colour gamut (black triangle) extends a considerable way beyond the sRGB reference space (orange triangle), mostly in green and red shades. We measured using ChromaPure software a 132.3% sRGB gamut volume coverage which corresponds to 97.5% of the DCI-P3 reference and 70.0% of the Rec.2020 reference. This is basically spot on to the specified 98% DCI-P3 coverage. There is also an sRGB emulation mode available on this screen which we will test in a moment which should provide a way to reduce the colour gamut somewhat if you wanted to specifically work with smaller standard gamut content. The wider gamut here in the default mode with more vivid and saturated colours is nice for gaming and multimedia which is the screen’s primary target usage.

Default gamma was recorded at a 2.2 average with a minor 2% deviance from the target of 2.2 which was very good, showing a little more deviance in the lighter grey shades. The default colour temperature was a little too cool at 6858k (6% out from our target), although not too bad.

Luminance at the default 80% brightness level was recorded at 404 cd/m² which was too high for prolonged general use, you will want to turn that down a lot to something more comfortable. The black depth was measured at 0.42 cd/m² at this default brightness setting, giving us a decent 979:1 contrast ratio for an IPS panel and close to the spec. Colour accuracy measurements should be ignored here really as they are comparing the produced wider gamut display colours against an sRGB reference which will always lead to errors. There was no sign of any colour banding at default settings when testing gradients which was good news, and smooth gradation across the range.

sRGB Emulation Mode

We also entered the sRGB preset mode which we expected to offer an sRGB emulation, although we were disappointed with what this offered initially:

In this mode there is a default brightness level of 5 in the OSD, which is actually a lot more comfortable than the Gamer1 80% level. You can thankfully still adjust this if you like, it’s not locked like brightness is on many screens in the sRGB mode. Many of the other picture options are locked and unavailable though so it’s pretty inflexible beyond the brightness and contrast controls.

There were several significant problems with this mode though initially, most obviously that it didn’t actually offer any sRGB emulation at all! The colour space still extended way beyond the sRGB reference and we measured a 129.2% sRGB coverage here. This so-called emulation mode had only reduced the colour space by 3.1%! We reported this back to LG who confirmed that a new firmware would fix this issue. They gave us access to this new firmware early for additional testing and we are pleased to report it did indeed fix the problem with the emulation nicely. We re-tested the screen as below…

Thanks to the new firmware the sRGB emulation mode now correctly restricted the colour space, covering 99.8% of the sRGB reference and reducing all the over-coverage we had from the native backlight gamut.

The only other remaining problems with this mode is that the gamma is now skewed as well, measured at 2.5 here (11% deviance from our target) and without the access to the gamma control in the OSD in this mode, you can’t change it either. White point was good at 6471k, but because of the high gamma the dE measurements were off as well. We have fed this back to LG for further investigation as this could well be addressed through a firmware update we are sure.

Thankfully there is a way to have even better control and accuracy including with an emulated sRGB colour space, but you will need to be able to hardware calibrate the screen.

Optimal Settings Pre-Calibration

We also measured the screen after adjusting only the OSD controls, to obtain the optimal setup without a full calibration, and without the use of an ICC correction profile. This represents what could be achieved through just simple changes to the monitor itself, and also what you could expect when working with content outside of an ICC profile managed workflow. The early stages of our calibration software helped identity these optimal OSD settings.

For this section we switched back to the ‘Gamer1’ preset mode where the full native gamut was used. We had access to the colour temp settings and RGB controls and therefore the ability to correct the white point in this mode. We stuck with Mode2 gamma which had returned us a decent gamma curve out of the box. Brightness control was also adjusted to make the screen more comfortable.

This has helped correct the white point to 6555k and reduce the brightness to a much more comfortable level. The contrast ratio was improved a bit but remained very close to the default setup and the manufacturers spec of 1000:1. These optimal settings helped the screen look a bit better than out of the box, certainly helping with the brightness if nothing else. Further calibration and profiling below can help improve things a bit further.

Calibration

We used the X-rite i1 Pro 2 Spectrophotometer combined with the LaCie Blue Eye Pro software package to achieve these results and reports. An X-rite i1 Display Pro Plus colorimeter was used to validate the black depth and contrast ratios due to lower end limitations of the i1 Pro device.

The OSD settings were adjusted as shown in the table above, as guided during the calibration process and measurements. These OSD changes allowed us to obtain an optimal hardware starting point and setup before software level changes would be made at the graphics card level. We left the  LaCie software to calibrate to “max” brightness which would just retain the luminance of whatever brightness we’d set the screen to, and would not in any way try and alter the luminance at the graphics card level, which can reduce contrast ratio. These adjustments before profiling the screen would help preserve tonal values and limit banding issues. After this we let the software carry out the LUT adjustments and create an ICC profile.

The default gamma curve deviation of 2% had been corrected now thanks to the profiling, reaching the 2.2 average with 0% average variation. The white point was also now improved to 6523k which corrected the slightly too cool (6% deviance) default setup. The brightness control adjustment had reduced the luminance to a comfortable level now and contrast ratio remained good and basically on spec at 959:1. Colour accuracy of the resulting profile was very good, with dE average of 0.3 and maximum of 1.1. LaCie would consider colour fidelity to be very good overall. Gradients remained mostly smooth with only a little banding introduced in darker tones. To be honest there weren’t many improvements over just our optimal OSD adjustments in the section above, and while that setup had a slightly different gamma curve, it avoided any banding at all.

You can use our settings and try our calibrated ICC profile if you wish, which are available in our ICC profile database. Keep in mind that results will vary from one screen to another and from one computer / graphics card to another.

Hardware Calibration

The 27GN950 supports hardware calibration where you can programme the hardware LUT (Look Up Table) and negate the need for ICC profiles and colour management within your applications. This can save the calibration to the screen itself which means the settings are saved for all your applications and uses, and should in theory also give you a more accurate result, with better control of the hardware itself. This can also help retain contrast, tonal values and ensure gradients remain smooth as corrections are carried out at the hardware level, and not at the graphics card level.

For this you will need to install LG’s free provided ‘Calibration Studio’ software (v 5.1.4 at the time of writing).

The software provides a simple and easy-to-use configuration page as shown above where you can choose your colour space (gamut), brightness, colour temperature and gamma targets. The whole process is automated and screen adjustments and settings are automatically updated for you, with the screen entering the ‘Calibration 1’ preset mode as well. It does take quite a long time to complete a calibration, around 16 min 30 seconds.

At the end of the process you are presented a simple results page as shown above confirming how closely the targets have been met. Most of the OSD controls are locked at the end, although brightness is left available which is good news if you want to change that for different times of the day, or to your liking. It won’t impact any other aspect of the calibration.

We also went through the additional ‘validation’ set on the right, this took around 3 minutes to complete.

The validation results provide a bit more detail on the calibration, including a dE result. We separately measured the colour space using ChromaPure and thankfully confirmed that the sRGB gamut had been properly emulated, measuring 97.6% sRGB, and restricting the default 132.3% sRGB coverage nicely.

We also performed a validation using the LaCie Blue Eye Pro software:

The hardware calibration had worked well, and was simple and easy to use. As we’ve said above, the sRGB colour space was now being nicely emulated which was great news, and this could be useful for those who want to work with standard gamut content and avoid any complications with the wide gamut display. You can always set one mode up with sRGB and another with the full Native gamut if you want, or change back to the other preset modes where wide gamut is used for gaming etc. The above report confirms the gamma, white point and luminance targets had been nicely met or were very close. There was also a nice low dE. As adjustments were being made at the hardware level tonal values were maintained and there was no banding on colour gradients at all. Contrast ratio had taken a small hit, and was now measured a 923:1, down from around 994:1 we’d seen out of the box but not by a massive amount.

We should note here that when we first tested this feature we saw an issue, flagged to us by some readers, where the hardware calibration would not be properly saved to the screen after a reboot of display power off. We spoke to LG about this who confirmed that they were issuing a new firmware for the screen to fix this problem. We had chance to test that firmware early and it did indeed fix the issue. Hardware calibrations are now properly stored and remembered.

Setup Comparisons

The comparisons made in this section try to give you a better view of how each screen performs, particularly out of the box which is what is going to matter to most consumers. We have divided the table up by panel technology as well to make it easier to compare similar models. When comparing the default factory settings for each monitor it is important to take into account several measurement areas – gamma, white point and colour accuracy. There’s no point having a low dE colour accuracy figure if the gamma curve is way off for instance. A good factory calibration requires all 3 to be well set up. We have deliberately not included luminance in this comparison since this is normally far too high by default on every screen. However, that is very easily controlled through the brightness setting (on most screens) and should not impact the other areas being measured anyway. It is easy enough to obtain a suitable luminance for your working conditions and individual preferences, but a reliable factory setup in gamma, white point and colour accuracy is important and some (gamma especially) are not as easy to change accurately without a calibration tool.

From these comparisons we can also compare the calibrated colour accuracy, black depth and contrast ratio. After a calibration the gamma, white point and luminance should all be at their desired targets.

Default setup of the screen out of the box pretty decent overall despite the fairly relaxed factory calibration criteria. A good gamma and white point setup along with a wide DCI-P3 colour gamut and good contrast ratio (for an IPS panel). The sRGB mode worked well at emulating the smaller colour space after the firmware fix was applied, but left a little to be desired in terms of gamma setup. The calibrated results were excellent, and hardware calibration support was very welcome for great control, flexibility and accuracy in setup, even beyond colour managed workflows and for gaming and multimedia. It was also pleasing to see a decent IPS contrast ratio of 959:1 after calibration here, as previous Nano IPS screens we’ve tested have suffered a bit there like the 27GL850 at 848:1 and 38GL950G at 828:1 for instance. Those were criticised a bit for their lower-than-typical contrast ratio, so it was good to see that the 27GN950 didn’t suffer the same fate.

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Viewing Angles

Above: Viewing angles shown from front and side, and  from above and below. Click for larger version

Viewing angles of the screen were very good as you would expect from an IPS panel. Horizontally there was very little colour tone shift until wide angles past about 45°. A slight darkening of the image occurred horizontally from wider angles as you can see above as the contrast shifted slighting. Contrast shifts were slightly more noticeable in the vertical field but overall they were very good. The screen offered the wide viewing angles of IPS technology and was free from the restrictive fields of view of TN Film panels, especially in the vertical plane. It was also free of the off-centre contrast shift you see from VA panels and a lot of the quite obvious gamma and colour tone shift you see from some of the modern VA panel type offerings.

Above: View of an all black screen from the sides. Click for larger version

On a black image there is a characteristic pale glow introduced to the image when viewed from a wide angle, commonly referred to as “IPS glow”. This type of glow is common on most modern IPS-type panels and can be distracting to some users. If you view dark content from a normal head-on viewing position, you may see this glow as your eyes look towards the edges of the screen. The level of glow on this panel was a little more purple in colour than the other Nano IPS panels we’ve tested like the LG 27GL850 and LG 38GL950G where it was a bit more white, but it still remained fairly typical for an IPS-type panel.

This type of glow is common on most modern IPS-type panels and can be distracting to some users. If you view dark content from a normal head-on viewing position, you may see this glow as your eyes look towards the edges of the screen depending on your viewing position. It will also be more noticeable in darker ambient light conditions and if you’re viewing a lot of dark content. Some people may find this problematic if they are playing a lot of darker games or watching darker movies. In normal day to day uses you couldn’t really notice this unless you were viewing darker content. If you move your viewing position back, which is probably likely for movies and games keep in mind, the effect reduces as you do not have such an extreme angle from your eye position to the screen edges.

Panel Uniformity

We wanted to test here how uniform the brightness was across the screen, as well as identify any leakage from the backlight in dark lighting conditions. Measurements of the luminance were taken at 35 points across the panel on a pure white background. The measurements for luminance were taken using BasICColor’s calibration software package, combined with an X-rite i1 Display Pro colorimeter with a central point on the screen calibrated to 120 cd/m². The below uniformity diagram shows the difference, as a percentage, between the measurement recorded at each point on the screen, as compared with the central reference point.

It is worth noting that panel uniformity can vary from one screen to another, and can depend on manufacturing lines, screen transport and other local factors. This is only a guide of the uniformity of the sample screen we have for review.

Uniformity of Luminance

Luminance uniformity of the screen was very good on our sample, with all of the screen within a 10% deviance of the centrally calibrated area which was pleasing. The bottom area was slightly brighter than the top, and it dipped a little in the upper corners but not by anything major or noticeable.

Backlight Leakage

We also tested the screen with an all black image and in a darkened room. A camera was used to capture the result. There were a couple of areas where the backlight shone through a bit more brightly in the lower corners, but they were hard to see in normal usage.

Note: if you want to test your own screen for backlight bleed and uniformity problems at any point you need to ensure you have suitable testing conditions. Set the monitor to a sensible day to day brightness level, preferably as close to 120 cd/m² as you can get it (our tests are once the screen is calibrated to this luminance). Don’t just take a photo at the default brightness which is almost always far too high and not a realistic usage condition. You need to take the photo from about 1.5 – 2m back to avoid capturing viewing angle characteristics, especially on IPS-type panels where off-angle glow can come in to play easily. Photos should be taken in a darkened room at a shutter speed which captures what you see reliably and doesn’t over-expose the image. A shutter speed of 1/8 second will probably be suitable for this.

General and Office Applications

The 27GN950 features a 3840 x 2160 Ultra HD resolution, all packed in to a 27″ sized screen. The higher resolution is not about providing more screen real-estate here and we need to move away from thinking about LCD resolution in that manner. In fact it is arguable that the wide range of 2560 x 1440 resolution panels in the 27″ sector are about as high a resolution as you want to go, without making fonts and icons too small natively. That provides a pretty comfortable option to work with day to day.

Here, with the resolution being so much higher it is about providing a sharper and crisper image, while still operating with a similar desktop area and similar font size to the 1440p models. It is providing a higher pixel density (Pixels Per Inch, PPI) to improve the degree of definition to the image. You need to us operating system scaling to handle this properly. If you try and run the screen without any scaling at 3840 x 2160 the 0.156mm pixel pitch makes everything far too small and tiny. In our view you need a screen of about 40″ in size (like the Philips BDM4065UC for example) to use an Ultra HD or 4K resolution effectively without OS scaling. On this 27″ model, if you increase the scaling to 150%, you actually end up with the same workspace area as 2560 x 1440, but at a much higher PPI pixel density – and therefore a sharper image. Have a read of Eizo’s very useful article for some more information on the whole matter. For those wanting a high pixel density for CAD, design, photo work etc, this is a really good option. The image was very sharp and crisp and text was very clear. It is a little debatable whether you will gain much benefit from the higher PPI on a screen this size compared with a 2560 x 1440 standard model, but some may notice picture quality and sharpness improvements.

Keep in mind that not all Operating Systems and applications handle scaling the same. More recent versions of Windows (8.1 and 10) tend to handle it all better, and recent versions of Mac OS are pretty solid as well. Some applications and games don’t handle scaling correctly and so you can end up with some things with very minute text and fonts and some things which don’t scale completely in every place. Keep this in mind if you’re selecting any super high resolution display as it could be an important factor. You need to ensure you have the necessary operating system and applications to handle scaling effectively for your needs. It does make life a bit more complicated than if you just ran at a native resolution, which is where the more common 2560 x 1440 res fits in to the 27″ display space.

We should note here that the 27GN950 offered some of the best resolution interpolation scaling (scaling from the screen as opposed to from the OS software) we have seen from any 4K screen. If you set your resolution to 2560 x 1440 the image still looks very sharp and clear, and doesn’t blur the text too much like most 4K screens do when scaling. In fact the image looked so good, it was not far off a native 1440p screen we felt when comparing side by side. Not quite as sharp, but close. The same can be said for running at 1080p. Obviously you get much larger fonts and a reduced desktop space at 1080p, but the text still looked clear and sharp and the scaling was handled well. This is great news on both fronts for those who might want to input a non-native resolution for PC gaming or external devices. PC gaming for instance will be much less of a system drain at 1440p than at 4K, allowing you to potentially push up to higher frame rates and use higher settings. Knowing that the sharpness and picture quality is still very good at 1440p is a big bonus. Console gaming at lower resolutions should also be decent, you don’t need to worry about having 4K support necessarily. We believe this must be related to the scaler used on this screen, as there’s no specific image sharpening modes on this model. Note that this doesn’t seem to apply when in HDR mode, that seems to interfere with the sharpness at non-native resolutions although 4K remains fine.

The light AG coating of the panel is welcome, and much better than the grainy and dirty appearance of older IPS AG coatings. The wide viewing angles provided by this panel technology on both horizontal and vertical planes, helps minimize on-screen colour shift when viewed from different angles. The default setup of the screen was reasonable as well, offering an accurate gamma curve and decent contrast ratio for an IPS panel. The white point is a bit too cool but not by much. You can correct this easily enough through the OSD menu. There is support for both the native DCI-P3 colour space (default mode) and an emulated sRGB colour space if you need it after the latest firmware is applied which fixed the sRGB emulation. Those wanting to work with wide gamut content for multimedia and HDR can achieve good coverage of the DCI-P3 colour space as well. The availability of hardware calibration was very welcome, allowing you to calibrate and control your screen with high levels of accuracy, storing the results on the screen itself to ensure this is retained for all uses, not just those ICC-profile aware applications and colour managed workflows.

The brightness range of the screen was wide with the ability to offer a luminance between 465 and 90 cd/m². This might not be quite dark enough for some people who want to use the screen in lower ambient light conditions, including darkened rooms but it’s not bad. A setting of 7 in the OSD brightness control should return you a luminance close to 120 cd/m² out of the box. The brightness regulation is controlled without the need for the use of Pulse-Width Modulation (PWM), and so those who suffer from eye fatigue or headaches associated with flickering backlights need not worry.

There are no specific blue light filter settings available in the OSD menu on this display. There is an ‘Reader’ preset mode which makes the image warmer, to about 5271k and that might be useful for a lot of text work or reading, especially at night. This reduced the blue light output as shown above as a result of the warmer colour temp.

There are 2x USB 3.0 ports provided on the back of the screen which are reasonably easy to access, but there are none available on the sides of the screen for really quick use. There are also no other extras like ambient light sensors, motion sensors or card readers on this screen which are sometimes useful for office-type uses. There is a headphone jack but that’s about it. There is also a good range of adjustments offered from the stand which provided a stable and sturdy base, with smooth and easy adjustments. We did miss side to side swivel a bit which felt like an odd omission.

Gaming

The screen uses overdrive technology to boost pixel transitions across grey to grey changes as with nearly all modern displays. The part being used is an LG.Display LM270WR8-SSA1 Nano IPS technology panel. Have a read about response time in our specs section if you need additional information about this measurement. There is control for the overdrive impulse available via the OSD menu as listed above, but there is no variable overdrive used here which is a feature of Native G-sync hardware modules (not featured on this screen).

We use an ETC M526 oscilloscope for these measurements along with a custom photosensor device. Have a read of our response time measurement article for a full explanation of the testing methodology and reported data.

We first of all carried out some response time measurements at the native maximum 144Hz refresh rate. Through some visual tests we were able to determine that there was only small differences in motion clarity as you increased from Off > Normal > Fast mode, and in the Fast mode we saw no sign of any overshoot artefacts at this refresh rate. We started there for our measurements rather than measure all the modes unnecessarily. In the Fast mode we measured a 5.0ms G2G average and no overshoot at all. Motion looked smooth and clear, aided of course by the high refresh rate of 144Hz. Further measurements and motion clarity pursuit camera photos to follow a bit later.

Above: pursuit camera test in ‘Faster’ mode at 144Hz showing high overshoot levels

Like the other LG Nano IPS displays we’ve tested like the 27GL850 and 38GL950G the 1ms G2G spec is only possible if you switch the monitor to the maximum ‘Faster’ response time setting which is documented on many of the LG.com regional pages and in the spec sheet. The overall response times have improved noticeably, down from 5.0ms G2G in the ‘Fast’ mode to a very low 3.1ms G2G average here. Some transitions do reach even lower than 1ms, the best we measured was 0.7ms so the screen is living up to the spec basically which says it can reach 1ms in the ‘Faster’ mode. However, this is at the cost of some massive levels of overshoot. In our measurements the overshoot crept up to as high as 201% which introduced some horrible overshoot artefacts in practice with lots of pale halos clearly visible especially on lighter coloured backgrounds.

We will repeat what we said in the 27GL850 and 38GL950G reviews. Obviously this 1ms G2G spec is complete marketing, and is not something achievable in practice at all without serious side-effects. There’s no denying that the panel is fast anyway, even in the more modest and sensible ‘Fast’ mode, and we don’t want to take anything away from it’s performance in what we consider the optimal ‘Fast’ mode as it’s very impressive. To be honest we’d have rather LG had stuck with a more traditional response time spec like 4 ms G2G and delivered a great performance in that range, than push unrealistic and unachievable marketing figures that don’t live up to the hype. Stick to the ‘Fast’ mode on this screen for optimal performance.

Refresh Rate

The screen supports VESA Adaptive-sync and so can support variable refresh rates from both AMD FreeSync and NVIDIA G-sync systems. The VRR range supported is between 48 and 144Hz (native maximum refresh rate). The screen has also been officially certified by NVIDIA under the ‘G-sync Compatible’ and AMD ‘FreeSync Premium Pro’ schemes which should give reassurance to the level of performance in VRR. The support for G-sync and FreeSync will be very useful given the significant system demands of running a screen at 4K resolution and at high refresh rate. It was of course very good to see it included here. You might also want to read our detailed article about Variable Refresh Rates here for more information.

We will also touch on HDMI VRR support and next generation consoles like the PS5 and Xbox Series X. The screen has only an HDMI 2.0 input and so cannot support HDMI-org VRR, but it can support FreeSync over HDMI at least. This allows refresh rates up to 60Hz at 4K, and up to 120Hz at 1080p and 1440p resolutions. You will need to check if your games console can support FreeSync over HDMI if you want to be able to use VRR on this monitor. See our How to Buy a Monitor for Playstation 5 or Xbox Series S/X article for more information about this.

One other consideration for console gaming might be the native screen timings when using HDMI. In the “TV” section of the graphics card settings (labelled “Ultra HD, HD and SD”) we saw options only for 4K and 1080p. There was not a native 1440p mode in this section and so you may find consoles struggle if trying to output 1440p for whatever reason, if the screen is reporting back to the device that it’s not a natively supported mode. 1440p is available within the “PC” section though of course. Probably not an issue here though as the screen can accept a 4K input anyway and natively display it.

Display Stream Compression (DSC)

Unlike first generation 4K @ 144Hz screens, the LG 27GN950 utilises VESA’s ‘Display Stream Compression’ (DSC) technology. Early 4K @ 144Hz displays without DSC relied on two different methods to support the full resolution and refresh rate. Models like the Asus ROG Swift PG27UQ (one of the first to market) required a drop in colour capability to power the higher resolutions. Up to 98Hz you could run at full 10-bit colour depth and 4K resolution. Above that and up to 120Hz you had to drop to 8-bit colour depth, which to many looks no different in practice anyway – especially when you consider not every game even supports 10-bit in the first place. So in reality those early screens were perfectly fine up to 120Hz in most cases. To reach the full 144Hz refresh rate (or even consider anything higher) you did however have to use a colour compression option called ‘chroma sub-sampling’ which does negatively impact the image quality. It’s not really very noticeable in games and multimedia, but certainly more noticeable in desktop use where fonts can look blurred and show colour fringing. This was seen as a  negative for those early 4K @ 144Hz displays and put some people off. You can read our review of the PG27UQ which talks a lot more about chroma sub-sampling and the colour sacrifices needed for the higher refresh rates on those first generation displays.

To get around this limitation and allow 4K @ 144Hz to be used without colour sacrifice another option was later introduced on other displays. Models like the Acer Nitro XV273K used a dual-DisplayPort method instead, allowing you to connect two cables from your graphics card to the screen and double the bandwidth capability. This allowed 4K @ 144Hz and with 10-bit colour depth (and no chroma sub-sampling needed) but unfortunately means that you could not use variable refresh rates (G-sync/FreeSync) which was again another problem.

We later tested the Asus ROG Strix XG27UQ which was one of the first to provide another answer to the problem in the form of DSC (Display Stream Compression). This is a VESA standard that allows compression of the image in a reported “visually lossless” way. This negates the need for colour compression from reduced chroma or any other means, and has been added to the display’s DisplayPort 1.4 connection. VESA have a whitepaper on DSC if you want to know a bit more about it. Like the XG27UQ, the LG 27GN950 uses DSC to help support the high resolution and refresh rate here.

Important note: Graphics Card Support for DSC

You need to keep in mind that only modern graphics cards support DSC. You will need a GeForce RTX 20 series, AMD Radeon RX 5700 or higher graphics card for this to be featured but make sure you check the spec of the card you have to know if it will support DSC. If you have an older graphics card then you can of course still use the screen, but not to its full capability. In fact on the 27GN950 there is no option to drop the colour depth / chroma and push to the higher refresh rates it seems. Here is a summary of what is possible from a refresh rate point of view:

So from an older non-DSC card keep in mind that the maximum refresh rate you can achieve is 95Hz, even if you were willing to drop colour depth or chroma to lower levels. This also applies at non-native resolutions like 1440p and 1080p, 95Hz appears to be the maximum allowed, at least with native screen timings.
 

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We carried out our testing using a brand new NVIDIA GeForce RTX 3090 graphics card, that supports DSC. There was nothing specific to enable from the drivers or software, we were now just able to select 3840 x 2160 resolution and run at 144Hz, 10-bit colour depth and full RGB straight away. 144Hz was also now available at 1440p and 1080p resolutions. We were pleased that there was no visual loss to our eyes and in our range of tests which was excellent. You can certainly see chroma sub-sampling when you use that old method especially in desktop applications, but that was not necessary now that DSC was being used. We saw now additional lag either when using this and no noticeable side-effects. This seemed to work very nicely to allow you to squeeze more out of the bandwidth of DisplayPort 1.4. Keep in mind also that to power a screen at 4K and up to 160Hz you are going to need a very good system and high end graphics card anyway.

Response Times and Refresh Rate

There’s various things you need to consider when it comes to response times and gaming, particularly on a display with high refresh rate support. Gaming screens invariably give you a control for the overdrive impulse in the OSD menu which can help you tweak things, but response time performance and overshoot levels can vary depending on the active refresh rate. This behaviour is often different depending on whether the screen is a traditional G-sync screens (with hardware module) or whether it’s an adaptive-sync screen as well, and not all screens behave in the same way. We always try to test each variable in our reviews but the key considerations you need to make are:

1. Performance at 60Hz – this is important if you want to use an external games console (or other device like a Blu-ray player etc) which typically run at 60Hz. Response time performance may well be different than at the higher refresh rates supported, and you may need a different overdrive setting for optimal experience.
    
2. Performance during VRR (Variable Refresh Rate) – bearing in mind that the refresh rate will fluctuate anywhere from 1Hz up to the maximum supported by the screen (e.g. 1 – 144Hz on a 144Hz display). It’s important to understand if the response times and overshoot will vary as the refresh rate changes. There may be a need to switch between different overdrive settings in some cases, depending on your usually attained refresh rate output and graphics card capability. This can sometimes become fiddly if your refresh rates fluctuate a lot, especially between different games, so it’s always easier if you can leave a display on a single overdrive setting which is suited to the whole range. Some screens also feature “variable overdrive” which helps control the response times and overshoot depending on the active refresh rate. This is particularly apparent with traditional G-sync module screens.
    
3. Performance at fixed refresh rates including maximum – this is important for those who have a powerful enough system to consistently output a frame rate to meet the max refresh rate capability of the screen. They may want to run at max refresh rate without VRR active, or even is VRR is active they may know they will be consistently at the upper end of the range. Many gaming screens show their optimal response time performance at the maximum refresh rate. Knowing the performance at high fixed refresh rates may also be applicable if you want to use any added blur reduction backlight which typically operate at a fixed refresh rate.
    
4. Whether the response times can keep up with the frame rate – you will also want to consider whether the response times of the panel can consistently keep up with the frame rate. For instance a 144Hz screen sends a new frame to the display every 6.94ms, so the pixel response times need to ideally be consistently and reliably under this threshold. If they are too slow, it can lead to added blurring in practice and sometimes make the higher refresh rates unusable in real life. We consider this in our analysis.
    

We measured the response times in the optimal ‘Fast’ overdrive mode across a range of refresh rates as shown above. The response times themselves remained consistent across the range, measured at 5.0ms G2G average in each case. The thing that changed was the overshoot, which crept up as the refresh rate lowered. The screen does not include variable overdrive, which had it been available could be used to offset this overshoot increase by increasing the response times a little as refresh rate lowers. In the absence of that, you have the same overdrive timings at all refresh rates which leads to some increase of the overshoot at lower refresh rates.

The overdrive has been optimised here for achieving a good balance between driving faster response times, and avoiding too much overshoot creeping in at the lower refresh rates. We never felt that the overshoot became too noticeable or distracting in practice, and it’s only really at the very low end where you might start to see a few pale halos appear, but they are very slight. You aren’t going to see any issue with the overshoot in practice we don’t think.

If you were worried about possible overshoot at 60Hz for console gaming (assuming no support for 120Hz) or external devices you can also drop down to the ‘Normal’ response time setting which completely eliminated the overshoot, but response times were not quite as fast as a result. In practice there was not much to separate the two modes, but it’s there if you want it.

Overclocking

The refresh rate of the 27GN950 was always listed as 160Hz in the original press material dating all the way back to Dec 2019 and as we reported on in our original news piece back then. This was conspicuous by its absence though in the final spec and product pages from LG and was nowhere to be seen when we first received the display either. 144Hz was the maximum available and there was no sign of any overclocking feature in the OSD menu either to push it higher. Had it been dropped by LG?

In speaking to LG about some of the bugs we’d experienced with the sRGB mode and hardware calibration (now fixed ad discussed earlier), they also gave us early access to a new feature that was being added with the same new firmware to enable the missing 160Hz overclocking mode! The new firmware adds this feature in to the OSD menu and we are told that this delay to the feature was because of an issue with DSC (Display Stream Compression) with NVIDIA and that it has been addressed with their latest drivers, v457.30 from 9th Nov 2020. You will need to make sure you have the latest version of the drivers from NVIDIA to ensure this feature works properly. With the new firmware installed we had access to the overclock setting in the menu as shown above.

Thanks to DSC we can run the screen at 4K @ 160Hz while also keeping 10-bit colour depth and full range RGB. Note that the overclocked refresh rate of 160Hz is only available at 4K resolution, it is not available at 1080p or 1440p.

We measured the response times in this mode as well which showed the same overall performance as the other refresh rates, and an average 5.0ms G2G response time. At this high refresh rate, and like 144Hz mode, there was no overshoot at all.
 

Gaming Summary

Recommended Settings

Optimal Refresh Rate	160Hz (Overclocked, at 4K only)
Optimal Overdrive Setting (for above)	Fast
Optimal Overdrive Setting for 60Hz	Fast / Normal
Optimal Overdrive Setting for VRR	Fast

     Detailed Measurements at 160Hz

We carried out some further response time measurements at 160Hz which is the maximum refresh rate of the screen with the overclock feature enabled. This slightly extended refresh rate gives you a little boost over 144Hz and seemed to work well, so why not use it if you can? Response time performance should be pretty consistent across the refresh rate range anyway, so the above also applies really at 144Hz, or near enough.

We measured an average 5.0ms G2G response time here which was in line with the figure we had from our smaller sample set earlier. There was basically no overshoot at all, save for one transition where there was a very small 6.2% undershoot measured. The higher refresh rates supported by the screen helped improve motion clarity and reduce perceived  blur, making the screen far better for gaming than 60Hz-only models. You get higher frame rate support as well. If you want to game at a lower resolution like 1440p or 1080p then you will have a maximum of 144Hz available (from a DSC card) but the response time performance is basically the same as above.

Above: pursuit camera photos in ‘Fast’ mode at 160Hz showing very good motion clarity

This was a very good performance from the 27GN950 with very fast response times and very good motion clarity. You get excellent picture quality and sharpness from the 4K resolution, combined here with high refresh rates and without the need to sacrifice colour performance.

Refresh Rate Compliance

In this section for our reviews we look at the response time behaviour across the range of supported refresh rates and consider whether they are sufficient to keep up with the frame rate demands of the screen. The grey line on the graph shows the refresh rate threshold, that being the average G2G response time that the panel needs to be able to achieve to keep up properly with the refresh rate and frame rate. For instance at a 60Hz refresh rate the response times need to be consistently and reliably under 16.67ms, while at 144Hz refresh rate the response times ideally need to be under 6.94ms to keep up with the frame rate demands. If they are not then this can lead to some additional smearing and blurring on moving content as the pixels can’t keep up. For these tests we will plot the average G2G figure at a range of measured refresh rates, while operating at the optimal overdrive control.

The table to the right then explains whether that overdrive control needs to be adjusted by the user depending on the refresh rate (not ideal), or whether adaptive overdrive is utilised to keep things simple. Ideally you’d want to be able to stick with a single mode for all refresh rates especially when you consider how these will vary during VRR. We also include a measurement of the % of the overall response time measurements that were within the refresh rate, as well as a slightly more lenient measurement of how many were within the refresh rate window within a 1ms leeway.

The response time behaviour of the 27GN950 is consistent across the whole refresh rate range, with an average 5.0ms G2G measured from 60Hz all the way up to 160Hz. There is very good compliance to the refresh rate as a result, meaning no additional smearing or blurring is introduced. At maximum 160Hz refresh rate 96.7% of the measured transitions were within the refresh rate window which was excellent.

Gaming Comparisons

We have provided a comparison of the display against many other gaming screens we have reviewed in a similar size range and across a range of panel technologies. This table is now split by panel technology to make life a bit easier and for quicker comparison.

Perhaps unsurprisingly the performance of the 27GN950 was very similar to the LG 27GL850 in terms of response times, refresh rate support and motion clarity. The 27GN950 obviously offers 4K resolution and some other features, whereas the 27GL850 was “only” 1440p, but the Nano IPS panels performed very similarly when it came to these other areas. A very solid performance here. It did perform better than the Asus ROG Strix XG270UQ (which also offered 4K resolution, 144Hz refresh rate and uses DSC to avoid colour sacrifice). That model had an average 6.8ms G2G response time and couldn’t keep up as well with the refresh rate demands.

Additional Gaming Features

• Blur reduction mode – there is no blur reduction mode offered on this screen despite the high refresh rate. This is likely due to the KSF LED backlight which provides the wide gamut here, but has a slow red colour decay for strobing backlights unfortunately. Blur reduction was left off the other LG Nano IPS displays we’ve tested like the 27GL850 or 38GL950G as well, presumably for the same reason. ViewSonic had added it to their XG270QG display which used the same Nano IPS panel as the 27GL850 and we had seen some issues with the blur reduction because of the backlight in that review.
   
• Aspect Ratio Control – the screen offers three modes for aspect ratio control. These are ‘full wide’ (which will stretch whatever the input aspect ratio is to fill the screen), ‘original’ (which will maintain the source aspect but fill as much of the screen as possible) and ‘just scan’. The ‘original’ mode will be useful for supporting non-native aspect ratios, although the 16:9 format here is very common so you might not need it much. There’s no 1:1 pixel mapping mode for those who like to use that, although since the screen scalers handles non-4K resolutions very well, that might not be an issue either.

• Preset Modes – There are quite a few gamer-oriented modes available in the ‘picture mode’ preset mode menu including FPS and RTS modes. There are also two customisable user modes called Gamer1 and Gamer2. So it should be easy to set the screen up to your liking for different uses if you want.
   
• Additional features– there are a couple of added features in the OSD which are a ‘black stabilizer’ control, to help boost gamma in darker content and bring out details. There is also a ‘cross hair’ graphic option.

Lag

Read our detailed article about input lag and the various measurement techniques which are used to evaluate this aspect of a display. The screens tested are split into two measurements which are based on our overall display lag tests and half the average G2G response time, as measured by our oscilloscope. The response time element, part of the lag you can see, is split from the overall display lag and shown on the graph as the green bar. From there, the signal processing (red bar) can be provided as a good estimation of the lag you would feel from the display. We also classify each display as follows:

Lag Classification

• Class 1) Less than 8.33ms – the equivalent to 1 frame lag of a display at 120Hz refresh rate – should be fine for gamers, even at high levels
• Class 2) A lag of 8.33 – 16.66ms – the equivalent of one to two frames at a 120Hz refresh rate – moderate lag but should be fine for many gamers. Caution advised for serious gaming
• Class 3) A lag of more than 16.66ms – the equivalent of more than 2 frames at a refresh rate of 120Hz – Some noticeable lag in daily usage, not suitable for high end gaming

The total lag measured was a very impressive 2.75ms total. The pixel response times account for around 2.5ms, and so we can say that there appears to be around 0.25ms of signal processing lag on this screen which is super low. A solid result from this display and making it suitable for fast and competitive gaming.

Movies and Video

The following summarises the screens performance for videos and movie viewing:

Category	Display Specs / Measurements	Comments
Size	27″ widescreen	Fairly typical for a desktop monitor nowadays and smaller than TV’s by a lot
Aspect Ratio	16:9	Well suited to most common 16:9 aspect content and input devices
Resolution	3840 x 2160	Can support native Ultra HD (4K) and 1080p content
HDCP	Yes v2.2	Suitable for encrypted content including the latest v2.2
Connectivity	1x DisplayPort 1.4 and 2x HDMI 2.0	Useful additional 2x HDMI input for external Blu-ray players or games consoles. Does not feature the latest HDMI 2.1 though for next gen games consoles (no desktop monitor does yet)
Cables	DisplayPort and HDMI	Useful to have both included in the box
Ergonomics	Tilt, height, rotate	Very easy to use adjustments with smooth and stable stand. Missing side to side swivel that can be useful for movie viewing from a different position though
Coating	Light Anti-glare	Provides clear image with no graininess, but avoids unwanted reflections of full glossy solutions
Brightness range	90 – 465 cd/m2	Good adjustment range offered including a high max brightness and reasonable darkened room adjustment range. Could have maybe done with a bit better control at the bottom end for really dark viewing conditions. Backlight dimming is free from PWM and flicker free.
Contrast	959:1 after calibration	Decent enough contrast ratio for an IPS technology panel close to spec and better than other Nano IPS panels we’ve tested before, although still not as high as you can get from VA panels of course
Preset modes	None	There are no specific preset modes for movie viewing in the menu but you can easily set up one of the other modes to your liking
Response times	5.0ms G2G with low/moderate overshoot fast mode (60Hz)5.9ms G2G with no overshoot in normal mode (60Hz)	Response times are very good on this panel. For 60Hz content and external devices the ‘Fast’ mode showed low levels of lag, nothing really obvious in practice. Dropping to the ‘normal’ mode is also viable and removes all the overshoot problems, without major impact to response times
Viewing angles	Very good	Thanks to the IPS panel technology, suitable for viewing from a wide range of positions. Pale IPS glow on dark content could present a problem from some wider angles especially in darker room conditions
Backlight bleed	No bleed	No noticeable bleed or leakage on our sample. Will vary from sample to sample
Audio	Headphone output	No integrated speakers on this model but a headphone jack is provided
Aspect Ratio Controls	Full screen, original and just scan options	The default 16:9 aspect ratio is likely to serve most needs here anyway but the provided ‘original’ mode should then cover anything else nicely
PiP / PbP	Neither supported	n/a
HDR support	See below	see following section

HDR (High Dynamic Range)

The screen can accept an HDR10 input signal and supports the moderate HDR 600 standard. Thankfully unlike the pretty pointless HDR400 level, this does necessitate some form of local dimming, so it is at least capable of improving the dynamic range (contrast) when used in some ways. The number of dimming zones is limited though so don’t expect miracles. Once HDR is enabled from Windows the screen pops up a little “HDR” logo to confirm you’ve entered HDR mode. In the OSD menu you still have access to a few of the preset modes but not all of them. The default ‘Gamer1’ mode has a “Certified by VESA DisplayHDR” logo next to it now.

We had read various reports from users that with HDR enabled the image looked really washed out. We didn’t experience this, and the image remained pretty good overall with a simple “HDR on” mode from Windows. We only tested this after updating to the latest firmware so we’re not sure if that has also fixed the default HDR appearance? The brightness control went up to 100% and the screen looks brighter, although measuring the SDR brightness confirmed only 215 cd/m² so it wasn’t too bright even then. We measured the setup and confirmed gamma was pretty good at 2.1 average (4% deviance from our 2,2 target) and white point was only a little too cool at 6922k (6% out).

We did notice that running any non-native resolution looked more blurry than in SDR mode, and we lost the really good sharpness we had commented on in the office section of this review. At 1440p the text looked more fuzzy in HDR mode with no obvious way to correct it. Running at 4K was fine though of course, but perhaps the scaler doesn’t handle non-native resolutions quite as well in HDR mode as it does in normal SDR mode.

The 27GN950 is one of those screens that looks fine with HDR enabled in Windows actually, at least in our testing, with other screens often looking terrible. You probably only want to enable it for HDR content though as the 100 brightness level is too bright for normal use, and turning it down to make it more comfortable for day to day use then spoils some of the point of having HDR enabled in the first place (the higher peak brightness).

Anyway, we then tested the HDR function and local dimming. There is a setting for ‘local dimming’ in the OSD which you can turn on, off or set to auto. There are a limited number of local dimming zones on this screen so the HDR effect is pretty limited. They are arranged in, we believe, 16 vertical zones although it wasn’t very easy to count them or be sure. It’s a limited number anyway. This means you can often see each zone light up or dim as content on the screen changes, and certainly during local dimming tests like this one. It creates large vertical bands of brighter regions and doesn’t really produce a very pleasing HDR effect to be honest. We measured a peak brightness up to 747 cd/m² which was decent and a considerable beyond the expected 600 cd/m² spec in fact, and a good way beyond the max 465 cd/m² in SDR mode. The screen can reach high peak brightness for HDR content at least, even if the local dimming doesn’t offer massive improvements to overall contrast or appearance.

Because the dimming zones are large and limited in number the “local HDR contrast ratio” (i.e. measuring a black area next to the white test area) was not really much better than the native screen contrast ratio at 1358:1. If you measured a black area further away from the white test area, where the dimming zones could dim it more, then the contrast ratio was much greater reaching up to around 8500:1 maximum but still not exactly brilliant. The local dimming isn’t sufficient enough to make a big difference in local HDR contrast, but it helps a bit across the screen as a whole. The screen does however feature the necessary colour enhancements for HDR content including a wide 97.5% DCI-P3 colour gamut, and support for 10-bit colour depth content.

Conclusion

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We’ve tested a fair few 4K high refresh rate screens now, and on balance we felt the 27GN950 is the best we have reviewed so far. The ability to support the high refresh rates without needing to sacrifice colour depth or chroma was probably the key benefit over older generation screens, and the use of DSC makes this all possible. You even get a bit of a bump in refresh rate up to 160Hz for that extra bit of frame rate support and motion clarity benefits, it was nice to see this added via a new firmware by LG too. Being a new IPS panel from LG.Display we were also pleased to see that the response time performance was excellent, offering solid performance across the VRR range, very good refresh rate compliance and low levels of overshoot. Input lag was also non-existent and so overall gaming performance was really good. We would rather LG ditched the over-the-top ‘faster’ mode though and the 1ms G2G marketing claims which are just unrealistic unless you want horrible overshoot. Wait until those specs are realistic and achievable before pushing them.

It’s going to take a very powerful system to drive 4K at high refresh rates, and you will need a modern graphics card for DSC as well but it’s definitely a great looking screen if you can do that. The 4K resolution provides sharp and crisp images and an excellent level of detail. Sure, it would be nice if the screen was a bit bigger like 32″ perhaps to make better use of 4K, as on 27″ it still feels a bit small to offer major benefits, but many people will like that added level of detail for not just gaming but general usage too. While we’re on gaming, it was a bit of a shame not to see a blur reduction mode provided, although we’d rather see it left off than included if it’s not going to perform well anyway, which is likely the reason given the slow red decay on these kind of backlights.

The default setup of the screen was good and we were glad to see the sRGB emulation mode fixed via the new firmware. We felt the factory calibration criteria could have been a bit stricter, and the provided calibration report a bit more detailed though. The sRGB emulation mode was fixed but we still saw some issues with the rest of the setup in that mode, which hopefully LG can address with a future firmware. The support for hardware calibration was another big feature, and something that separates the 27GN950 from most gaming screens and certainly helps set it apart from earlier 4K @144Hz models. The hardware calibration was simple and easy to use, albeit perhaps a little time consuming. It produced great results though and could be really useful for maintaining accurate setups across all uses and applications.

We did feel the brightness adjustment was a little limited at the lower end, and we’d rather see a slightly more modest peak brightness and the ability to drop a bit lower to be honest via the brightness control. The HDR functionality was one area that was inferior on this model as compared to some early 4K @144Hz screens like the Asus ROG Swift PG27UQ and Acer Predator X27 for instance. Those models featured top end Full Array Local Dimming (FALD) backlights which offered significantly better dimming performance, far more dimming zones (384) and also supported higher peak brightness for HDR 1000. On the 27GN950 the local dimming was not very good, but better than having nothing like you would on the wide range of HDR400 screens at least. The HDR picture quality seemed good though, there was the required wide gamut and 10-bit colour support (again, not necessarily provided on an HDR400 screen) and a very good peak brightness beyond the HDR 600 spec even.

The stand was strong and sturdy and provided a good range of adjustments, although we did miss swivel a bit and it seemed odd that it was not available. The scaler seemed to be very good on this screen as well, handling non-native resolutions very well (in SDR mode) which is great news if you want to game or use external devices at non-4K resolutions.

The 27GN950 is available from Amazon in various regions, andalso if you’re in the UK from Overclockers UK. Additional links to check pricing and buy below. If you’re after a 4K, high refresh rate monitor then this is an excellent option.

Pros	Cons
4K resolution with high refresh rate up to 160Hz without colour sacrifices, thanks to DSC	HDR capability is still limited due to low number of dimming zones
Very good response times and very low lag	Stand missing swivel adjustment
Hardware calibration is a nice additional feature	Factory calibration and sRGB mode could have been tighter

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