Introduction

The monitor gaming market continues to grow at a rapid pace, with new screens offering higher and higher refresh rates. We have with us at the moment the LG 27GK750F which is LG's latest 27" gaming display, featuring a 1080p resolution TN Film panel and a native 240Hz refresh rate. It's firmly aimed at gamers and offers support also for AMD FreeSync, a 2ms G2G response time, a Motion Blur Reduction strobing backlight and a range of gaming options to play with. It might not offer the resolution of competing 1440p or Ultra HD resolution models, but it's currently the maximum available if you want to take advantage of the very high native 240Hz refresh rate. We've already tested a couple of 24.5" sized screens in the past with 240Hz refresh rate, and there's fewer 27" models available but the choice is starting to grow if you want a super-fast gaming display.

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Specifications and Features

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

The 27GK750F offers typical connectivity for a modern screen with 1x DisplayPort 1.2 and 2x HDMI 2.0 offered for video connections, and an additional 2 port USB 3.0 hub, with the ports located on the back of the screen and both supporting fast charging. The screen has an external power supply and comes packaged with the power cable and brick you need. A headphone output is also provided.

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

Power Consumption

In terms of power consumption the manufacturer lists normal usage of 30W, and <0.5W in standby. We carried out our normal tests to establish its power consumption ourselves.

Out of the box the screen used 30.0W at the default 100% brightness setting and spot on in fact to the manufacturer spec. Once calibrated the screen reached 15.8W consumption, and in standby it used only 0.6W. We have plotted these results below compared with other screens we have tested. The consumption (comparing the calibrated states) is a little lower than other 27" sized screens here, probably because we had to reduce the backlight brightness all the way down to 0% to achieve a comfortable (although still not quite low enough) luminance. It actually ended up being pretty comparable to the slightly smaller 24.5" sized 240Hz gaming screens like the AOC AGON AG251FZ and Asus ROG Swift PG258Q shown here.

Panel and Backlighting

Panel Part and Colour Depth

The LG 27GK750F features an AU Optronics M270HTN02.3 TN Film technology panel which is capable of producing 16.7 million colours. This is achieved through an 8-bit colour depth according to the LG spec. The panel part is confirmed when dismantling the screen as shown below:

Screen Coating

The screen coating is a medium anti-glare (AG) offering. It isn't a semi-glossy coating like some alternative VA-type panels, and isn't as light as some modern IPS-type panels either. It's in keeping with other TN Film panels we've tested and just a little more grainy than those VA and IPS offerings. It retains its anti-glare properties to avoid too many unwanted reflections of a full glossy coating, but does not produce an too grainy or dirty an image that some thicker AG coatings can. There were no cross-hatching patterns visible on the coating at all.

Backlight Type and Colour Gamut

The screen uses a standard gamut W-LED backlight unit as most screens today do. This offers a normal sRGB colour space, equating to around 72% NTSC coverage. There is no support for any wider colour spaces such as Adobe RGB or DCI-P3 on this model. If you want to read more about colour spaces and gamut then please have a read of our detailed article.

Backlight Dimming and Flicker

We tested the screen to establish the methods used to control backlight dimming. Our in depth article talks in more details about a previously very common method used for this which is called Pulse Width Modulation (PWM). This in itself gives cause for concern to some users who have experienced eye strain, headaches and other symptoms as a result of the flickering backlight caused by this technology. We use a photosensor + oscilloscope system to measure backlight dimming control with a high level of accuracy and ease. These tests allow us to establish

1) Whether PWM is being used to control the backlight
2) The frequency and other characteristics at which this operates, if it is used
3) Whether a flicker may be introduced or potentially noticeable at certain settings

If PWM is used for backlight dimming, the higher the frequency, the less likely you are to see artefacts and flicker. The duty cycle (the time for which the backlight is on) is also important and the shorter the duty cycle, the more potential there is that you may see flicker. The other factor which can influence flicker is the amplitude of the PWM, measuring the difference in brightness output between the 'on' and 'off' states. Please remember that not every user would notice a flicker from a backlight using PWM, but it is something to be wary of. It is also a hard thing to quantify as it is very subjective when talking about whether a user may or may not experience the side effects.

100%                                                     50%                                                     0%

Above scale = 1 horizontal grid = 5ms

Brightness and Contrast

At the top end the maximum luminance reached a high 452 cd/m² which was a fair bit higher even than the specified maximum brightness of 400 cd/m² from the manufacturer. This gives a nice bright option at the upper end if you need it, and this could be especially useful when it comes to using the blur reduction mode which we will test later on, as that makes the screen darker due to the strobing of the backlight. There was a wide 308 cd/m² adjustment range in total, and at the minimum setting you could reach down to a luminance of 143 cd/m². This was a bit of an issue, as this still leaves you with a pretty bright display even at the minimum brightness adjustment. We couldn't even reach as low as our target 120 cd/m² as a result, let alone any lower setting for more comfortable use in darkened room conditions. This was certainly a limitation of the display which should be considered. It should be noted that the brightness regulation is controlled without the need for Pulse Width Modulation for all brightness settings, so the screen is flicker free.

    

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. This is a linear relationship as you can see.

The average contrast ratio of the screen was pretty good out of the box for a TN Film panel, measured at 895:1 before calibration. This was very stable across the brightness adjustment range as you can see above.

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 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 - validates 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

• 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 - we aim for as high as possible. Any dynamic contrast ratio controls are turned off here if present

• dE average / maximum - 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

Default settings of the screen were as follows:

Initially out of the box the screen was set in the 'gamer 1' mode with a setting of 'mode 2' for the gamma, and 'custom' for the color temp modes. We will test the impact of those settings in a moment for completeness. The display was also set with a very high 100% brightness which was far too bright and uncomfortable to use. You will definitely need to turn that down although we already know from our brightness and contrast section that this screen has trouble reaching low luminance levels which might be problematic for more general, non-gaming uses. The colours felt decent and well balanced, and you could tell the screen was using a standard sRGB gamut backlight.

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) matches the sRGB colour space reference (orange triangle) closely. We measured using ChromaPure software a 100.7% sRGB gamut coverage which corresponds to 74.3% of the DCI-P3 reference and 53.3% of the Rec.2020 reference. This screen is only designed to be a standard sRGB display, so this was expected.

Default gamma was recorded at 2.3 average, with a small 5% deviance from the target. It was closer to the 2.2 target in the darker shades (2.21), but started to deviate to a higher gamma (2.43) for lighter grey shades. White point was measured at a nicely accurate 6437k, being only 1% out from our target of 6500k. There are a range of other colour temp presets available in the menu along with this 'custom' mode where you have access to the individual RGB channels for the calibration process.

Luminance was recorded at an extremely bright 477 cd/m² which is far too high for prolonged general use, you will need to turn that down. The screen was set at a default 100% brightness in the OSD menu but that is easy to change of course to reach a more comfortable setting without impacting any other aspect of the setup. You may need to turn it all the way down to 0% though to reach a more comfortable setting for every day use. The black depth was 0.53 cd/m² at this default brightness setting, giving us a moderate 905:1 contrast ratio. Colour accuracy was good out of the box with an average dE of 2.0 and a maximum of only 4.7. Testing the screen with colour gradients showed mostly smooth gradients with some gradation evident in the darker tones and also some low levels of banding in those darker shades.

We also tested the few gamma and colour temperature modes at default screen settings:

The gamma mode 3 seemed to be a little closer to our target of 2.2 with only a 3% deviance on average, although the problem with this mode was that it showed more deviance in the darker shades and this created some issues with darker tones disappearing in to black when carrying out visual tests with gradients. The mode 2 default was slightly further away from the target on average, but had a more accurate gamma curve in the darker tones so seemed to be preferable in practice. We would recommend sticking to mode 2.

The default 'custom' colour temp mode was closest to our 6500k target out of the box, and this mode also gives more flexibility as you can then change the individual RGB channels yourself, and achieve a custom white point. This was the same as the warm setting incidentally, with the medium and cool settings giving a progressively cooler appearance.

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 colorimeter was used to validate the black depth and contrast ratios due to lower end limitations of the i1 Pro device.

Calibration was a bit fiddly on this display, and it was very hard to obtain a satisfactory result. We stuck to the gamma mode 2 in the end after several calibration attempts in mode 2 and 3. Although mode 3 showed the smaller deviance overall, the gamma curve in dark tones was further adrift and this created problems with banding in darker tones. We had better results in mode 2, where the darker tones were closer to the desired 2.2. The end result of the calibration was less noticeable banding, and certainly smoother gradients in those darker tones.

The calibration software guided us through adjustments to the RGB values to reach the desired white point balance and contrast. We had to lower brightness to 0% since this was the lowest we could do on the screen, and in fact this still wasn't low enough to meet the target we were after. 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.

Average gamma was measured at 2.2 average (0% deviance) which fixed the 5% deviance we'd seen out of the box at default settings. The minor 1% white point deviance had now been corrected bringing the measured white point to 6512k. Luminance had been improved thanks to the adjustment to the brightness control and was now being measured at a far more comfortable 141 cd/m². This was still a bit bright, and it's a shame you can't get any lower than this via the OSD brightness control. You could lower the brightness of the screen further via the graphics card settings, but at the cost of reducing the contrast ratio further which is not desirable. Even without adjusting the graphics card, and sticking with this slightly high 141 cd/m², this left us a black depth of 0.23 cd/m² and a calibrated static contrast ratio of only 602:1. This was poor, even for a TN Film panel and we were not able to really improve on this through repeated calibration attempts, with different settings and modes tried. You may be better off sticking with the default out of the box settings where contrast ratio was a more respectable 905:1 and avoid the OSD and ICC profile adjustments made here. You'd have to live without the small gamma correction and dE improvements, but you would at least have a better contrast ratio and the rest of the setup was still decent enough. For gaming you're probably going to want to use brighter, more vivid and less "accurate" settings anyway.

Colour accuracy of the resulting calibrated profile was very good, with dE average of 0.7 and maximum of 1.3. LaCie would consider colour fidelity to be excellent. Testing the screen with various colour gradients showed mostly smooth transitions with only some minor gradation and slight banding in darker tones. 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.

Calibration Performance 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 was pretty good really considering it's a gaming screen and those are often set up with massively skewed gamma and colour accuracy. Just look at some of the other TN Film models in the table above for instance where gamma is often a long way off 2.2. We had a small gamma deviance of 5% here on the 27GK750F, an accurate white point and a low 2.0 dE out of the box which was pleasing. This was also combined with a 905:1 contrast ratio which is good for a TN Film panel, although of course much lower than some other competing panel technologies. So for most users this default setup should be fine.

Please see note about contrast ratio below

We came across some problems when trying to profile and calibrate the screen. The corrections to the gamma curve and profiling process seemed to have a significant negative impact on the contrast ratio, and we didn't seem to be able to achieve much more than about 602:1 despite many attempts in different modes and settings. We have included it here for completeness, but we would actually recommend sticking to the screens decent default setup instead, and therefore having a higher contrast ratio of around 905:1.

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Viewing Angles

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

Viewing angles of the screen were as you might expect from a TN Film panel. Unfortunately this panel technology is inherently poor in this field, and so viewing angles are more restrictive than other competing technologies like IPS and VA variants. Although the manufacturer will quote a viewing angle of 170 / 160 (a classic indication that a TN Film panel is being used by the way if in doubt), in practice there are some obvious contrast and colour tone shifts horizontally, and especially vertically.

As you move your head from side to side in a horizontal plane, there is a contrast shift and the image becomes more pale and introduces a yellow hue. As you move to a wider angle the image can become more washed out as well and a more yellow hue is introduced. Vertically the fields of view are more restrictive still with more noticeable contrast shifts. From above the image becomes pale and washed out, while from below there is a characteristic TN Film darkening of the image. Unfortunately vertically the viewing angles will introduce noticeable shifts in the contrast and colour tone of the image which mean that for any colour critical work it is not really very well suited. TN Film panels have long suffered from these restrictive viewing angles due to the nature of their pixel structure. They are still fine for a single user for general use and certainly the TN Film panels offer their advantages when it comes to pixel response times and refresh rate for gaming. If however, you were hoping to do any colour critical or photography work you may find these shifts in the appearance of the image difficult.

An IPS-type panel would probably be a wiser choice if you were looking for a screen with much wider viewing angles but having said that you are probably mainly interested in gaming if you are considering this screen. Remember, this screen is specifically designed for gaming, and so you will have to live with some of the sacrifices of TN Film to get the kind of gaming performance and features offered here. There are some high refresh rate gaming IPS panels available now in larger sizes as well which can offer better viewing angles than TN Film models, although they are normally priced higher and have some other characteristic differences, and so TN Film models like this still have their place for many users.

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

On a black image there is a slight pale grey tint introduced to the image when viewed from a wide angle. This isn't too severe and shouldn't present any real problems in practice. Certainly not the obvious white glow you get from most modern IPS-type panels in similar situations and fairly standard for a TN Film panel. Very similar to what we have seen from other recent gaming TN Film screens like the AOC AGON AG251FZ, Asus MG248Q, Asus ROG Swift PG278Q and BenQ XL2730Z. The glow you see from most modern IPS panels can put off some users. So on the one hand, those IPS models have much better general viewing angles than the TN Film models, but they do show more glow which some people find an issue.

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 (*in this example 138 cd/m² given the lower brightness limits of the display). 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

Uniformity of the screen was fairly good on this sample. The upper edge and top left corner in particular showed a drop in luminance by 23% in the most extreme measurements, down to 112 cd/m². As a result the upper edge was a little darker than the lower and middle regions of the panel. Around 70% of the screen was within a 10% deviance of the centrally calibrated point. It's not a screen designed for any colour critical work so these variations are not likely to cause any problems. You're more likely to experience issues with the viewing angle colour tone and gamma shifts for those kind of uses than from variances in the luminance across the panel. You shouldn't notice anything related to luminance variation for the intended uses of gaming really.

Backlight Leakage

Above: All black screen in a darkened room. Click for larger version

We also tested the screen with an all black image and in a darkened room. A camera was used to capture the result. The camera showed there was no major backlight bleed but some lighter areas of clouding along the bottom edge where the backlight is situated. This wasn't really noticeable in normal uses at all.

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

With a 1920 x 1080 resolution, the desktop real estate  of the 27GK750F feels a pretty big step down compared with all the high resolution panels we've tested, and the 27" 2560 x 1440 models we are used to using day to day. You do lose a large amount of desktop space, and although side by side split screen working is possible, it's not as easy due to the more limited resolution and space. With a 0.31125mm pixel pitch, text is comfortable and easy to read natively, providing a still fairly sharp and crisp image. It is not as sharp as the 1440p panels we've become accustomed to, or of course any ultra HD/4K resolutions where scaling is used, but it is perfectly adequate. We would have preferred a full 1440p resolution on a 27" screen like this to be honest, although it is primarily aimed at gaming. With the high 240Hz refresh rate in mind, it's probably more realistic to be powering a 1920 x 1080 resolution than 2560 x 1440 anyway for those purposes. Not to mention the fact that 240Hz panels are currently only available at 1080p maximum anyway. It's just a shame when it comes to more general office work that the resolution is pretty low.

The moderate AG coating of the TN Film panel could be considered a bit grainy, especially on white office backgrounds to a lot of people. It's not as clear as modern IPS coatings or any semi-glossy VA solution. Still, it's not as grainy as old IPS panels and is on par with other TN Film matrices we've tested. Perhaps the main issue with this panel technology though is the restrictive viewing angles, making contrast and colour tone shifts a bit of a problem when it comes to colour critical work. They are the same here as other TN Film panels, being restrictive especially vertically. The screen is fine when viewed head on though really for office and text work, but for colour critical work or photo editing etc you'd definitely be better off with an IPS-type panel. The default setup of the screen was reasonable for day to day use with a well set white point and pretty low dE. The gamma was slightly off but nothing major. Actually we found that trying to calibrate the screen to correct the gamma and improve the dE a bit more had the knock on effect of dramatically reducing the contrast ratio, so we would probably recommend avoiding that to be honest. The out of the box setup is adequate for some general day to day uses, and you're not going to be wanting to do any real colour work on this screen anyway because of the inherent drawbacks of the TN Film panel.

You will definitely want to lower the brightness from the very bright 100% setting, but one of the limitations of this model is the inability to reach low enough luminance levels. Even at 0% brightness setting, the luminance is a bit too high (143 cd/m²) for the recommended 120 cd/m² we would normally want to use for an LCD screen in normal lighting conditions. This bright screen might be better for gaming, and certainly for those using the low motion blur backlight modes, but it's a bit too bright for general day to day office use unless you're in a pretty bright room. At night, in lower ambient light, the inability to reduce this down to a lower level is a bit of an issue. On a positive note, 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 is a 'reader' preset mode which was a fair bit warmer than the default 'gamer 1' mode which is around 6500k white point. You cannot change any settings really in that 'reader' preset, other than the brightness which thankfully it does store and remember. But it might be useful to have as a quick access mode for warmer reading conditions, especially if you are using the main gamer 1 preset for, well, gaming. There was no audible noise or buzzing from the screen, even when specifically looking for it using test images with a large amount of text at once. The screen also remains cool even during prolonged use.

The screen offers 2x USB 3.0 ports (with fast charging capabilities also) which is handy, although they are on the back of the screen with the input connections so not really that easy access. There are no integrated stereo speakers on this model, but there is a headphone output. There aren't any other extras like card readers or ambient light sensors offered though which can sometimes be useful in office environments. The stand offers a wide range of adjustments which is great news, allowing you to obtain comfortable viewing positions.

 
Responsiveness and Gaming

The 27GK750F is rated by LG as having a 2ms G2G response time (in the fast mode). A 1ms response time is also quoted for the Motion Blur mode which we will talk about more in a moment. That relates to the strobing blur reduction backlight, so we will first look at the panels pixel response times. The screen uses overdrive / response time compensation (RTC) technology to boost pixel transitions across grey to grey changes as with nearly all modern displays. There is a user control in the OSD menu for the overdrive under the 'Response Time' setting with 4 options available - Off, Slow, Normal and Fast. The part being used is the AU Optronics M270HTN02.3 TN Film technology panel.  Have a read about response time in our specs section if you need additional information about this measurement.

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 carried out some initial response time measurements in each of the overdrive settings, along with some visual tests. We didn't bother testing the 'Off' mode as we knew we wouldn't want to use it. The response times remained basically consistent regardless of the refresh rate, from 60Hz all the way up to the maximum 240Hz which was good news. We don't need to worry about varying response times here as the refresh rate changes.

As you can see above, the response times were a little slow in some cases in the 'Slow' setting, particularly on some of the rise times (changes from dark to light shades) where they ranged up to 15 - 17ms. The overdrive impulse was being very modestly applied here and the result was an average response time of 7ms G2G, with no overshoot really. Not slow of course, but TN Film panels can do better.

Indeed pushing the screen up to the 'Normal' setting brought about some obvious improvements both in our measurements, and in visual tests. The average response time was now measured at 4.2ms G2G, fixing some of those slow rise times quite well and still without introducing any real overshoot which was great news. Some transitions even reached as low as 1.1ms G2G in this mode, under the 2ms G2G spec from LG in fact.

Pushing the setting up to the maximum 'Fast' mode did improve the response times a bit, with an average 2.7ms G2G now being measured. However, it was at the expense of some large levels of overshoot, which were also very noticeable and obvious in visual tests. We would recommend sticking with the 'normal' mode which was optimal on this screen when it came to pixel response times.

Refresh Rate and FreeSync

This screen supports high refresh rates up to 240Hz natively thanks to its modern high refresh rate TN Film panel, which is far beyond what is currently possible from other panel technologies like VA and IPS. High refresh rates bring about noticeable and obvious benefits in fast moving content and put these screens ahead of common 60Hz models when it comes to fast gaming. You get support for higher frame rates for a start, which is important for competitive gaming. Because of the way LCD screens operate, refresh rate also has a direct relation to how the human eye perceives motion blur. The higher the refresh rate, the less motion blur you will see from the screen. So the ability to support beyond 60Hz is very welcome when it comes to improving the gaming experience.

There are obvious improvements in motion clarity when you move from a standard 60Hz screen to 120 - 144Hz, but what about going all the way to 240Hz? Does it make much difference? The answer is - it depends. If you are able to push the high frame rates to the screen consistently and have a powerful enough system to run at 1920 x 1080 @ 200 - 240Hz then you will see some benefit from the increased refresh rate compared with 120 - 144Hz. You do get some improvements again in motion clarity and reduction in perceived motion blur thanks to the higher frame rate and refresh rate. They aren't as significant as that first jump from 60Hz to 120Hz, but you can still see them in practice. 240Hz is more aimed at competitive, fast gaming requirements and those wanting the absolute fastest screen you can get. A fast TN Film panel like this with a very fast response time and a super-high refresh rate will offer you some of the best gaming performance currently available from the monitor market.

One thing to keep in mind also is whether the pixel response times are fast enough to keep up with the frame rate demands of the high refresh rate. To deliver 120Hz for instance, a new frame is sent to the screen every 8.3ms, which means that response times need to be consistently under this to keep up. If they're not, then you end up with some added smearing on fast moving content. For a 240Hz refresh rate you need response times to be under 4.17ms to keep up (1000 ms / 240 Hz = 4.17ms). On the 27GK750F the response times were just about fast enough overall to keep up with the refresh rate demands.

The screen supports AMD FreeSync for variable refresh rates, with a nice wide range of 48 - 240Hz supported. This helps remove tearing and stuttering when you have varying frame rates in gaming, without adding the lag that traditional Vsync would introduce. The benefits of AMD FreeSync are well documented so we won't go in to those here, but it's a big benefit to have that support when it comes to gaming. To power a screen at 1920 x 1080 resolution and 240Hz refresh rate will need a high end system and graphics card, so the presence of FreeSync to support dipping frame rates and less powerful systems is very useful. In fact it's probably a good thing that the resolution is limited to 1080p here as well, as anything higher would add even more demand on your system and graphics card.

 

Detailed Response Time Measurements
Response Time mode = Normal

   

Having settled on the 'normal' response time mode in our earlier measurements and visual tests we carried out a more thorough set of measurements across a wider range of pixel transitions. The average G2G figure was measured at 4.7ms which was good thanks to the fast, high refresh rate TN Film panel. The response times were as fast as 1.1ms on some transitions, but a few of them were also a little slower up to around 10 - 12ms. This was on changes from black or very dark shades to brighter shades but only a few transitions were affected. The fall times (changes from lighter to darker shades) were on average quite a lot faster than the rise times (changes from darker to lighter shades). Only a very small amount of overshoot crept in on a couple of transitions, mainly when changing between the lighter grey shades and white. This lead to some skewing of light colours on white backgrounds but nothing too major. Overall the response times were just about fast enough to cope with the high frame rate demands of 240Hz, where a new frame needs to be drawn every 4.17ms.

Gaming Comparisons

We have provided a comparison of the LG 27GK750F against many other gaming screens that we have tested. The screen was slightly slower when it came to pixel response times (at 4.7ms G2G average) than the smaller 24.5" sized 240Hz screens we've previously tested, the Asus ROG Swift PG258Q (3.4ms G2G with similar low levels of overshoot to the LG) and the AOC AGON AG251FZ (2.6ms G2G but with higher, moderate levels of overshoot). Some of the other TN Film panels shown here can also reach down a little lower than the 27GK750F, but at the expense of introducing higher levels of overshoot which is not ideal. For instance the very popular Asus ROG Swift PG278Q (2.9ms G2G) and BenQ XL2730Z (3.4ms G2G). We prefer ourselves to have a more balanced overdrive without much overshoot, as the dark trailing that a higher overshoot can introduce can be distracting. It was a good balance we felt here from the 27GK750F.

 

Motion Blur Reduction

Many NVIDIA G-sync capable screens feature a blur reduction option called Ultra Low Motion Blur (ULMB), which offers a strobing backlight system designed to help reduce perceived motion blur of LCD displays. This is a inherent part of the G-sync module and offered on the majority of G-sync displays. Of course the 27GK750F is an AMD FreeSync screen instead, and there is no blur reduction feature included inherently with that technology as there's no additional module like there is with G-sync. However, LG have added their own strobed backlight to this display which they've dubbed '1ms Motion Blur Reduction' and this is explained above in their graphic. They describe the feature as follows: "1ms Motion Blur Reduction allows gamers to enjoy the precision and accuracy needed to play at a high level. With a response time that is virtually 1ms, blurring and ghosting are dramatically reduced to make the in-game action smoother and gamer�s reactions more precise."

The 1ms response time figure is for advertising purposes really. The underlying pixel response times are not changing and we measured around 4.7ms G2G average earlier on in this review - although some transitions did reach down to around 1ms in fact. However, the strobing means that the human eye will perceive less motion blur and it is considered the equivalent of a 1ms response time as a result.

This feature is not linked to FreeSync like ULMB is to G-sync, it is added separately to the screen and so in theory could be used on any display which supports a suitable refresh rate. It's not that common to have a blur reduction mode available on a FreeSync screen so it's really nice to see it included here. We've had an in depth look at these blur reduction backlights in the past and would recommend a read of our detailed article if you want to know more about how they work, and what they can offer.

On the 27GK750F the blur reduction backlight option is available when running at either 120Hz, 144Hz or 240Hz refresh rate. The option is not available at lower 75Hz or 60Hz modes, and also not supported when using FreeSync. So you're not going to be able to use this feature for external games consoles which operate at 60Hz for instance. This is the first screen we've tested where a blur reduction backlight is supported at these higher refresh rates including 240Hz. Even the Asus ROG Swift PG258Q with a native 240Hz refresh rate only allowed use of the blur reduction mode up to 144Hz maximum.

1ms Motion Blur Reduction backlight cycling, 240Hz (scale = 5ms)

We tested the strobing backlight at all supported refresh rate settings. Above is the graph at 240Hz which shows that the backlight is cycled on and off every 4.17ms in sync with the refresh rate. The backlight is turned on for 1.17ms and then turned off for 3ms of each cycle which helps to hide parts of the pixel transitions and improve the perceived motion blur. This has the knock-on effect of significantly reducing the brightness of the screen, as recorded in the next section.

A similar story at 120Hz where it is cycled on and off every 8.33ms and at 144Hz where it is cycled every 6.94ms in sync with the refresh rate. This is normal behaviour for these kind of backlights. There is no further control over the strobe length or strobe timing offered on the screen, so it's just a simple off/on strobing available here. Given this operates only at high refresh rates above 120Hz, we didn't see any noticeable flickering to the naked eye, which can sometimes be an issue if you =use these features at lower refresh rates like 85Hz for instance.

Brightness Range - 240Hz Refresh Rate

We wanted to test the brightness range available when using the Blur Reduction mode at the maximum 240Hz. The table above confirms the range available through that control. You can achieve a slightly brighter display (around 247 cd/m²) if you use the feature at 120Hz or 144Hz since the strobes are less frequent, but it's not a significant amount.

Unfortunately the brightness setting when Motion Blur is turned on is the same as when it's off, so you might have to adjust the brightness control each time you enable or disable the setting. Although some of the preset modes have this feature enabled by default, and you can customise the brightness setting in each of those if you want.

Remember that we measured the normal brightness of this screen as reaching up to 452 cd/m² in general mode which was very bright, and the minimum 0% brightness setting did not reach down to very low levels, only to around 143 cd/m². This was somewhat restrictive for general uses, but it looks like this has been done to allow support for reasonable luminance when using the Motion Blur reduction strobing backlight. At 240Hz you can reach up to a decent 199 cd/m² at maximum brightness, and down as low as 69 cd/m² at minimum brightness. Had the backlight not as been as bright in normal use, it would not have been possible to achieve these decent levels of luminance when using the blur reduction mode in gaming. At 240Hz the backlight is being turned off 240 times per second, and is actually in an 'off' state for around 72% of the time, so you can understand how this would impact the luminance output of the screen so much.

Maximum Blur Reduction Brightness - Display Comparison

For ease of reference we have also provided a comparison table below of all the blur reduction enabled displays we've tested, showing their maximum luminance before blur reduction is turned on (normal mode) and their maximum luminance with the feature enabled. This will give you an idea of the maximum brightness you can expect from each model when using their blur reduction feature, if that is important to you. A lot of people want a brighter display for gaming and sometimes the relatively low maximum luminance from blur reduction modes is a limitation.

These comparisons are with the refresh rate as high as is available for the blur reduction feature to function. For most this is at 100 - 144Hz. You can achieve a slightly brighter display if you use the feature at compatible lower refresh rates since the strobes are less frequent, but it's not a significant amount. That can also introduce more visible flicker in some situations.

Note: Pulse Width setting at max where applicable.
*Note 2: The Acer XB270HU was later updated to include a 120Hz mode, which will produce a slightly darker maximum luminance
 

The 27GK750F showed a good upper luminance when using the Blur Reduction mode, even considering it was being used at a much higher refresh rate compared with the other screens shown here. A lot of blur reduction backlights are criticised for their low luminance, so it was good to see a decent range offered here to make the feature usable.

Blur Reduction Tests

Of course the main thing we want to test is what improvements the Blur Reduction mode offers when it comes to motion clarity and gaming. We were pleased with the results we'd seen from LightBoost backlights when we tested them, and also from the natively supported blur reduction feature on other displays including the other popular gaming models we've tested.

240Hz                            144Hz

Motion Blur Reduction option enabled, upper, middle and lower screen areas of the screen

We used the BlurBusters full-screen TestUFO online motion test and a pursuit camera method to put the feature through its paces. This helps capture an indication of what the human eye would actually see in practice thanks to the pursuit camera.

We were particularly impressed with the results on this screen thanks to the support for 240Hz strobing. This is the first screen we've seen where strobing is supported at this full 240Hz and it showed some excellent performance in practice. Perhaps most noticeable was the very low levels of strobe cross-talk at this setting. Normally when you use a strobed backlight some parts of the screen look very clear and have a sharp image with minimal ghosting, whereas other parts of the screen can look much worse. If you look at the images above at 144Hz on the right you can see what a typical strobing backlight might look like in fact. It was a similar story on the 27GK750F in both the 120Hz and 144Hz supported modes. The middle and lower portions of the screen were much clearer than the top section, showing a clearer image which was easy to track with the eye, and showed low levels of ghosting. In the top area though the timing of the strobe relative to the refresh rate cycle resulted in typical strobe cross-talk issues, where the image actually looked pretty bad and you had high levels of ghosting on the image. This is common on every strobed backlight screen we've seen, where you have to live with some parts of the screen having higher levels of strobe cross-talk than others.

We were pleasantly surprised by the results at 240Hz though where the whole screen seemed to show very low levels of cross-talk, and the image looked clear and sharp in all sections. This is related to the higher frequency of the strobing and the relatively long periods of 'off' state to the backlight, and it had been set up very nicely here by LG. If you are able to power the screen sufficiently and achieve suitable frame rates, we would certainly recommend running at 240Hz if you want to use the Motion Blur Reduction backlight. This was probably the most well-implemented strobing backlight we've seen to date.

Additional Gaming Features

• Aspect Ratio Control - the screen has 3 options for hardware level aspect ratio control options, with settings for 'full wide', 'original' and 1:1 pixel mapping offered. That's useful as there's settings to match the input aspect if it is different to the native 16:9 of this screen.

• Preset Modes - There are a series of preset modes available in the menu for different gaming uses, including FPS and RTS games. Many of the settings are locked in the FPS and RTS preset modes including black stabilizer, response time, 1ms Motion Blur activation, gamma, colour temperature and the RGB channels. These are all set at differing values depending on the preset mode. You can still control things like the brightness of the screen in all modes and each one will save your setting thankfully. If you want more flexibility to set the screen up to your liking, there are also 2 fully customisable 'gamer' preset modes which is useful.

• Black stabilizer - this setting allows you to adjust the gamma curve to bring out more detail in darker content. This might be a useful setting to play with depending on your gaming environment and the content you're viewing.

Lag

We have written an in depth article about input lag and the various measurement techniques which are used to evaluate this aspect of a display. It's important to first of all understand the different methods available and also what this lag means to you as an end-user.

Input Lag vs. Display Lag vs. Signal Processing

To avoid confusion with different terminology we will refer to this section of our reviews as just "lag" from now on, as there are a few different aspects to consider, and different interpretations of the term "input lag". We will consider the following points here as much as possible. The overall "display lag" is the first, that being the delay between the image being shown on the TFT display and that being shown on a CRT. This is what many people will know as input lag and originally was the measure made to explain why the image is a little behind when using a CRT. The older stopwatch based methods were the common way to measure this in the past, but through advanced studies have been shown to be quite inaccurate. As a result, more advanced tools like SMTT provide a method to measure that delay between a TFT and CRT while removing the inaccuracies of older stopwatch methods.

In reality that lag / delay is caused by a combination of two things - the signal processing delay caused by the TFT electronics / scaler, and the response time of the pixels themselves. Most "input lag" measurements over the years have always been based on the overall display lag (signal processing + response time) and indeed the SMTT tool is based on this visual difference between a CRT and TFT and so measures the overall display lag. In practice the signal processing is the element which gives the feel of lag to the user, and the response time of course can impact blurring, and overall image quality in moving scenes. As people become more aware of lag as a possible issue, we are of course keen to try and understand the split between the two as much as possible to give a complete picture.

The signal processing element within that is quite hard to identify without extremely high end equipment and very complicated methods. In fact the studies by Thomas Thiemann which really kicked this whole thing off were based on equipment worth >100,1000 Euro, requiring extremely high bandwidths and very complicated methods to trigger the correct behaviour and accurately measure the signal processing on its own. Other techniques which are being used since are not conducted by Thomas (he is a freelance writer) or based on this equipment or technique, and may also be subject to other errors or inaccuracies based on our conversations with him since. It's very hard as a result to produce a technique which will measure just the signal processing on its own unfortunately. Many measurement techniques are also not explained and so it is important to try and get a picture from various sources if possible to make an informed judgement about a display overall.

For our tests we will continue to use the SMTT tool to measure the overall "display lag". From there we can use our oscilloscope system to measure the response time across a wide range of grey to grey (G2G) transitions as recorded in our response time tests. Since SMTT will not include the full response time within its measurements, after speaking with Thomas further about the situation we will subtract half of the average G2G response time from the total display lag. This should allow us to give a good estimation of how much of the overall lag is attributable to the signal processing element on its own.

Lag Classification

To help in this section we will also introduce a broader classification system for these results to help categorise each screen as one of the following levels:

• Class 1) Less than 8ms / 1 frame lag at 120Hz, or less than 2 frames at 240Hz - should be fine for gamers, even at high levels

• Class 2) A lag of 8 - 16ms / One to two frames at 120Hz - moderate lag but should be fine for many gamers. Caution advised for serious gaming

• Class 3) A lag of more than 16ms / more than 2 frames at 120Hz - Some noticeable lag in daily usage, not suitable for high end gaming

For the full reviews of the models compared here and the dates they were written (and when screens were approximately released to the market), please see our full reviews index.

We have provided a comparison above against other models we have tested to give an indication between screens. The screens tested are split into two measurements which are based on our overall display lag tests (using SMTT) and half the average G2G response time, as measured by the oscilloscope. The response time 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.

We measured a total display lag of only 8.75ms. With approximately 2.35ms of that accounted for by pixel response times we had an estimated signal processing of just 6.40ms, which was very low, and about 1.5 frames at 240Hz. This is in keeping with other gaming screens we have tested. All the G-sync screens we have tested show very low, often next to no input lag thanks to the absence of a scaler and presence of the G-sync module. FreeSync screens can vary a bit, and because many of them feature a scaler you sometimes have lag higher at around 16ms. Thankfully on the 27GK750F, given this is a gaming screen, LG have gone a good job of minimising the lag down to a very low level.

Movies and Video

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

Conclusion

The 27GK750F is obviously aimed at gamers and for that target market we felt that it did very well. There are not many screens on the market with a native 240Hz refresh rate and fast TN Film panel, and most are in the smaller 24.5" size. This is a slightly larger screen at 27" but still offers those top end gaming specs. As well as the 240Hz refresh rate for high frame rate gaming and lower motion blur, the response times were very good, with very little overshoot. AMD FreeSync support ensures fluctuating frames rates are handled well, and there's also very low input lag. Best of all LG have added an additional Motion Blur Reduction backlight to this screen, and that supports high refresh rates including the maximum 240Hz - the first we've seen with that. It worked really well at 240Hz and even helped eliminate the strobe cross talk to provide a clear image across the whole screen area.

Away from gaming there are a few limitations to be aware of. Being a TN Film panel you have to live with known limitations with the technology, particularly with the viewing angles and contrast /colour shifts. The resolution of 1080p on a 27" screen is a little low when you compare to the wide range of 1440p options and you feel that when using the screen for more general office type uses. But you are really making the resolution sacrifice here for the sake of the 240Hz refresh rate. The brightness range is a bit limited at the lower end and it isn't ideal for darker room conditions for non-gaming uses, but on the other hand the high brightness has allowed for a good upper brightness when using the Motion Blur Reduction mode, so again it's a little bit of a trade-off. Default setup of the screen was pretty good, and better than a lot of other TN Film gaming screens we've seen for general uses. For some odd reason calibration seemed to negatively impact contrast ratio though, which being a TN Film panel was not exactly amazing to start with.

We felt this was a very good option if you're after a fast gaming screen and want a display slightly bigger than most of the other 240Hz models out there. Sure, it has some limitations for non-gaming as most gaming screens do, but it does very well for its intended uses for sure.

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