Introduction

It's been a busy time for Dell recently, with all kinds of new models being released in their ever-popular monitor range. We have reviewed their new UltraSharp 24" class models, the U2414H and U2415, and recently their new 27" U2715H. We've got something a bit different from Dell with us now, their new 25" sized U2515H screen. This is the first 25" display we've reviewed and is something other manufacturers are also looking at with their upcoming line-ups. The U2515H offers the same 2560 x 1440 resolution as the wide range of 27" screens on the market today, but on a smaller screen to give you a higher DPI (dots per inch), and importantly also at a much lower retail cost. The U2515H has al almost identical appearance, spec and feature set to the U2414H (23.8" in size) and U2715H (27"), but in an intermediate screen size. It offers a modern IPS panel and all the features and extras we've come to know from Dell's UltraSharp range. We are keen to see if it can offer the same high quality performance as the other sized models.

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Dell U2515H Now Available
 

Specifications and Features

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

 

The U2515H offers a good range of modern connectivity options which are identical to the recent U2414H/U2415/U2715H screens as well. There are 2x HDMI (with MHL), 1x DisplayPort and 1x Mini DisplayPort input interfaces provided for video connections. There is also a DisplayPort out connection for daisy chaining several screens. There is no DVI or D-sub offered here which might be a bit of a pain for older systems and graphics cards. Cables are provided in the box for only DP > Mini DP. We understand from a few reports that you can actually use a DVI to HDMI adapter to output from a DVI graphics card, to HDMI input on the monitor. This might require a dual-link DVI > HDMI converter given the resolution (to be safe at least) and you may need to create a custom resolution from your graphics card as it seems the 2560 x 1440 @ 60Hz is not automatically detected. It does seem to work though, providing compatibility with DVI graphics cards at least. DVI to DisplayPort is more tricky and would require an active adapter which can be quite expensive and may be more hit and miss.

The screen has an internal power supply so there is only the need for a kettle lead power cable (provided). There are several additional features as well for this screen. These include a factory calibration, 5x USB 3.0 ports (1 with battery charging support) and an audio out port. The screen is compatible with Dell's SoundBar as well if you want (sold separately).

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

OSD Menu

Above: OSD control buttons on the bottom right hand edge

The OSD menu is accessed and controlled through a series of 5 touch-sensitive buttons located on the bottom right hand edge of the bezel. There are small grey circles on the bezel marking where the buttons are which are discrete. They don't light up at all, even when pressed. There is a small power LED bar underneath the power button which glows white during use and pulsates white on/off when the screen is on standby. We did find that sometimes the buttons were a little unresponsive when you first press them, but seemed to work better once you were within the menu sections.

Pressing any of the buttons pops up the quick access menu which is shown above. From here by default you have quick access to the preset modes from button 1, input selection (actually shown as brightness/control above) from button 2, the main menu (3) and a button to exit (4). The power on/off button is shown as well, as button 5 above. You can personalize the quick access options here through the main OSD if you want.

The menu is basically identical to the U2415 so we will keep most of the same screenshots we used in that review to save some time. Obviously the model name shows as Dell U2515H at the top, and the resolution notification at the bottom shows as 2560 x 1440 at 60Hz. The rest is largely unchanged, except for the aspect ratio options which we talk about below.

Using the quick access options pops up a smaller menu above specific to that selection. For instance the input selection quick access menu is shown above.

The main menu is split in to 8 sections shown down the left hand side of the screen. The options available in each section are then displayed on the right hand side. The first section is the brightness and contrast menu which is self explanatory.

The second section allows you to change the input being used.

The 'color' menu gives you access to a few options, mainly useful for accessing the preset mode menu. you can also enter into the 'custom color' mode which then allows you to manually alter the RGB channels for calibration.

The preset mode menu is shown above and you can see the 7 options available.

The 'Display' menu has a few useful extra features. This includes the aspect ratio control menu (options for 16:9 wide, 4:3 and 5:4). You can also change the response time setting here. We have updated the screenshot here to be specifically from the U2515H since the aspect ratio options are different here than on the U2415 (which had 16:10 aspect ratio option instead of 16:9).

The 'energy' section allows you to control the power LED and USB ports.

The other sections are self-explanatory really from the pictures above.

All in all the menu was very easy to navigate and well laid out. The control buttons were mostly responsive and sensitive, and the touch-sensitive nature gave them a premium feel. Sometimes when you first try to bring up the menu they required a few presses to get going. There were quite a few options to play around with as well, and the ability to customise the quick access menu was useful. The menu also remembered which section you were last in when you exit which is quite handy.

 

Power Consumption

In terms of power consumption the manufacturer lists typical usage of 35.0W and less than 0.5W in standby. They also list maximum power usage of 87.0W (*) but this is with maximum brightness, Dell SoundBar and USB connected also. We carried out our normal tests to establish its power consumption ourselves.

We tested this ourselves and found that out of the box the screen used 26.3W at the default 50% brightness setting. Once calibrated the screen reached 19.2W consumption, and in standby it used only 0.6W. We have plotted these results below compared with other screens we have tested. The consumption is comparable actually to the other W-LED backlit displays we have tested, with GB-r-LED backlit displays (Dell U2713H, ViewSonic VP2772) using a bit more than most W-LED backlights.

Panel and Backlighting

Panel Part and Colour Depth

The Dell U2515H features an LG.Display LM250WQ1-SSA1 AH-IPS panel which is capable of producing 16.78 million colours. This is LG.Display's new "Neoblade" panel, featuring a borderless design allowing for the ultra-thin bezel. The panel offers an 8-bit colour depth and the part is confirmed when dismantling the screen:

 

Screen Coating

The screen coating on the U2515H is a light anti-glare (AG) offering. It isn't a semi-glossy coating, but it is light as seen on other modern IPS type panels including other recent screens like the U2715H and U2415 for instance. Thankfully it isn't a heavily grainy coating like some old IPS panels feature, including the older U2711 model. 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 some very slight cross-hatching patterns visible on the coating if you looked very closely, but nothing to the extent of what some people find problematic on the U2713HM model.

Backlight Type and Colour Gamut

The screen uses a White-LED (W-LED) backlight unit which has become very popular in today's market. This helps reduce power consumption compared with older CCFL backlight units and brings about some environmental benefits as well. The W-LED unit offers a standard colour gamut which is approximately equal to the sRGB colour space (99% sRGB quoted). Anyone wanting to work with wider colour spaces would need to consider wide gamut CCFL screens or the newer range of GB-r-LED type displays available now. If you want to read more about colour spaces and gamut then please have a read of our detailed article. Dell have wide gamut models available in 24" 1920 x 1200 (U2413), 27" 2560 x 1440 (U2713H) and larger models if you need wide gamut support.

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 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

At 100% brightness a constant voltage is applied to the backlight. As you reduce the brightness setting to dim the backlight a Direct Current (DC) method is used, as opposed to any form of PWM. This applies to all brightness settings from 100% down to 0%. The screen is flicker free as a result.

For an up to date list of all flicker-free (PWM free) monitors please see our Flicker Free Monitor Database.

 

Contrast Stability and Brightness

The brightness control gave us a very good range of adjustment. At the top end the maximum luminance reached 383.45 cd/m² which was high, and even a fair bit higher than the specified maximum brightness of 350 cd/m² from the manufacturer. There was a decent 348.41 cd/m² adjustment range in total, and so at the minimum setting you could reach down to a low luminance of 35.04 cd/m², lower than the specified 50 cd/m² from the manufacturer as well. This should be more than adequate for those wanting to work in darkened room conditions with low ambient light. A setting of 21 in the OSD menu should return you a luminance of around 120 cd/m² at default settings. It should be noted that the brightness regulation is controlled without the need for Pulse Width Modulation, using a Direct Current (DC) method for all brightness settings between 100 and 0% and 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 not quite a linear relationship as the brightness adjustments between settings of 50 and 0 controls a slightly steeper luminance range than settings between 100 and 50.

The average contrast ratio of the screen was excellent for an IPS panel with an average of 1089:1. This was pretty stable across the brightness adjustment range as shown above although at the top and bottom end of the brightness range it did fluctuate a little.

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 the DVI interface, and analysed using an X-rite i1 Pro Spectrophotometer (not to be confused with the i1 Display Pro colorimeter) 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 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

The Dell U2515H comes factory calibrated, showing their focus on providing a high quality product suitable for colour critical work. Like other recent UltraSharp models the screen is packaged with a calibration report unique to your unit, confirming the targets set and met during that process. Here they have factory calibrated the default 'Standard' preset mode to a 2.2 gamma, 6500k white point and with a dE colour accuracy of <3. A copy of the calibration report from our unit is provided below for reference:

Default settings of the screen were as follows:

Dell U2515H - Default Settings / Factory Calibration

  

 

Initially out of the box the screen was set in the default 'standard' preset mode which carries the factory calibration discussed above. The screen was bright as it was set at a default 50% brightness setting. Colour balance and temperature felt good, and you could tell it was a standard gamut screen. We went ahead and measured the default state with the i1 Pro.

 

The CIE diagram on the left of the image confirms that the monitors colour gamut (black triangle) is roughly equal to the sRGB colour space. There is some minor under-coverage in some green and red shades but not by anything significant. Default gamma was recorded at 2.2 average, leaving it with a very minor 1% deviance from the target which was pleasing. White point was measured at 6626k being close to the target of 6500k which was very good and with only a 2% deviance.

 

 

Luminance was recorded at a bright 248 cd/m² which is too high for prolonged general use. The screen was set at a default 50% 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. The black depth was 0.23 cd/m² at this default brightness setting, giving us an excellent (for a IPS panel) static contrast ratio of 1096:1. Colour accuracy was pretty good out of the box with a default dE average of 2.8, although a maximum of 6.3 showed there were some errors. Testing the screen with various gradients showed smooth transitions with no sign of any banding thankfully. There was some slight gradation evident as you will see from most monitors in darker tones. Overall the default setup was good, with the gamma and white point being decent. Looks like the factory calibration does provide a reliable setup for the screen which should be fine for most casual users once they've adjusted the brightness setting.

 

 

We also switched to the 'custom color' mode to test that preset out of the box:

 

Dell U2515H - Default Settings, Custom Color Preset

 

The Custom Color mode was not as reliable and showed a significant difference in the gamma curve. Dark shades had a gamma much lower than the desired 2.2, dropping down to 1.85 and resulting in an average gamma overall of 1.9 (15% deviance from the target). White point was accurate, with a 0% deviance. Colour accuracy had deteriorated a little, with dE average now of only 4.0 being measured. This mode is useful for calibration since you now have access to the RGB channels, but you will need a calibration device to correct the gamma curve. If you don't have one, you would probably be better sticking with the default 'standard' mode and turning the brightness down to a comfortable level. The 'custom color' default mode had a higher contrast ratio (1188:1 here), since by default the RGB channels were all at 100.

 

 

 

 

Calibration

 

We used the X-rite i1 Pro 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.

 

Dell U2515H - Calibrated Settings

   

 

We changed to the 'custom color' preset mode first of all which would give us access to the RGB channels, as well as the brightness and contrast settings which are available in all the modes. All these OSD changes allowed us to obtain an optimum 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 now corrected to 2.2 average, correcting the large 15% deviance we'd seen out of the box in this 'custom color' preset mode. If you're using the 'custom color' mode, you need a calibration tool to correct the gamma curve, which has an average of 1.9 out of the box. The white point was maintained at an accurate level, measured at 6476k (0% deviance). Luminance had been improved thanks to the adjustment to the brightness control and was now being measured at 122 cd/m². This left us a black depth of 0.11 cd/m² and maintained an excellent static contrast ratio (for an IPS panel) of 1138:1. Colour accuracy of the resulting profile was very good, with dE average of 0.4 and maximum of 0.9. LaCie would consider colour fidelity to be very good overall. Testing the screen with various colour gradients showed mostly smooth transitions. There was some slight gradation in darker tones but no banding introduced due to the adjustments to the graphics card LUT from the profilation of the screen which was pleasing. 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. 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 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 good with a gamma and white point within a few % deviance from the targets. Colour accuracy was good at dE 2.8 average, and contrast ratio was excellent for an IPS panel at 1096:1. It is too bright of course, but that's easy to turn down via the brightness setting. If we compare those default settings to the new 27" U2715H model the results are pretty comparable. That had a slightly worse default gamma (2.3 average, 5% deviance) but a slightly better white point (6414k, 1% deviance). Colour accuracy was very similar with dE average of 2.7, although contrast ratio out of the box was not as strong at 928:1. So comparing default screen settings, there's not much to separate the new 2560 x 1440 resolution 25" and 27" models.

 

 

 

The display was very strong when it came to black depth and contrast ratio for an IPS-type panel. With a calibrated contrast ratio of 1138:1 it was the best we had seen to date from this kind of panel technology. It out-did other recent Dell models like the U2415 (1011:1) which was impressive and was quite a lot higher than the 27" U2715H (856:1). Of course it can't compete with VA panel types which can reach over 2000:1 easily, and commonly up to 3000:1, even close to 5000:1 in the case of the Eizo FG2421.

 

Viewing Angles

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

Viewing angles of the U2515H 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 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. All as expected really from a modern IPS panel.

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

On a black image there is a characteristic white glow when viewed from an angle, commonly referred to as IPS-glow. This is common on most modern IPS panels and can be distracting to some users. If you view dark content from a normal head-on viewing position, you can actually see this glow as your eyes look towards the edges of the screen if the screen is of a large size. This is not so much of a problem on a smaller screen like this than it might be on some of the larger displays like the 27" model for instance, but it could still be distracting if you work with a lot of dark content. The IPS glow was normal here for a modern IPS-type panel.

Panel Uniformity

We wanted to test here how uniform the brightness and colour temperature was across the screen, as well as identify any leakage from the backlight in dark lighting conditions. Measurements of the luminance and colour temperature 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. Measurements for colour temperature (white point) were taken using BasICColor software and the i1 Pro spectrophotometer which can more accurately measure the white point of different backlighting technologies. 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

The luminance uniformity of the screen was mostly pretty good. The top corners did seem to drop down in luminance somewhat, ranging down to 104 cd/m² in the most extreme cases. The lower middle was also a little bit brighter than the centrally calibrated point, ranging up to 131 cd/m² in the most extreme case. Around 83% of the screen was within a 10% deviance from the centrally calibrated point which was good.

 

Backlight Leakage

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

As usual 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 very little backlight leakage here with some clouding detected in the top left hand corner. It was not too bad though and hard to pick out with the naked eye, and should not present any major problems in normal use.

 

General and Office Applications

The U2515H is a new screen size we've not tested before, measuring 25" diagonally. We are starting to see a few manufacturers adopt this screen size though and it seems to be attracting a lot of interest in the market. It is a little bit bigger than a 24" model, although noticeably smaller than a 27" we felt during use. What makes this particularly interesting is that the screen still offers the same 2560 x 1440 resolution that the wide range of 27" models provide. Being smaller, it carries a couple of advantages though. Firstly the retail price is more aligned with the 24" models, and is considerably cheaper than the 27" equivalents. For example the Dell 24" U2414H retails for ~£174, the 25" U2515H for ~£254 and the 27" U2715H for ~£416. Secondly, with the large resolution crammed in to a smaller screen size, you get a higher DPI, tighter pixel pitch (0.216mm) and a sharper looking image. It doesn't have the DPI of ultra-HD or 4k displays, but it is a bit different from a 27" model with the same resolution.

The pixel pitch of 0.216 mm is small as a result, and by comparison a standard 16:9 format 24" model has a pixel pitch of 0.2745mm and a 27" model has 0.231mm. Some users may find the small text a little too small to read comfortably, and we'd advise caution if you are coming from a screen where the pixel pitch and text are much larger. We have gotten used to 27" displays with 2560 x 1440 and so the change here, although noticeable, is not extreme. You shouldn't need to worry about operating system or application scaling like you do on 4k displays, as you can just run at the native resolution comfortably and take advantage of the nice real estate offered. You could use scaling options if you found the fonts and texts a bit too small, but if you are going to do that, you might be better off with the larger 2560 x 1440 27" models (e.g. U2715H) so you don't have to give up real-estate. The high resolution is really good for office and general use, giving you a really big area to work with. It is a noticeable upgrade from a 24" 1080p or 1200p resolution for sure. For those wanting a high resolution for CAD, design, photo work etc, this is a really good option. The image was very sharp and crisp and text was very clear. With its WQHD display, you enjoy 77% more desktop space than a full HD screen to spread out your windows and palettes.

The light AG coating of the new AH-IPS panel is certainly welcome, and a very positive change from the older grainy and 'dirty' appearance of older IPS AG coatings, although not used on Dell 27" models since the U2711 about 5 years ago. The wide viewing angles provided by the IPS 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 good in all regards thanks to the pretty decent factory calibration, and we were also pleased with the excellent 1138:1 contrast ratio (after calibration).

The brightness range of the screen was also very good, with the ability to offer a luminance between 383 and 35 cd/m². This should mean the screen is perfectly useable in a wide variety of ambient light conditions, including darkened rooms. A setting of ~21 in the OSD brightness control should return you a luminance close to 120 cd/m² out of the box. On another positive note, the brightness regulation is controlled without the need for the use of the now infamous Pulse-Width Modulation (PWM), and so those who suffer from eye fatigue or headaches associated with flickering backlights need not worry.

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. There is a 'paper' preset mode available from the menu which may be useful if you want to set up the screen for different uses perhaps and made the image much more yellow. There are only 2x HDMI and 2x DisplayPort connections (1 regular, 1 mini) here so connectivity could be considered a little limited for some older systems. We would have liked to have seen DVI and VGA provided as many graphics cards still rely on these options and no one wants to have to go and fork out for an adapter cable really.

The screen offers 5x USB 3.0 ports which can be useful and it was nice to keep this up to date with the modern version. Here, 4 of them are on the underside back with the video connections, and 1 is on the back of the screen (the charging capable port) since the profile of the screen is too thin to really make them easy to include on the edge of the screen.

There are no further extras like ambient light sensors or card readers which can be useful in office environments. There was a great range of ergonomic adjustments available from the stand allowing you to obtain a comfortable position for a wide variety of angles. The VESA mounting support may also be useful to some people as well. Perhaps one of the biggest draws for the U2515H (and other new UltraSharp models) is its ultra-thin bezel and narrow edges. This makes it potentially a great screen for multi-monitor setups and we liked the design of the new screen.

 
Above: photo of text at 2560 x 1440 (top) and 1920 x 1080 (bottom)

The screen is designed to run at its native resolution of 2560 x 1440 and at a 60Hz recommended refresh rate. However, if you want you are able to run the screen outside of this resolution. We tested the screen at a lower 1920 x 1080 resolution to see how the screen handles the interpolation of the resolution, while maintaining the same aspect ratio of 16:9. At native resolution the text was very sharp and comfortable as we've already discussed. When running at a 1080p resolution the text is still sharp, with low levels of blurring. You do lose some screen real-estate as well of course but the image seems to be interpolated well from 1080p sources.

Responsiveness and Gaming

The U2515H is rated by Dell as having a 6ms to 8ms G2G response time, depending on the setting selected, which indicates the panel uses overdrive / response time compensation (RTC) technology to boost pixel transitions across grey to grey changes. There is user control over the overdrive impulse within the OSD menu using the 'Response Time' option. The part being used is the LG.Display LM250WQ1-SSA1 AH-IPS panel. Have a read about response time in our specs section if you need additional information about this measurement.

We will first test the screen using our thorough response time testing method. This uses an oscilloscope and photosensor to measure the pixel response times across a series of different transitions, in the full range from 0 (black) to 255 (white). This will give us a realistic view of how the monitor performs in real life, as opposed to being reliant only on a manufacturers spec. We can work out the response times for changing between many different shades, calculate the maximum, minimum and average grey to grey (G2G) response times, and provide an evaluation of any overshoot present on the monitor.

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.
 

Response Time Setting Comparison

The U2515H comes with a user control for the overdrive impulse available within the OSD menu in the 'display' section as shown above. This isn't something Dell used to provide, but they've started to feature it on their new models which is pleasing. Previously the user was reliant on the factory setup and often this has lead to issues with overshoot on some models (e.g. Dell U2413, U2713H, U3014). There are two options available here in the menu, for 'normal' and 'fast' modes.

First of all we carried out a smaller sample set of measurements in both of the 'Response Time' settings. These, along with various motion tests allowed us to quickly identify which was the optimum overdrive setting for this screen.

First we tested the screen with the Response Time option set to 'Normal' which according to Dell should have an 8ms G2G response time. Response times varied somewhat, with some transitions being a little slower at around 11 ms, and others reaching down to 6 - 7 ms. Overall we measured an average 8.2ms G2G response time which was as good as we have seen to date for an IPS panel. Keep in mind this is based on a small sample set, so the actual overall average response time might vary when we come to measure a wider range of transitions. In this response time mode there were a couple of cases where overshoot was quite high but not a massive amount overall. A decent result from the 'normal' response time mode.

With the Response Time setting now switched up to the 'Fast' mode, response times had improved a little to 7.8ms G2G average. However, this was at the cost of some noticeable overshoot which was a shame. The overdrive was being applied a bit too aggressively here, trying to reduce response times further, but introducing too many side-effects sadly. The 'Normal' mode was optimum on this model we felt as the slight improvement in response times wasn't worth the high levels of overshoot on more transitions.
 

If we take some test photos using the PixPerAn tool you can make some further visual comparisons between the overdrive 'Response Time' settings. With Response Time set to 'normal' the moving image showed some low levels of motion blur, but nothing too major. There was no sign of any overshoot artefacts in this mode which was pleasing. When you switch to the 'fast' setting, the blurring is reduced a little as response times are boosted. Some slight overshoot is evident in these particular colour transitions but nothing major here only some slight dark trailing. We know from our oscilloscope measurements above that some transitions do show significant levels of overshoot on quite a few transitions so we still prefer the 'normal' mode.

 

More Detailed Measurements - Response Time = Normal

Having established that the Response Time 'Normal' mode seemed to offer the best response/overshoot balance we carried out our normal wider range of measurements as shown below:

The average G2G response time was more accurately measured at 9.3ms which was good for an IPS panel overall. Some transitions were faster at 6 - 7 ms minimum, particularly when changing to white (x > 255) or to black (x > 0). The rise and fall time average were very similar as well.

There was very little overshoot as well in this Response Time mode, with only a couple of transitions showing anything significant. The overdrive impulse was being applied well and in a controlled fashion which was pleasing. We had seen that boosting the RTC in the 'Fast' mode just led to too much overshoot.

Transition: 0-50-0 (scale = 20ms)

The above graph gives an example of the most severe overshoot with response time set to 'normal'. On the rise time in this example, the brightness overshoots the desired level here by 25.9%. Nearly all other transitions showed no overshoot at all which was very good.

Display Comparisons

The above comparison table and graph shows you the lowest, average and highest G2G response time measurement for each screen we have tested with our oscilloscope system. There is also a colour coded mark next to each screen in the table to indicate the RTC overshoot error, as the response time figure alone doesn't tell the whole story.

The response time performance of the U2515H using the 'Normal' Response Time setting was good overall for an IPS-type panel. With an average G2G response time of 9.3ms measured, it was a little slower than our reference point IPS screen, the Dell U2415 (8.6ms G2G). That represented about as good as you can get from modern IPS response times to date, without introducing much in the way of overshoot at all. The 'Fast' Response time mode pushed pixel transitions faster, but did result in some significant overshoot so should probably be avoided. Some IPS models can reach lower response times, like the Dell U2713H for instance (7.2ms) but not without the cost of very high overshoot. In practice there was not much really to separate any of the recent Dell models, with the U2515H being pretty comparable to the U2414H (8.9ms) and U2715H (9.9ms). Modern TN Film panels are still much faster, reaching down to 2.9ms for instance in the example of the new Asus ROG Swift PG278Q (with moderate overshoot).

 

The screen was also tested using the chase test in PixPerAn for the following display comparisons. As a reminder, a series of pictures are taken on the highest shutter speed and compared, with the best case example shown on the left, and worst case example on the right. This should only be used as a rough guide to comparative responsiveness but is handy for a comparison between different screens and technologies as well as a means to compare those screens we tested before the introduction of our oscilloscope method.

25" 8ms G2G LG.Display AH-IPS (Response Time = Normal)

In practice the Dell U2515H performed best with Response Time set to 'normal'. There were low levels of motion blur and no ghosting visible, with the moving image looking pretty sharp. Thankfully no overshoot was detectable at all which was pleasing as well.

25" 8ms G2G LG.Display AH-IPS (Response Time = Normal)

27" 8ms G2G LG.Display AH-IPS (Response Time = Normal)

24" 8ms G2G LG.Display AH-IPS (Response Time = Normal)

23.8" 8ms G2G LG.Display AH-IPS

Comparing the U2515H against the other recent UltraSharp screens showed very comparable performance overall. The higher resolution 25" and 27" models were ever so slightly slower than the 24" models, and had a bit of minor overshoot on a few transitions. Nothing significant to separate the four models here though in day to day use.

25" 8ms G2G LG.Display AH-IPS (Response Time = Normal)

27" 1ms G2G AU Optronics TN Film @ 144Hz (OD = Normal)

27" 1ms G2G AU Optronics TN Film + 144Hz (AMA = High)

23.5" 4ms G2G Sharp MVA + 120Hz

We've also included a comparison above against 3 very fast 120Hz+ compatible screens we have tested. The other screens shown here are all aimed primarily at gamers and have various features and extras which make them more suitable overall for gaming. Firstly there is a comparison against the Asus ROG Swift PG278Q with its 144Hz refresh rate and fast response time TN Film panel. This showed very fast pixel response times and smooth movement thanks to its increased refresh rate. You are able to reduce the motion blur even more through the use of the ULMB strobed backlight as well if you need to. In other related areas this screen also supports NVIDIA's G-sync technology. There was some slight overshoot noticeable on the Asus but nothing major.

Then there is a comparison against the BenQ XL2720Z with another very fast TN Film panel and 144Hz refresh rate. This showed very low levels of motion blur, but some dark overshoot was introduced as a side-effect as you can see. This screen even includes a native Blur Reduction mode to help eliminate further perceived motion blur.

Lastly there is the MVA based Eizo FG2421 screen with a fast response time (especially for the panel technology being used) and 120Hz refresh rate support. There is also an additional 'Turbo 240' motion blur reduction mode which really helps reduce the perceived motion blur in practice.

While these pixel response tests from PixPerAn give one view of the performance of the panel, there is something else going on as well here which can't be picked out by the camera. All of these other gaming models are running at 120Hz (or higher) refresh rates, which allows for improved 120fps+ frame rates and in some cases the support of 3D stereoscopic content as well. This can really help improve smoothness and the overall gaming experience so these screens still have the edge when it comes to fast gaming. Any additional extras to reduce perceived motion blur can also have a real benefit in practical terms, and again not easy to pick out with this camera method.

The overall gaming performance of the Dell U2515H was good and we were pleased with what Dell have done with the response time control on these new UltraSharp range models. The two response time settings allow you to choose the best option for your needs. The 'normal' mode was our preferred option, giving a reasonably fast (for IPS) response time of 9.3ms G2G, without introducing any significant overshoot. It is a screen lacking higher refresh rate support or any advanced gaming features like blur reduction modes or G-sync/FreeSync, but as a general screen with decent IPS gaming performance, it's decent. It was pretty comparable at the end of the day with the 24" and 27" equivalents which is not a bad thing at all. The 27" U2715H offers a larger screen size so might provide a little more immersion in gaming than this smaller 25" screen, but the cost is quite a bit higher.
 

Additional Gaming Features

Aspect Ratio Control - Like the U2414H and U2715H models, the U2515H has 3 options for aspect ratio control through the OSD 'Display' menu as shown above. There are options for wide 16:9, 5:4 and 4:3 only. There is no 1:1 pixel mapping mode specifically but given a lot of content from external devices is 16:9 aspect ratio by default, the native aspect of the screen can at least accommodate that nicely. You will have to put up with the screen interpolating 1080p content up to the full size of the screen when using an external device, as you can't use any kind of 1:1 scaling option on this model.

Preset Modes - There is a specific 'game' available in the OSD which appears to make the image a little cooler than our calibrated custom mode. It gives you access to the dynamic contrast ratio control if you want to use it as well.



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 16ms / 1 frame lag - should be fine for gamers, even at high levels

• Class 2) A lag of 16 - 32ms / One to two frames - moderate lag but should be fine for many gamers. Caution advised for serious gaming and FPS

• Class 3) A lag of more than 32ms / more than 2 frames - 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.

The screen showed a total average display lag of 13.7 ms as measured with SMTT 2. Taking into account half the average G2G response time at 4.65ms ('Normal' Response Time setting), we can estimate that there is ~9.05 ms of signal processing lag on this screen. This is nice and low and should not present any problems for gaming, even playing fast FPS games. It's ever so slightly more than the U2415 and U2715H models, but only by ~2ms so nothing to worry about.

Movies and Video

The following summarises the screens performance in video applications:

• 25" screen size makes it a fairly small option nowadays for an all-in-one multimedia screen, much smaller than LCD TV's and many larger format desktop monitors which are now emerging. The 27" U2715H would offer you a slightly bigger screen for movies.

• 16:9 aspect ratio is well suited to videos and movies, leaving you with smaller/no borders on DVD's and wide screen content at the top and bottom than on a 16:10 aspect display.

• 2560 x 1440 resolution can support full 1080 HD resolution content.

• Digital interfaces support HDCP for any encrypted and protected content

• HDMI and DisplayPort connections available. Nice to see HDMI connectivity included for modern DVD players, Blu-ray, consoles etc. 2 HDMI ports are available on this model. MHL support if you want to play content mirrored from your mobile devices.

• Cables provided in the box for DisplayPort to Mini DisplayPort only, no HDMI cable is provided.

• Light AG coating provides clear images with no major graininess, and without the unwanted reflections of a glossy solution.

• Wide brightness range adjustment possible from the display, including high maximum luminance of ~383 cd/m² and a good minimum luminance of 35 cd/m². This should afford you very good control for different lighting conditions. Contrast ratio remains stable across most of that adjustment range as well and is excellent for an IPS-type panel. Brightness regulation is controlled without the need for PWM and so is flicker free at all settings which is pleasing.

• Black depth and contrast ratio are excellent for an IPS-type panel at 1138:1 after calibration. Detail in darker scenes should not be lost as a result.

• There is a specific 'movie' preset mode available for movies or video in the OSD which looked a lot cooler and more blue than our calibrated custom mode.

• Good pixel responsiveness which can handle fast moving scenes in movies without issue. No overshoot issues when sticking to the 'normal' response time mode which is great news.

• Wide viewing angles from IPS panel technology meaning several people could view the screen at once comfortable and from a whole host of different angles. White glow from an angle on black content may be problematic to some users and is common for IPS panel technology.

• No real backlight leakage on our sample which is good.

• Wide range of ergonomic adjustments available from the stand, allowing you to adjust the screen to suit varying viewing positions.

• No integrated stereo speakers offered on this model, but it is compatible with Dell's SoundBar if you want. There is also an audio out connection if you want to connect to headphones or separate speakers when sending sound to the screen over HDMI.

• Hardware aspect ratio control options should be adequate given the default aspect ratio of the screen is 16:9. Additional 5:4 and 4:3 modes offered as well.

• Picture By Picture (PbP) or Picture In Picture (PiP) are not available on this model.
  
   

Conclusion

Readers won't be disappointed to hear that the U2515H compares very well to the other recent Dell UltraSharp screens. It is very similar overall to the smaller 24" U2414H / U2415 and 27" U2715H models. The feature set, spec, connections and design are basically identical which make it an interesting intermediate screen size.

Performance wise the default setup and factory calibration were good, although you will want to stick with the 'standard' mode unless you have a calibration device. We were impressed with the high contrast ratio for an IPS-type panel as well, outdoing the 27" U2715H by a fair amount. Response times were low for an IPS panel and there was pretty minimal overshoot too. Signal processing lag was also nice and low, keeping in line with the other recent UltraSharp screens. Dell seem to have IPS gaming refined at the moment with the current range of 60Hz panels. The light AG coating and flicker free backlight were very welcome, again much like on the other new models.

The most attractive thing about the new U2515H is its price point, being only slightly more expensive than the 24" models, but offering a higher 2560 x 1440 resolution. It's also quite a lot cheaper than the 27" equivalents so it's bound to be a popular screen. The pixel pitch is small, although we didn't find it a problem for day to day use without any operating system scaling. We are used to using the 2560 x 1440 27" models though, so we would just advise some caution if you're coming from a larger pixel pitch screen. It might take a bit of getting used to, but the DPI is actually pretty nice on this size screen we felt. As long as you don't mind the slightly smaller screen size and smaller fonts, the U2515H is an excellent screen and at such a lower cost than the U2715H it's a great option.

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Dell U2515H Now Available