Introduction

Dell's UltraSharp range of screens has always been popular and the 24" models have probably been at the fore front of this interest ever since their 2405FPW screen was released in 2004 and was probably the first "affordable" 24" model on the market. At the time, 17 and 19" screens were the norm, and the 2405FPW was a massive screen upgrade. It's 1920 x 1200 resolution and S-PVA panel were new and exciting and it seemed that screens would never need to be any bigger. Of course things have changed in the last 10 years or so, and 24" is pretty small by modern standard. Nevertheless the relatively low cost and decent specs of 24" screens keep them popular with many buyers and Dell continue to develop their 24" models every year.

In the 24" space, one debate which continues to rage on is whether a 16:10 aspect ratio is better than a 16:9 aspect. 16:9 has become increasingly popular as a 1920 x 1080 resolution is standard for a lot of content nowadays. Panel manufacturers have invested more in 16:9 aspect ratio panels, but there are still those out there who prefer the slightly bigger (vertically) 16:10 1920 x 1200 resolution for office and general work.

Dell have offered 16:10 24" models since the 2405FPW was released, following it up with the 2407WFP, 2407WFP-HC, 2408WFP, U2410, U2412M and most recently the U2413. There have been some fundamental changes in specs and positioning of these models as well. If we focus on the most recent 16:10 aspect models you can immediately spot some significant differences. The U2412M released in 2011 was aimed at general multimedia and all-round uses. It had a standard gamut W-LED backlight and 16.7m colour depth for instance and no fancy extra features beyond Dell's normal decent range of ergonomic and connectivity options. The U2413 in contrast, released a year later was aimed at semi-professional users primarily. It had a wide colour gamut GB-r-LED backlight, 1.07b colour depth, hardware calibration and uniformity compensation feature. It has a few other fancy extras like a card reader, touch sensitive controls and PiP/PbP support. Two very different screens really in specs and performance, and both still readily available today as a result.

At the same time, Dell have started to introduce some 16:9 models into their monitor range. In the 24" UltraSharp range (well, 23.8", but near enough) is the U2414H which was released at the beginning of 2014 and really impressed us as an excellent all-round display with some noticeable improvements over the U2412M, as long as you didn't specifically want the 16:10 aspect ratio of the U2412M model. This year Dell have updated their 16:10 aspect ratio offering with the newly released U2415. This screen is designed to be a replacement for the aging U2412M screen, sticking with the standard gamut backlight and more general features than the semi-professional grade U2413. As such, the U2413 will still be available alongside the new U2415 if you specifically need some of the advanced features offered there. Dell have however beefed up some of the extras on the U2415 compared with the old U2412M. There's a factory calibration provided, USB 3.0, MHL, new connectivity options, touch sensitive controls and a new ultra-thin bezel design. We are keen to see if the U2415 can offer some of the improvements that we saw from the U2414H model, but in a 16:10 aspect ratio size.

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Specifications and Features

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

The U2415 offers a good range of modern connectivity options. 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. Although a DVI > HDMI cable would be an easy option if you've only got DVI output and no DisplayPort or HDMI. Cables are provided in the box for only DP > Mini DP.

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.

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.

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.

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 16:10 wide, 4:3 and 5:4). You can also change the response time setting here.

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 responsive and sensitive, and the touch-sensitive nature gave them a premium feel. There were quite a few options to play around with as well, and the ability to customise the quick access menu was useful.

 

Power Consumption

In terms of power consumption the manufacturer lists typical usage of 23.0W and less than 0.5W in standby. They also list maximum power usage of 75.0W (*) 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 20.0W at the default 75% brightness setting. Once calibrated the screen reached 13.6W consumption, and in standby it used only 0.5W. 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 U3014, U2713H, ViewSonic VP2772) using a bit more than most W-LED backlights.

Panel and Backlighting

Panel Part and Colour Depth

The Dell U2415 utilises an LG.Display LM240WUA-SSA1 AH-IPS panel which is capable of producing 16.78 million colours. We have not been able to verify via the panel spec sheet as to whether this is a true 8-bit module or a 6-bit+FRC panel, but we expect the latter given most of the current standard gamut IPS panels used today are 6-bit+FRC, especially in this size range. This is a measure commonly taken on modern IPS panels, and the FRC algorithm is very well implemented to the point that you'd be very hard pressed to tell any difference in practice compared with an 8-bit panel. The panel is confirmed when dismantling the screen

Screen Coating

The screen coating on the U2415 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 the Dell U2414H for instance. Thankfully it isn't a heavily grainy coating like some old IPS panels feature, including the older U2412M 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 no cross-hatching patterns visible on the coating.

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.

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

0% zoomed vertical scale

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 very low amplitude slight oscillation is introduced but it is not a Pulse Width Modulation switching. The amplitude of this oscillation is so low that you can only really pick it up when changing the vertical scale down to 50 mV, as shown in the last image zoomed in. It is operating also at a very high 1200 Hz frequency. We are only including it here for completeness really, and this should not represent any issue at all for any user. The screen can still be classified as flicker free in our view, and PWM is not used for backlight dimming at any brightness setting.

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 335 cd/m² which was high, and even a fair bit higher than the specified maximum brightness of 300 cd/m² from the manufacturer. There was a decent 308 cd/m² adjustment range in total, and so at the minimum setting you could reach down to a low luminance of 27 cd/m². This was even lower than the advertised 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 36 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 a linear relationship as the brightness adjustments between settings of 100 and 70 control a slightly steeper luminance range.

The average contrast ratio of the screen was very good for an IPS panel with an average of 1015:1. This was pretty stable across the brightness adjustment range as shown above although at the lowest brightness settings 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 U2415 comes factory calibrated, showing their focus on providing a high quality product suitable for colour critical work. This is similar to what they offer from the 16:9 format U2414H model as well, although the measurement criteria is a little better here in fact. The screen is packaged with a calibration report unique to your screen, 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 (the U2414H had dE <4 target). A copy of the calibration report from our unit is provided below for reference:

Default settings of the screen were as follows:

Dell U2415 - 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 75% brightness setting. Colour balance 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 over-coverage in some red shades, and some minor under-coverage in some green shades but not by anything significant. Default gamma was recorded at 2.3 average, leaving it with a small 4% deviance from the target of 2.2 which was reasonable. White point was measured at 6393k being close to the target of 6500k which was very good and with only a 2% deviance.

 

Luminance was recorded at a bright 218 cd/m² which is too high for prolonged general use. The screen was set at a default 75% 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 0.21 cd/m² at this default brightness setting, giving us a very good (for a IPS panel) static contrast ratio of 1017:1. Colour accuracy was pretty good out of the box with a default dE average of 2.2, and maximum of 5.1. 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 very reasonable. Looks like the factory calibration does provide a reliable setup for the screen which should be fine for most casual users.

 

 

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 U2415 - 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 4% deviance we'd seen out of the box. The white point was also corrected to the target, now measured at 6499k, correcting the minor 2% deviance out of the box. Luminance had been improved thanks to the adjustment to the brightness control and was now being measured at 119 cd/m². This left us a black depth of 0.12 cd/m² and maintained a very good static contrast ratio (for an IPS panel) of 1011:1. Colour accuracy of the resulting profile was very good, with dE average of 0.3 and maximum of 0.7. 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 2.2 average, and contrast ratio was strong for an IPS panel at over 1000:1. It is too bright of course, but that's easy to turn down via the brightness setting.

 

 

The display was strong when it came to black depth and contrast ratio for an IPS-type panel. With a calibrated contrast ratio of 1011:1 it was impressive for this technology. 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 Foris FG2421.

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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 U2415 were very good as you would expect from an IPS panel. Horizontally there was very little colour tone shift until wide angles past about 45°. A slight darkening of the image occurred horizontally from wider angles as you can see above as the contrast shifted slighting. Contrast shifts were slightly more noticeable in the vertical field but overall they were very good. The screen offered the wide viewing angles of IPS technology and was free from the restrictive fields of view of TN Film panels, especially in the vertical plane. It was also free of the off-centre contrast shift you see from VA panels and a lot of the quite obvious gamma and colour tone shift you see from some of the modern AMVA and PVA 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. This is not so much of a problem on a smaller 24" screen than it might be on some of the larger displays available today, but could still be distracting if you work with a lot of dark content. The IPS-glow was more pronounced than we had seen from the U2414H, but on the U2415 it was pretty standard for an IPS 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 pretty good overall. The upper right hand region seemed to be a little lighter than the lower left hand region, but not by much. In the upper right hand area the luminance ranged up by 5.51% (127 cd/m² maximum) compared with the centrally calibrated 120 cd/m² point. Along the lower left hand edge the luminance reached down to 107 cd/m² minimum (-12.15%). Overall around 90% of the screen remained within a 10% deviance of the calibrated central point.

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 pretty much no backlight leakage here at all. A very slight amount was detected along the upper left hand edge, but it was barely noticeable at all. A pleasing result from the U2415 here.

 

General and Office Applications

The 1920 x 1200 resolution and 24.1" screen size give a nice decent area in which to work and the vertical resolution is a little more than the range of 16:9 aspect 24" models (1920 x 1080) out there in the market. A lot of people prefer this extra vertical area and it is useful for office applications we think. You may want to consider the fact that high resolution 27" 2560 x 1440 models are becoming increasingly available and so the difference in desktop size is certainly noticeable coming from a 27" screen like that. Nevertheless, the 24" 1920 x 1200 resolution should be adequate for many users. The screen offered a comfortable 0.27mm pixel pitch which delivered easy to read text at a nice size, in our opinion. The resolution is big enough for side by side split screen working as well in many cases although we do find that nowadays a lot of web content needs more than half a screen (i.e. wider than 960 pixels).

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, including that used on the U2412M model. 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 strong 1000:1+ contrast ratio.

The brightness range of the screen was also very good, with the ability to offer a luminance between 335 and 27 cd/m². This should mean the screen is perfectly useable in a wide variety of ambient light conditions, including darkened rooms. A setting of ~36 in the OSD brightness control should return you a luminance close to 120 cd/m² out of the box. If you switch to the 'custom color' mode and want to try our calibrated settings then the brightness setting is detailed in that section of the review. 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. The older U2412M model did use PWM (as did nearly all screens for a long time), so this is another significant change with the new model.

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 more yellowy green. 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. The old U2412M featured only 2x USB 2.0 ports so there is a nice upgrade here. On the U2412M they were located on the side of the screen which is a little easier to access than on the new U2415. 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 U2415 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 1920 x 1200 (top) and 1680 x 1050 (bottom)

The screen is designed to run at its native resolution of 1920 x 1200 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 1680 x 1050 resolution to see how the screen handles the interpolation of the resolution, while maintaining the same aspect ratio of 16:10. At native resolution the text was very sharp and comfortable as we've already discussed. When running at a 1680 x 1050 resolution the text is still pretty sharp, with low levels of blurring. You do lose some screen real-estate as well of course.

Responsiveness and Gaming

The U2415 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 LM240WUA-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 U2415 comes with a user control for the overdrive impulse available within the OSD menu in the 'display' section as shown above. This is rare for a Dell screen as normally you end up being 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 - 12ms, and others reaching down to 5 - 6 ms. Overall we measured an average 8.3ms G2G response time which was very good for an IPS-type panel in fact. It was even a little faster than models like the Dell P2414H and U2414H (8.9ms G2G average) which we take at the moment as a reference point for IPS technology in terms of reaching the fastest response times without introducing any significant overshoot. The U2415 was also pretty much free from overshoot which was very pleasing, and so this could well be a new reference point for us for IPS response times. Let's see if the 'Fast' mode can offer any improvements at all.

With the Response Time setting now switched up to the 'Fast' mode, response times had improved a little to 7.1ms G2G average, not quite as fast as the 6ms G2G spec listed. However, this was at the cost of some noticeable overshoot which was probably too high to make it practical for most uses. The overdrive was being applied too aggressively here, trying to reduce response times further, but introducing too many side-effects sadly. The 'Normal' mode was optimum on this model.

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

The above graph gives an example of the overshoot which manifests itself when you select the 'Fast' response time setting. On the rise time in this example, the brightness overshoots the desired level here by 32.2% which is noticeable to the user.

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 no noticeable ghosting and low levels of motion blur. There was no sign of any overshoot artefacts either. When you switch to the 'fast' setting, the blurring is reduced a little as response times are boosted. Some slight overshoot is evident but nothing major in these specific tests. We know from our oscilloscope measurements above that some transitions do show significant levels of overshoot 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 8.6ms which was very good for an IPS panel overall. Some transitions were faster at 4.6 - 6 ms minimum, particularly when changing to white (x > 255). The rise and fall time average was very similar and so pixel transition times were fairly consistent across the board.

There was pretty much no overshoot as well in this Response Time mode, with only a couple of transitions showing anything at all, and even then, pretty low. The overdrive impulse was being applied well and in a controlled fashion which was pleasing.

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 U2415 using the 'Normal' Response Time setting was very good overall for an IPS-type panel. With an average G2G response time of 8.6ms measured, it was even slightly faster than the Dell P2414H and U2414H (8.9ms). Those models were our reference point before and represented about as good as you can get from modern IPS response times without introducing a significant amount of overshoot. The Dell U2415 is slightly faster and also still free from any noticeable overshoot which was very pleasing. 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. 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.

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

In practice the Dell U2415 performed best with Response Time set to 'normal'. There were relatively low levels of motion blur and no ghosting visible. Thankfully no overshoot was detectable at all which was pleasing.

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

24" 8ms G2G LG.Display e-IPS

23.8" 8ms G2G LG.Display AH-IPS

23.8" 8ms G2G LG.Display AH-IPS

We can first of all compare the performance of the U2415 against 3 other 24" range screens from Dell. The U2415 is designed to replace the old 2011 U2412M model and Dell have done a good job of clearing up the overshoot issues associated with that old model. The U2412M shows some noticeable dark trailing behind the moving image as you can see in the above images, something which can be distracting during gaming and fast moving content. Thankfully Dell have opted to give the user control over the overdrive impulse on the new U2415 and so at the optimum 'normal' response time setting, there is next to now overshoot at all. A definite improvement in pixel response times and gaming performance there.

The U2414H and P2414H 16:9 models had impressed us previously with their pixel transitions, offering response times as fast as you can really get from a modern IPS panel without introducing any noticeable overshoot. The U2415 performs almost identically in practice to the U2414H/P2414H models which is very pleasing.

24" 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 U2415 was very good and we were pleased with what Dell have done with the response time control. This is the first time they've made a response time setting available from the normal OSD and it's nice that they've not forced an overly aggressive overdrive impulse on us like they did on some previous models (e.g. U2413, U2713H). Instead, the two response time settings allow you to choose the best option for your needs. The 'normal' mode was our preferred option, giving a fast (for IPS) response time of 8.6ms G2G, without introducing any real overshoot. A success really for this type of panel technology. It is a screen lacking higher refresh rate support or any advanced gaming features like blur reduction modes or G-sync, but as a general screen with decent IPS gaming performance, it's impressive.
 

Additional Gaming Features

Aspect Ratio Control - The U2415 has 3 options for aspect ratio control through the OSD 'Display' menu as shown above. There are options for 16:10 (wide), 5:4 and 4:3 only. Disappointingly there is no option for 16:9 format which seems very odd given the massive adoption of that aspect ratio and 1920 x 1080 resolutions. There is no 1:1 pixel mapping mode either. This isn't a problem really for PC gaming since you can let the graphics card handle the scaling, but for connection of external devices, games consoles, Blu-ray players etc, the lack of hardware aspect ratio control for 16:9 format content might be a problem. If those are some of your desired uses, you would probably be better going for the very similar, but 16:9 aspect ratio U2414H 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 12.0 ms as measured with SMTT 2. Taking into account half the average G2G response time at 4.3ms ('Normal' Response Time setting), we can estimate that there is ~7.7 ms of signal processing lag on this screen. This is very low and should not present any problems for gaming, even playing fast FPS games.

 

Movies and Video

The following summarises the screens performance in video applications:

• 24" screen size makes it a relatively small option for an all-in-one multimedia screen, much smaller than LCD TV's nowadays.

• 16:10 aspect ratio is not as well suited to videos and movies as 16:9 format models, leaving you with larger borders on DVD's and wide screen content at the top and bottom.

• 1920 x 1200 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 ~335 cd/m² and a good minimum luminance of 27 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 very good 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 very good for an IPS-type panel at 1011:1 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.

• Some slight areas of backlight leakage but nothing major on our sample which is good. Some uniformity variations may be visible on darker movie scenes in darkened room conditions.

• Wide range of ergonomic adjustments available from the stand, allowing you to adjust the screen to suit varying viewing positions. The side to side swivel is too stiff which might be a bit of a pain for viewing movies from a non desk position.

• 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 are limited, and missing 16:9 or 1:1 pixel mapping options. Might be a pain if using external devices to pay movies, but not an issue from a PC of course. Should have included a 16:9 mode really.

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

Conclusion

We had high hopes for the U2415 display after recent Dell models like the P2414H and U2414H had impressed us with their solid all round performance. Thankfully it didn't disappoint. The U2415 is for all intents and purposes a 16:10 version of the U2414H. There's one extra USB port here, but apart from that the connections and functionality are the same. Both offer the new slim bezel design which looks very attractive and is ideal for multi-screen setups. The U2415 had a wider range of backlight adjustments and a slightly higher static contrast ratio than the U2414H although it shouldn't make much real difference. We were impressed by the high contrast ratio here on the U2415 which is about as good as you can hope for from an IPS-type panel at the moment. The factory calibration on both models offered a decent enough setup for most users, being slightly more accurate on the U2414H. Both models offered  good uniformity and no noticeable backlight bleed which was encouraging. Both featured the latest light AG coating and PWM-free backlights which was a positive step forward as well. Response times were as good as you can get from modern IPS-type panels as well, without introducing any significant overshoot, and input lag was very low on both models.

The all-round performance, features, specs and extras of both the U2414H and U2415 were impressive, so you can really choose based on whether you want a 16:10 aspect ratio screen or a 16:9 aspect ratio. The former is arguably a little better for office work and general desktop use, but the lack of a 16:9 scaling option means it is not really suited if you want to connect external devices for multimedia at all. The U2414H is a better option if you want to use external devices, or just prefer smaller/non-existent borders for your movies, films and games and those are more of a focus for you than general office work.

The U2415 made a very nice update to the U2412M as well. There's more modern connectivity options including HDMI offered, the new slim bezel design, USB 3.0 support, factory calibration and touch sensitive buttons on the new model. Dell have also moved to the light AG coating instead of the grainy old coating on the U2412M, and also used a flicker free backlight this time which is great news. Default setup is better on the U2415 thanks to the factory calibration, and Dell have also improved response times and eliminated the noticeable overshoot seen on the older model. All in all this is a better screen than the U2412M and if you're looking for a 16:10 aspect ratio 24" model this is a great all-round performer.

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