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Introduction

Out of their pretty extensive range it has been Dell's UltraSharp monitors which has always attracted the most attention over the years, with a great selection of sizes available, featuring high end panel technologies, specs and features. We've seen a lot of excitement when a new U-series screen arrived, most recently with the release of the 27" U2713HM and the news that we expect to see a refreshed 24" U2413 and 30" U3013 model some time early next year. The rest of Dell's extensive monitor line-up is normally reserved for lower cost models, with trimmed down feature sets and normally lower cost TN Film panels. However, recently Dell have released their new S-series range (the "S" stands for "studio" by the way), offering models of 21.5, 23, 24 and 27". Unlike their other lower cost models, these all feature higher end IPS (or AMVA in the case of the 24" model) panels and so are designed to be a mid-way solution, offering some higher end specs and technologies but while still maintaining a very low cost.

We will feature reviews of the other S-series models in the near future but for now we have the 24" S2440L with us for testing. This screen features an AMVA panel and offers a decent spec. Its connectivity and stand adjustment options are certainly more limited than the 24" UltraSharp models like the U2410 and U2412M, but it does come with a "frameless" edge-to-edge glossy glass front which some users have been shouting out for from more desktop monitors.

Dell's website says: "Dive into brilliance with the distinctive S2440L 24" monitor, featuring ultra-wide viewing, edge-to-edge glass and our Image Enhance feature. Images come alive with colour-boosting Image Enhance, ultra-wide viewing and Full HD resolution (1920 x 1080 max.) in a 16:9 widescreen format. Connect to a laptop or desktop with VGA connectivity. Explore a world of HD entertainment options with an HDMI port."

 


Specifications and Features

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

Monitor Specifications

Size

24"WS (60.97cm)

Panel Coating

Glossy Glass coating

Aspect Ratio

16:9

Interfaces

HDMI, VGA

Resolution

1920 x 1080

Pixel Pitch

0.277 mm

Design colour

Glossy black bezel and base, silver stand

Response Time

6ms G2G

Ergonomics

4 - 21 Tilt adjustment only

Static Contrast Ratio

5000:1

Dynamic Contrast Ratio

8 million:1

VESA Compatible

No

Brightness

250

Accessories

Power cord and block, D-sub cable, cable tie

Viewing Angles

178/178

Panel Technology

AMVA

Weight

With stand: 4.95Kg

Backlight Technology

W-LED

Physical Dimensions
 

WxHxD with stand
567.4 x 417.9 x 190.8 mm

Colour Depth

16.7m (8-bit)

Colour Gamut

Standard gamut, sRGB
~72% NTSC

Special Features

Audio out connection

Manufacturers website link: Dell

The feature set of the S2440L is certainly more limited than the popular UltraSharp models available. There are only 1x D-sub (VGA) and 1x HDMI connections available for video connectivity. There is no DVI and so you will need a DVI > HDMI cable or adapter if you want to connect from a DVI port on your graphics card. There is also no DisplayPort connection which is becoming increasingly popular nowadays. There is an audio out connection on the back of the screen if you want to listen to the sound sent over HDMI (if using HDMI end to end), but there are no integrated speaker on this model. While it is not listed in their specs, checking our graphics card control panel confirms the HDMI interface supports HDCP for encrypted content.

The screen comes packaged with only a D-sub VGA cable, and there is no HDMI cable provided since costs are being kept at a minimum here. The screen features an external power supply brick which comes packaged as well. There are no extra features here like USB ports or card readers, which are featured on some UltraSharp models from Dell.

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

Feature

Yes / No

Feature

Yes / No

Tilt adjust

DVI

Height adjust

HDMI

Swivel adjust

D-sub

Rotate adjust

DisplayPort

VESA compliant

Component

USB Ports

Composite

Card Reader

Audio connection

Ambient Light Sensor

HDCP Support

Touch Screen

Integrated Speakers

Hardware calibration

Uniformity correction



Design and Ergonomics


Above: front view of the screen. Click for larger version

The S2440L comes in a pretty much all-glossy design. The front of the screen and the base of the stand are both glossy. Black plastics are used for the edge bezel of the screen and for the squared base of the stand. The bezel does not protrude at the front of the screen and so the entire front is flat, giving the "frameless" design that quite a few manufacturers are starting to promote. There is of course a bezel along the sides of the panel and in the case of the S2440L this measures ~18mm along all edges.  With the edge-to-edge coverage, you can use these screens quite nicely for side by side multi-screen setups as shown below.

The monitors arm is a matte silver plastic. A shiny silver Dell logo is situated on the front of the screen in the middle of the lower bezel, but no other writing is present around the other edges. The OSD operational buttons are located on the bottom right hand edge with a subtle grey coloured power logo, and 4 small grey circles. These controls are touch-sensitive and we will look at this in more detail shortly.

The front of the screen is covered with a glossy edge-to-edge glass screen coating which produces a strong reflection. It makes the screen look quite attractive when set on the desk, but it is a very reflective screen surface, more so even than a normal glossy panel coating. It is also good as a protective, hard layer in front of the panel.

The glossy finish provides a very different feel to normal matte AG coatings. It can make colours and blacks "pop" and the image feels very different. However, it can often introduce distracting reflections when it is used, and it's no exception here on the S2440L. In fact I would say it is more reflective than many other glossy screens we have used and buyers should be wary of this if they have windows or lamps nearby which could become problematic. It is the glass coating which is accentuated this glossy feel here. It can also become a pain with finger prints and smudges, so keep a cleaning cloth handy!

The stand comes dismantled in the box but is easily clipped together. The arm slots into place on the base and is tightened as shown above using the small thumb screw. The arm then easily slots into the back of the monitor where a release button is also provided if you ever need to take the arm off. The screen is not however VESA compliant, and so is not mountable separately unfortunately.


Above: view of the base and rear of the display. Click for larger versions

The back of the screen has a rounded black matte plastic finish, with a Dell logo at the top as shown. The video connections are housed within a small inset section at the back. There is a small cable tidy clip provided to position the cables out of the way behind the arm of the screen. A further cable tie is provided in the box to help keep things neat if needed.


Above: side views showing profile and full tilt range. Click for larger versions

The screen has a nice thin profile from the side thanks to the use of W-LED backlighting and an external power brick. The stand provides only a basic tilt adjustment with a range of -4 to 21 provided. This is smooth and easy enough to manoeuvre thankfully and it offers a decent range. There is sadly no height, swivel or rotate adjustment available as Dell have opted for a more basic, and lower cost stand to keep retail costs of the S-series down. The screen is fairly wobbly when being moved but remains stable enough on the desk when it's not. The bottom edge of the screen is ~80mm above the height of the desk when vertical.

A summary of the screens ergonomic adjustments is shown below:

Function

Range

Smoothness

Ease of Use

Tilt

-4 to +21

Smooth

Easy

Height

n/a

 

 

Swivel

n/a

Rotate

n/a

Overall

Only tilt available but easy to use and smooth movements.



Above: schematics for the S2440L. Click for larger version

Materials were of a high quality and the build was good. There was no audible noise from the screen during use and it also remained nice and cool thanks to the W-LED backlight unit. A full screen dimensions and measurements diagram is provided above for reference as well.


Above: view of interface connections. Click for larger version

The back of the screen features the interface connections shown above. There are video connections for HDMI and D-sub, along with an audio output for if you are using the HDMI and sending audio to the screen as well. The connection on the far right of the above image is for the external power brick.

 



OSD Menu


Above: view of OSD operational buttons. Click for larger version

The S2440L features touch sensitive OSD control buttons which are located on the bottom right hand edge of the screen as shown above. These do not light up like they did on some older Dell models (e.g. U2410) but work nicely and are sensitive.

Pressing any of the 4 buttons brings up the quick launch menu, giving you quick access to preset mode selection and brightness / contrast controls. You can also select to enter into the main menu, or simply exit the quick launch menu. You can in fact personalise the two quick launch options from within the main menu should you wish to. Within the preset modes menu there are options for standard, multimedia, movie, game, text, warm, cool and custom colour.

Bringing up the main menu presents you with various sub-sections down the left hand side as shown. At the top right, like on other recent Dell screens, there is an "energy use" bar which gives you a visual indication of the power consumption at any given time. This is based on the OSD brightness setting which controls the backlight intensity, and therefore has a direct correlation to the power consumption. The brightness/contrast section is self explanatory of course. The second section for "auto adjust" is only relevant when using the analogue D-sub connection and is greyed out when using digital HDMI.

The input source section allows you to manually select which interface is in use. There is also a handy 'auto select' mode which will switch to whichever interface is active.

Colour settings allows you to change a couple of settings relating to colour format, but perhaps more useful here is access to the preset colour modes. There is also an 'image enhance' option here which serves to artificially exaggerate the sharpness of the image. This may be ok for movies and games perhaps but in normal use it doesn't look right.

The preset modes listed here are the same as those accessed via the quick launch menu.

 

The display settings section allows you to change the monitors aspect ratio for external devices and games. There are options for wide 16:9, 4:3 and 5:4 here. You can also turn the dynamic contrast ratio control on and off in this section of the menu, if you are in a suitable preset mode where it can be activated. We will look at this later on in the review.

The personalize section allows you to change the quick launch keys if you wish. You can change them to activate auto adjust, input selection and aspect ratio if you wish.

You can access the monitors factory menu as well but be careful not to change anything without knowing what you've done or how to change it back. Use the menu at your own risk! To access the factory menu, hold the top two buttons down while powering the monitor on. Once it is on, press the top button to bring up the menu. You can define the RGB levels for each of the colour temp preset modes here and there are a few other settings relating to the operation of the display.  There is no control for the overdrive (OD) impulse here which we have seen on some other Dell screens in the past so we will be reliant on the manufacturers set up.

Overall the OSD menu offers a decent range of options and it is intuitive and well structured. We are used to this menu as it has been used on Dell monitors for a while now.

 

Power Consumption

In terms of power consumption the manufacturers spec states typical usage of 18W. In standby the screen apparently uses <0.5W.

State and Brightness Setting

Manufacturer Spec (W)

Measured Power Usage (W)

Factory Default (75%)

18.0

18.2

Calibrated (45%)

-

15.3

Maximum Brightness (100%)

-

20.0

Minimum Brightness (0%)

-

9.4

Standby

<0.5

0.7

We tested this ourselves and found that out of the box the screen used 18.2W of power while at its default brightness setting which was 75%. At the lowest brightness setting, power consumption was reduced to 9.4W and at maximum 100% brightness it reached 20.0W. After calibration the brightness setting had been adjusted to 45% and the power consumption was measured at 15.3W. In standby the screen used 0.7W of power. We have plotted these measurements on the graph below for comparison with other screens:




Panel and Backlighting

Panel Manufacturer

AU Optronics

Colour Palette

16.7 million

Panel Technology

AMVA

Colour Depth

8-bit

Panel Module

M240HVN01 V0

Colour space

Standard gamut, ~sRGB

Backlighting Type

W-LED

Colour space coverage (%)

~72% NTSC

Panel and Colour Depth

The Dell S2440L utilises an AU Optronics AMVA M240HVN01 V0 panel which is capable of producing 16.7 million colours with a true 8-bit colour depth. The panel is confirmed when removing the back of the screen as shown below:


Above: dismantled screen. Click for larger versions
 

Panel Coating

The screen coating on the S2240L is a glossy solution. The panel surface itself is glossy which you can see if you dismantle the monitor as it has no protective coating applied to it. This is different to other AMVA panels we have seen in the past which normally feature a light AG coating. To the front of the screen an edge-to-edge glass layer is added which increases the overall glossy feel of the screen and provides protection for the panel. This is very reflective, more so than some other glossy coated screens we have seen before. Users need to be careful when selecting a screen like this as windows, lighting or lamps can become problematic depending on your working conditions. Smudges and finger prints may also prove troublesome.
 

Backlighting and Colour Gamut

The S2440L uses White-LED (W-LED) backlighting producing a colour space approximately equal to the sRGB reference. This means the screen is considered a 'standard gamut' backlight type. The gamut would cover approximately 72% of the NTSC reference space. A wide gamut screen would need to be considered by those wanting to work outside of the sRGB colour space of course.
 

PWM Flicker Tests at Various Backlight Brightness Settings

100%                                     50%                                       10%

Pulse Width Modulation Used

No

Cycling Frequency

n/a

Possible Flicker at

 

100% Brightness

No

50% Brightness

No

10% Brightness

No

We tested the screen to establish the methods used to control backlight dimming. Our recent article talks in more details about a common method used for this which is called Pulse Width Modulation (PWM). A series of photos was taken using the method outlined in the article. These were taken at 100%, 50% and 10% brightness settings. We would normally also test this at 0% brightness but the screen was so dark it was hard to get a decent photograph. These tests allow us to establish 1) whether PWM is being used to control the backlight, 2) the approximate frequency at which this operates, and 3) whether a flicker may be introduced or potentially noticeable at certain settings.

A thin white line was shown on an all-black background and a photograph was taken at a slow shutter speed of 1/8 second (in this example) as the camera was scanned left to right in front of the screen. This produces a series of white lines which can be used to identify the frequency of the PWM and how quickly the backlight is cycled on and off. The higher this 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. Please remember that not every user would notice a flicker from the backlight 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. We are able to at least measure the frequency of the backlight using this method and tell you whether the duty cycle is sufficiently short at certain settings that it may introduce a flicker to those sensitive to it.

Interestingly the Dell S2440L does not use PWM at all for dimming of the backlight. Even at 0% brightness there was no sign of the usual splitting of the white line that you'd expect to see in these tests. We carried out the checks at an even slower shutter speed which returned the same result. This is great news for those who are affected by flickering backlights and suffer from eye fatigue and eye strain. It seems we have seen quite a few new monitors recently which don't use PWM for backlight dimming. The HP ZR2740w, DGM IPS-2701WPH, ViewSonic VP2770-LED, Samsung S27B970D and Dell U2713HM spring to mind as other models which do not use PWM which we have tested recently.
 

Note 14/11/12 - We have had a few users contact us in relation to their S2440L units with information suggesting that they are perhaps using PWM for backlight dimming. These users have been based elsewhere in Europe (Sweden and Germany) but it seems there may be some units of this screen which do in fact use PWM. Other users, including review site pcmonitors.info have confirmed units without PWM. It seems that perhaps there are different versions of this screen out there, and perhaps even some panel swapping going on? I would like to make the point that PWM dimming does not cause issues for most people, but I am including the note here for completeness and while we try to gather additional information about the screen and panels. If you are affected by PWM related issues, you may want to be cautious about this screen at this stage.

If any owners of the S2440L can get in touch with us to confirm their units that would be welcomed. Please try and run the PWM tests described in our article and take photos to test at various backlight levels. If any users can also remove the back from their screen to confirm the panel part being used, that would be very useful.


 


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.

I restored my 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 new i1 Display Pro colorimeter) combined with LaCie's Blue Eye Pro software suite. An NEC branded and customised X-rite i1 Display 2 colorimeter was also used to verify the black point and contrast ratio since the i1 Pro 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

IMPORTANT NOTE: Before we get into this section we need to make an important note about use of the HDMI port. The screen only features a single D-sub VGA and 2x HDMI port. Naturally you will probably want to use the digital HDMI connection if you can for optimum picture quality. If you have an NVIDIA graphics card and want to use the HDMI at all, whether a straight HDMI > HDMI connection or a DVI > HDMI conversion, you need to make a change to your graphics card settings to display the optimum picture. This is because by default the output range over HDMI is limited by the graphics card, and it can greatly limit the picture quality and in particular the black range and contrast ratio.

When connected via HDMI on an NVIDIA graphics card the screen by default will not look right, and the black range in particular is poor. In fact we obtained static contrast ratios of only ~400:1 in the default mode before making this change and originally thought the screen was at fault. A change is needed via your graphics card to ensure a full 0 - 255 output when using HDMI, rather than it being limited to a smaller output range of 16 - 235. This applies to NVIDIA cards but is only necessary when connecting to the HDMI port on the screen and is not needed when using D-sub. A similar change might be required when using an AMD graphics card but the setting is built into their graphics card drivers we believe. For NVIDIA cards the simplest way to ensure a full output range is to use the handy toggle utility available here. If you run the program you can select a full 0- 255 range quickly and easily.

 

Anyway, default settings of the screen were as follows:

Monitor OSD Option

Default Settings

Brightness

75

Contrast

75

Picture mode

Standard

RGB

n/a


Dell S2440L - Default Factory Settings

  
  

 

Default Settings

luminance (cd/m2)

186.02

Black Point (cd/m2)

0.06

Contrast Ratio

3012:1

 

The default set of the screen felt ok to the naked eye, perhaps a little cool, and as is normal for most screens it was too bright for comfortable use. Colours appeared to 'pop' somewhat because of the glossy screen coating and it felt different to models using AG coating. In terms of measurements, the CIE diagram on the left confirms that the monitors colour gamut (black triangle) matches the sRGB colour space (orange triangle) reasonably closely. It extends a little past the sRGB space in some shades, particularly in blues, but falls a little short in some others in greens in this 2D view of gamut. There is no sRGB emulation mode on this model and so you cannot more closely match the sRGB space than the native gamut of the backlight.

 

 

Default gamma was measured at 2.3 average, leaving it 4% out from the target of 2.2. This was too high in darker shades, but a bit closer to the 2.2 figure in lighter grey shades, as shown in the more detailed table above. The white point was measured at 7003k, being 8% out from the target of 6500k which wasn't too bad, but a bit cool. Colour accuracy was very good with an average dE of 1.8 and maximum of 4.8. Colour gradients showed smooth transitions in lighter shades, but at the darker end there was some gradation and some banding evident. Luminance was too high as we had suspected, being measured at 186 cd/m2 by default while at the 75% brightness setting. We achieved a very high static contrast ratio of 3012:1 by default which was about what we'd expected from a modern AMVA panel. These panels aren't quite living up to their 5000:1 spec yet but this is still far more than any TN Film, IPS or PLS panel can offer. Once again, you do need to change the colour format if you're using HDMI on an NVIDIA card, otherwise contrast ratio will suffer massively.

 

 

 

Calibration Results

 

I wanted to calibrate and profile the screen to determine what was possible with optimum settings and profiling. I used the X-rite i1 Pro spectrophotometer combined with the LaCie Blue Eye Pro software package to achieve these results and reports. An NEC branded and customised X-rite i1 Display 2 was used to validate the black depth and contrast ratios due to lower end limitations of the i1 Pro device.


Dell S2440L - Calibrated Settings

Monitor OSD Option

Calibrated Settings

Brightness

45

Contrast

75

RGB Channels

99, 92, 92

Preset Mode

Custom Color

   

 

Calibrated Settings

luminance (cd/m2)

121

Black Point (cd/m2)

0.04

Contrast Ratio

2954:1

 

I reverted to the 'custom color' mode in the preset section of the OSD menu which would allow me access to the individual RGB channels. Adjustments were also made during the process to the brightness control, and to the RGB channels as shown in the table above. This allowed me to obtain an optimum hardware starting point and setup before software level changes would be made at the graphics card level which would help preserve tonal values. After this I let the software carry out the LUT adjustments and create an ICC profile. The screen does not feature a hardware LUT calibration option so other than the OSD alterations, the rest of the process is carried out at a graphics card level in profiling the screen.

 

Average gamma had been corrected to 2.2 with 0% deviance according to the initial test correcting the default 4% deviance we'd found in this preset. The 8% deviance in the white point from our target of 6500k had also been corrected here and the colour temperature was now pretty much spot on at 6479k. Luminance had also been corrected thanks to the adjustment to the brightness control, now being measured at 121 cd/m2. This also gave us a calibrated black depth of 0.04 cd/m2, and an excellent calibrated static contrast ratio of 2954:1. Colour accuracy had also been corrected nicely, with dE average of 0.6 and maximum of 1.3. LaCie would consider colour fidelity to be excellent now overall.

 

Testing the screen with various colour gradients showed mostly very smooth transitions. There was some slight gradation in darker tones and some very slight banding evident as we'd seen at default settings. Nothing too major though that would be noticeable to most normal users. Unlike most other panels in the market, this screen does not feature anti-glare (AG) coating. Instead it uses a glossy screen coating and as a result the colours look clean and crisp, the image quality is sharp and whites in particular look a lot more pure than they do on heavy AG coated screens like some of the IPS alternatives available. Glossy coating isn't to everyone's taste though as it can introduce reflections which are annoying, particularly so on this glass fronted model. You should probably try and see a glossy and an AG coated panel in person if you are unsure what to buy.

 

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

 

 

 

We've extended the comparisons made in this section to try and 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 S2440L was pretty good when it comes to gamma and white point. There was a small 4% deviance in gamma and a slightly higher 8% deviance in white point. This represented a pretty good factory setup, much like we'd seen from the Dell U2212HM, U2312HM and U2412M. Colour accuracy was also very good with dE average of 1.8, again close to what we'd seen from the U2212HM and U2312HM, and a little better in fact than the U2412M.
 

 

 

Default colour accuracy is compared again on the above graph, with the S2440L having a very reliable default setup which is pleasing, especially given the low cost of this model.

 

Once calibrated the dE average was reduced to 0.4. This would be classified as excellent colour fidelity by LaCie. It was not quite as low as some of the other screens here which reached down to 0.2 average, but in practice you would not notice any difference here at all. The professional range models from NEC and Eizo are even more accurate than other models shown here. Professional grade monitors like those offer other high end features which separate them from some of these other models, including extended internal processing, 3D LUT's and hardware calibration. These comparisons are based on a small selection of tests, so it should be remembered that other factors do come into play when you start talking about professional use.

 



 

The calibrated black depth and contrast ratio of the S2440L were excellent, with a static contrast ratio on par with the other AMVA panels we've tested at 2954:1. This is much higher than we have seen from any IPS, TN Film or PLS panel and is certainly a strong point of AMVA technology.

 

 

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Contrast Stability and Brightness

I wanted to see how much variance there was in the screens contrast as we adjusted the monitor setting for brightness. In theory, brightness and contrast are two independent parameters, and good contrast is a requirement regardless of the brightness adjustment. Unfortunately, such is not always the case in practice. We recorded the screens luminance and black depth at various OSD brightness settings, and calculated the contrast ratio from there. Graphics card settings were left at default with no ICC profile or calibration active. Tests were made using an NEC branded and customised X-rite i1 Display 2 colorimeter. It should be noted that we used the BasICColor calibration software here to record these, and so luminance at default settings may vary a little from the LaCie Blue Eye Pro report.

OSD Brightness

Luminance
(cd/m2)

Black Point (cd/m2)

Contrast Ratio
( x:1)

100

192.96

0.06

3216

90

188.00

0.06

3133

80

182.20

0.06

3037

70

169.32

0.05

3386

60

150.51

0.05

3010

50

130.73

0.04

3268

40

110.85

0.04

2771

30

91.44

0.03

3048

20

71.16

0.02

3558

10

50.36

<0.02

-

0

30.01

<0.02

-

 

Total Luminance Adjustment Range = 162.95  cd/m2

Total Black Point Adjustment Range = > 0.04 cd/m2

Average Contrast Ratio = 3159:1
Recommended OSD setting for 120 cd/m2 = 44%

The luminance range of the screen was good. At the top end the panel reached 192.96 cd/m2 which was actually a fair bit short of the specified maximum of 250 cd/m2, but probably fine for most users as an upper limit. At the lower adjustment end it could reach down to a very low 30.01 cd/m2 meaning the screen should be perfectly fine even in darkened room conditions, and for those who like to run at a lower luminance setting. A brightness setting of ~44% should return you a default luminance of around 120 cd/m2 as well. Black point remained very low across the adjustment range, from 0.06 cd/m2 down to below 0.02 cd/m2, the lower limit of the X-rite i1 Display 2 device.

We have plotted the luminance trend on the graph above. The screen behaves as it should, with a reduction in the backlight intensity controlled by the reduction in the OSD brightness setting. This was not a linear relationship overall as the adjustment range from 100 to 80% showed a smaller actual change in the overall luminance than each additional step. The change was steeper from 80% downwards as you can see from the graph above.

We will not provide our usual contrast stability graph since the low black levels mean that the rounding errors are too high and it would not fairly represent the stability of the contrast. Average contrast ratio measured was ~3159:1 which was excellent.

 


Dynamic Contrast

The Dell S2440L features a dynamic contrast ratio (DCR) control, which boasts a spec of 8,000,000:1 (8 million:1). Dynamic contrast ratio involves controlling the backlight of the screen automatically, depending on the content shown on the screen. In bright images, the backlight is increased, and in darker images, it is decreased. We have come to learn that DCR figures are greatly exaggerated and what is useable in reality is often very different to what is written on paper or on a manufacturers website.

For this test I would use the colorimeter to record the luminance and black depths at the two extremes. Max brightness would be recorded on an almost all white screen. Black depth would be recorded on an almost all black screen. In real use you are very unlikely to ever see a full black or full white screen, and even our tests are an extreme case to be honest. Carrying out the tests in this way does give you a good indication of the screens dynamic contrast ratio in real life situations however.

The DCR feature is available in only the movie and game preset modes, and for some reason not in the multimedia preset. It has a simple setting for on or off and once enabled you cannot control the brightness setting manually. If you do try to change it you are given the above warning and the option to turn the DCR feature off.

 

Dynamic Contrast

Specified DCR Range

8 million: 1

Available in Presets

movie, game

Settings

On / Off

Max luminance (cd/m2)

187.20

Min Black Point (cd/m2)

0.06

Max Dynamic Contrast Ratio

3120:1

We tested the DCR feature and you could immediately notice the screen getting much brighter when you first turn it on compared with the standard preset. You can observe the changes being made in the OSD by looking at the energy meter in the top right hand corner. Switching to this mode in normal office-type applications showed the energy bar fill up to maximum, indicating that the brightness was being turned up to a high setting. When switching between an almost all-white and an almost all-black screen there was no change at all to the luminance of the screen, detectable either to the naked eye or by looking at the energy meter. As a result, we didn't obtain a contrast ratio any higher than we'd seen from our static contrast ratio tests before.

We tested the screen with a completely black screen as well and you could tell from the OSD energy meter that it was then able to control the backlight a bit, down to around the 50% setting by the look of things. This would in theory give you a better DCR of around 4800:1 but it should be noted that it would be extremely rare to ever see a 100% black image in real use and so this is more of a theoretical DCR than a realistic, practical DCR. You'd have to be turning the backlight completely off on an all-black image to achieve anything higher really here and anything near the crazy spec being quoted. Some screens do actually do that which allows for exaggerated laboratory testing and their resulting specs, but in the case of the S2440L it was not turning the backlight off. In normal use, the DCR is pretty much useless.

 


Viewing Angles


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

Viewing angles of the S2440L were characteristic of an AMVA panel. Horizontally they were reasonably wide although there was a contrast shift from an angle of >40 either side which made the image go pale and yellow quite noticeably. From a wider angle still the image had a more pronounced pale tinge to it and you can pick this out from the images above. Vertically they were a bit more restrictive still with a fairly noticeable contrast shift detectable with even a slight movement up or down, and a pale tinge to the image being more obvious. This was also a little yellow from a wider angle, and this is brought out in the photos above. The viewing angles were certainly better than TN Film matrices in these regards, and free of the obvious vertical darkening you see from TN Film technology. However, they were not as wide as IPS or PLS matrices and the contrast shifts were more noticeable unfortunately.

There was also a pretty obvious off-centre contrast shift which is inherent to VA panel types. Using a test image which shows a dark grey font on a black background you can easily test this 'feature'. From head on, the text was invisible and largely lost within the black background. This is down to the pixel alignment in a VA matrix. As you move away from a central line of sight the text becomes lighter and is more easily visible, especially from an angle of about 45. This is an extreme case of course as this is a very dark grey tone we are testing with. Lighter greys and other colours will appear a little darker from head on than they will from a side angle, but you may well find you lose some detail as a result. This can be particularly problematic in dark images and where grey tone is important. It is this issue that has led to many graphics professionals and colour enthusiasts choosing IPS panels instead, and the manufacturers have been quick to incorporate this alternative panel technology in their screens. I would like to make a point that for many people this won't be an issue at all, and many may not even notice it. Remember, many people are perfectly happy with their TN Film panels and other VA based screens. Just something to be wary of if you are affected by this issue or are doing colour critical work.


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

On a black image there is a slight pale and purple/blue tint introduced to the image when viewed from a wide angle. This isn't too severe and shouldn't present any real problems in practice.



Panel Uniformity

Measurements of the screens luminance were taken at 35 points across the panel on a pure white background. The measurements were taken using BasICColor's calibration software package, combined with the NEC customised X-rite i1 Display 2 colorimeter. The above uniformity diagram shows the difference, as a percentage, between the luminance recorded at each point on the screen, as compared with the reference point of a calibrated 120 cd/m2. This is the desired level of luminance for an LCD screen in normal lighting conditions, and  the below shows the variance in the luminance across the screen compared with this 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 overall uniformity was good here. There was a slight drop in luminance down to 104 cd/m2 along the left hand edge but overall around 83% of the screen was within 10% deviance of the central 120 cd/m2 measurement. A decent performance here really given the low cost of the screen.


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. There was no major backlight leakage although there was some slight clouding in the bottom right hand corner which the camera picked up in the photo above. This shouldn't present any real problem in practice though and it was quite minimal. Again a good performance here from the S2440L. We should note that we actually had chance to test two random stock samples of this screen and found both to return similar results as above in terms of backlight leakage.



General and Office Applications

The S2440L offers a variable performance when it comes to office work. Firstly the 1920 x 1080 resolution and 24" screen size give a nice decent area in which to work although the vertical resolution is a little less than 16:10 aspect 24" models (1920 x 1200). I think you notice this if you come from a 16:10 format screen. Also 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 1080 resolution should be adequate for many users. The screen offered a comfortable 0.277mm pixel pitch which delivered easy to read text at a nice size, in my opinion. The resolution is certainly big enough for side by side split screen working as well in many cases.

 

One area which raises questions here though is the glossy screen coating and glass front. While the screen might look attractive sat on the desk, it can become a little tricky to use in certain conditions. The glossy coating does help with the 'feel' of the images and colours and blacks can 'pop' when it is used by display manufacturers. However, reflections become quite a problem, and on the S2440L the glossy-ness seemed to be quite severe. You need to be very careful about the position of your screen with your surrounding light sources, otherwise reflections become a pain. This might not be a problem for many users, and it's the same issue you'd face with any glossy screen really. For office work personally I found it a bit difficult.

 

Default luminance of the screen is a little too high at around 186 cd/m2 at the default 75% brightness setting. You will probably want to turn this down to around 44% for a comfortable luminance around 120 cd/m2. Those wanting to use the screen in low lighting conditions shouldn't have any issue here as the brightness control offers an excellent adjustment range, down to ~30 cd/m2 in fact. The default colour, white point and gamma setup are very good thankfully so even without a colorimeter device you should be able to achieve decent performance from the screen easily. Another thing to note while we are talking about the brightness control is that the screen does not use Pulse-Width modulation (PWM) to control backlight dimming and so those who suffer from eye fatigue or headaches associated with flickering backlights need not worry here. (Note 14/11/12 see our panel section for an update on this)

 

There is a specific preset mode for 'text' in the OSD menu which accentuates the sharpness of the image. This seems to enable the 'image enhance' feature (which is then greyed out) which in my opinion makes the text and image look too sharp and a bit unrealistic. The normal standard or custom color preset modes would be better, with image enhance left off. The default sharpness setting of 50 in the OSD also seemed optimal.

 

I tested the screen with both HDMI and D-sub interfaces, and the HDMI digital signal was a little sharper than VGA. You will want to use HDMI for the sharpest text and image where possible (making sure to adjust your graphics card settings if using an NVIDIA card and HDMI). There are no USB ports featured on this model since Dell have trimmed down the features to keep costs low. Those can be pretty handy for connecting external devices, so it's a bit of a shame to see them gone. The stand is also very basic, offering only a tilt adjustment. While this is easy to use, the height, swivel and even rotate adjustments are missed I think for office uses and the screen is perhaps a little too low as a result.

 
Above: photo of text at 1920 x 1080 (top) and 1600 x 900 (bottom)

The screen is designed to run at its native resolution of 1920 x 1080 and at 60Hz refresh rate. If you want to you can run it outside of this and let the image be scaled to fill the screen. At the native resolution text was sharp and clear. We ran the screen at 1600 x 900 which was the next step down, while still maintaining the screens 16:9 aspect ratio. Text was more blurred and you do take a hit in terms of resolution of course. To give you more desktop real estate and maximum picture quality, the native resolution is of course recommended where possible.

 


Responsiveness and Gaming

The S2440L is rated by Dell as having a 6ms G2G response time which implies the use of overdrive / response time compensation (RTC) technology. This is used to boost pixel transitions across grey to grey changes and improve responsiveness in practice, and reduce ghosting and blurring. The panel being used is an AU Optronics AMVA M240HVN01 V0 Panel. We have seen mixed performance in the past from AMVA panels, with older versions being inherently very slow and showing quite noticeable blurring and ghosting in these tests. Some recent AMVA panels have made improvements, so let's hope for the same here from the S2440L. It should be noted that unlike some other Dell screens, you cannot turn the overdrive control on and off from within the factory OSD and so we are reliant on Dell's setup here.

Display Comparisons

The screen was 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.



24" 6ms G2G AU Optronics AMVA

In practice the Dell S2440L showed pretty low levels of motion blur and it was free from the obvious ghosting and blurring you can see from some older AMVA panels. Movement was pretty smooth and the image looked sharp. There was a fairly noticeable dark trail introduced however which is caused by an overshoot of the overdrive impulse. This overdrive is being applied too aggressively and is causing the pixels to overshoot their desired orientation, producing a dark trail in these tests. This is noticeable to the naked eye although not too severe.
 


24" 6ms G2G AU Optronics AMVA


24" 8ms G2G LG.Display e-IPS


23" 8ms G2G LG.Display e-IPS


24" 6ms G2G LG.Display H-IPS

I have provided first of all a comparison of the S2440L against 3 other Dell screens. We had seen some similar dark trailing on the Dell U2412M as well which you can see from the above images. It is perhaps a little more obvious on the S2440L but both models seem to suffer from a poorly controlled overdrive impulse. It was a similar story with the 23" U2312HM as well. You can eliminate that on the U2412M and U2312HM by turning the overdrive control off in the factory OSD, but at the cost of overall responsiveness. The older 24" Dell U2410 showed good response times with low levels of blur (not quite as low as the U2412M), and also freedom from these dark overshoot artefacts.


24" 6ms G2G AU Optronics AMVA


24" 8ms G2G AU Optronics AMVA (AMA setting = On)


24" 4ms G2G AU Optronics AMVA (AMA = Premium)
 

If we compare the S2440L with two other 24" AMVA panels we have tested, the differences become more obvious. The BenQ EW2420 was the first AMVA + W-LED on the market and its older generation AMVA panel was very slow. There is obvious blurring and ghosting in practice and it wasn't suitable for gaming as a result. Big improvements were made by the time we tested the BenQ GW2450HM more recently, with responsiveness finally reaching the kind of levels you'd see from competing IPS panels. Blurring was greatly reduced although there was some slight dark overshoot here. The Dell S2440L performs quite similarly to the GW2450HM in terms of blur, but the dark overshoot is more pronounced.



24" 6ms G2G AU Optronics AMVA


24" 2ms G2G AU Optronics TN Film + 120Hz (AMA = On)


27" 1ms G2G Chi Mei Innolux TN Film + 120Hz (Over Drive = 0)


22" 3ms G2G Samsung TN Film + 120Hz

We've also included a comparison above against three very fast 120Hz compatible screens we have tested. In all cases these other screens are using TN Film panels and are aimed primarily at gamers. Firstly there is a comparison against the BenQ XL2420T. This showed very low levels of motion blur, but some dark overshoot was introduced as a side-effect. The Iiyama G2773HS was very responsive and even has a quoted 1ms G2G response time. This showed very low levels of blur and had minimal issue with overshoot. The Samsung SM2233RZ performed very well in these tests and showed very low levels of motion blur also. When 120Hz mode was enabled the overdrive artefacts evident in 60Hz mode were almost completely eliminated, which is something we have seen with the BenQ XL2420T as well.

While these pixel response tests show the S2440L to have pretty fast transitions and low levels of motion blur (albeit with some overshoot), there is something else going on as well here which can't be picked out by the camera. All of these other TN Film models are running at 120Hz refresh rates, which allows for improved 120fps frame rates and 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. From a pixel response point of view the S2440L performed very well, but there are some other areas you still need to think about when it comes to high end gaming. It couldn't keep up with the very fast TN Film models with 120Hz support.
 

The responsiveness of the S2440L was pretty good overall. Thankfully although it was based on an AMVA panel it performed much better than older generation panels, and up to the standards we'd seen from a couple of recent models. The blurring was at a low level but unfortunately Dell's overdrive controlled seemed to be a little variable. A dark overshoot artefact was fairly pronounced, a little more than the recent U2412M and U2312HM in fact which had suffered in the same way. Overall it should still be fine for most normal users.

 

Additional Gaming Features


Aspect Ratio Control - The screen offers three options within the OSD menu for hardware level aspect ratio control. There are options to maintain the aspect ratio at 16:9, 4:3 or 5:4 ratios which should be adequate for most users and for the connection of most external devices. It would have perhaps been useful to see an "auto" mode, capable of detecting and maintaining the source aspect ratio automatically, and perhaps a 1:1 pixel mapping mode for those who didn't want the source image stretched at all. Each of the modes provided would stretch the source image to fill as much of the screen as possible, but will maintain the selected aspect ratio. In addition even if the input source is not one of the specific aspects listed, it will be forced to that aspect if you select it. For instance if you input the native 1920 x 1080 resolution, but select 4:3 aspect, it will squash the screen sideways to meet a 4:3 aspect, but the image will just be squashed accordingly. It can be a little annoying having to manually change the aspect ratio each time if you input different aspect sources.

Preset Modes - There is a 'game' preset mode available from within the preset mode menu. This seems to be a little warmer than the standard preset mode. We've already established that the DCR doesn't offer anything in real use sadly. The game preset mode also seems to accentuate the sharpness setting. This mode might be useful if you want to set up a specific mode to be different to your day to day normal use profile as well.

 


Input Lag

We have recently written an in depth article about input lag and the various measurement techniques which are used to evaluate this aspect of a display. We have also improved our method by adopting the SMTT 2 (now version 2.5.1) tool which is used to generate the results below. Please see our full input lag testing article for all the details.

Input 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.

 Class 1

Our tests here are based on the new format using SMTT 2.0. We have provided a comparison above against other models we have tested to give an indication between screens. We have only included screens which were tested using this new method to allow for a fair and realistic comparison, and have removed any models tested using the old method.

The Dell S2440L shows a very low level of input lag. This was measured at 5ms average. Note that this is the overall display lag, and so accounts for the signal processing time + an element of the pixel response time. The lag of this screen has been categorised as CLASS 1 as detailed above. It should be perfectly fine for gaming as a result, even for fast paced FPS.

For more information about the SMTT 2.0 tool, or to purchase a copy please visit:

http://smtt.thomasthiemann.com/index_en.html

 


Movies and Video

 The following summarises the screens performance in video applications:

  • 24" screen size makes it a pretty small option by today's standards for an all-in-one multimedia screen, being quite a bit smaller than modern LCD TV's and many other desktop monitors now available.

  • 16:9 aspect ratio is more well suited to videos than a 16:10 format screen, leaving smaller borders on DVD's and wide screen content.

  • 1920 x 1080 resolution can support full 1080 HD resolution content

  • Digital HDMI interface supports HDCP for any encrypted and protected content

  • There is no additional DVI port available, only 1x HDMI and 1x VGA. While it's useful to have HDMI for connecting external devices, you would then be limited to using VGA for your PC. An extra DVI port or a second HDMI would have been useful here.

  • Glossy AG coating and glass front may cause issues with reflections depending on ambient lighting conditions. This could prove annoying in darkened rooms depending on the position of your light sources.

  • Wide brightness range adjustment possible from the display, including reasonable maximum luminance of ~193 cd/m2 and very good minimum luminance of ~30 cd/m2. Should afford you very good control for different lighting conditions.

  • Black depth and contrast ratio are excellent from the AMVA panel. Shadow detail in darker scenes should not be lost.

  • Dynamic contrast ratio doesn't really work at all on this model, in case there's those who like the feature.

  • 'Movie' preset mode available which exaggerates the sharpness and colours, making them look more vivid. Might be preferable to some users compared with a normal PC setup mode.

  • Good pixel responsiveness which should be able to handle fast moving scenes in movies without issue. Perhaps some issues apparent with overshoot in certain transitions.

  • Good hardware level aspect ratio control options which may be useful for connection of external devices, DVD players etc. Options for 16:9, 4:3 and 5:4 should satisfy most uses. A 1:1 pixel mapping mode or an "auto" aspect ratio retention might have been useful.

  • Wide viewing angles thanks to AMVA panel technology meaning several people could view the screen at once comfortable and from a whole host of different angles. The off-centre contrast shift inherent to VA panels may prove a problem in darker scenes where shadow detail could be lost depending on your line of sight. You may find yourself moving your head to see some of the detail in darker content if you are facing the screen head on.

  • Limited range of ergonomic adjustments available from the stand with only tilt available. Might be difficult to obtain a comfortable position for multiple users or if you want to sit further away from the screen for movie viewing.

  • No significantly noticeable backlight leakage, and none from the edges which is good. This type of leakage may prove an issue when watching movies where black borders are present but it is not a problem here.

  • No integrated stereo speakers on this model but an audio output is provided to take sound from the HDMI if it's being used.

  • Make sure you adjust your graphics card settings if using HDMI from an NVIDIA card to get the full range and proper contrast ratio.

  • Picture in picture (PiP) or Picture By Picture (PbP) is not available on this model.

  • For PAL sources, we have tested the screen and confirmed it will support the full native resolution of 1920 x 1080 at 50Hz refresh rate.

 

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Conclusion

The Dell S2440L is an interesting addition to the Dell monitor range. It's nice to see Dell try to fill a middle ground between their low cost office TN Film monitors and their more expensive high-end UltraSharp models and offer something a little different. These new S-line models come with a new design and many users will like the glossy plastics and the glossy glass screen coating. They certainly look nice on your desk, although we would certainly advise caution given the reflective nature of the glass front. The screen also offers a pretty reasonable spec and the use of an AMVA panel is an interesting change for Dell from their 24" IPS models they have on offer.

From a performance point of view, default factory setup was very good and should provide a decent performance for normal users without access to calibration tools. Black depth and contrast ratio were excellent as well which you would expect from a modern AMVA panel, and something which IPS technology cannot compete with at the moment. It was good to see PWM was not being used for backlight dimming as well on our sample, a positive trend we hope to see more of in the market. Pixel response times were also good and thankfully it offers faster performance than older generation AMVA models. With a very low input lag, this could handle gaming pretty well too. You do of course have to live with the AMVA viewing angles which can be a bit restrictive.

Obviously Dell have cut back a few things to try and offer a very low price. The screen retails for ~198 GBP (inc VAT) which makes it a little cheaper than the Dell U2412M (220) and U2410 (360). It has a far more basic stand with only tilt being available, so you need to think about whether you need more or not. There are also more limited connections with the screen missing DVI and USB which could have been handy. Having said that, the touch sensitive buttons add a bit of a premium feel, and the overall glossy edge-to-edge design helps avoid it feeling cheap at all which is great news. From the two samples we tested we were pleased with the build quality and lack of backlight bleed as well which is hopefully a good sign of the quality of these screens. The S2440L offers a decent alternative in the AMVA screen offerings and the glossy coating is bound to attract some buyers.
 

Pros

Cons

Excellent black depth and contrast ratio from AMVA panel

May be too glossy and reflective for some users

Very good default factory setup

Limited ergonomic adjustments, only tilt available

PWM not used for backlight dimming
(14/11/12 - see panel section for update)

Limited connectivity options

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