Tablet Displays Under Bright Ambient Lighting Shoot-Out

Apple iPad 2  –  Amazon Kindle Fire  –  Motorola Xoom  –  Samsung Galaxy Tab 10.1

 

Dr. Raymond M. Soneira

President, DisplayMate Technologies Corporation

 

Copyright © 1990-2012 by DisplayMate Technologies Corporation. All Rights Reserved.

This article, or any part thereof, may not be copied, reproduced, mirrored, distributed or incorporated

into any other work without the prior written permission of DisplayMate Technologies Corporation

 

 

Introduction

Tablets and Smartphones are all used under a very wide range of ambient lighting conditions that are frequently much brighter than for other displays – like laptops, desktops, and HDTVs. The screens reflect a considerable amount of the surrounding light, which washes out the images you are trying to see. The differences in display brightness and reflectance between models results in large differences in their screen readability, visibility and picture quality, especially under brighter ambient lighting. We demonstrate those differences visually by photographing them inside a laboratory Integrating Hemisphere using a powerful light source under a wide range of lighting levels.

 

Other than jacking up the screen Brightness, manufacturers have done very little to improve screen readability and picture quality under high ambient lighting. In fact, the displays on virtually all Tablets and Smartphones are mirrors that are good enough to use for personal grooming even in ordinary indoor ambient lighting. There are many anti-reflection coatings and treatments that can be used to significantly improve this situation together with color and intensity scale management profiles derived from the ambient light sensor. The second big payoff is that the display can then be viewed with a lower Brightness setting, which improves the running time on battery – something all users care about that provides a significant competitive edge.

 

There is very little information (other than anecdotal) on how Tablet and Smartphone displays perform and degrade under bright ambient lighting. Our Mobile Display Technology Shoot-Out article series measures the percentage of light reflected by each of the tested mobile screens, and our Auto Brightness Display Shoot-Out examines the optimum screen brightness levels needed under varying ambient light levels. In this article we photographically compare the displays on the Apple iPad 2, Amazon Kindle Fire, Motorola Xoom, and Samsung Galaxy Tab 10.1 at 8 ambient light levels from absolute darkness (0 lux) up through almost direct sunlight (40,000 lux). An accompanying article performs the same comparison on 4 Smartphones.

 

 

Results Highlights

When viewed and photographed in absolute darkness (0 lux) the Tablets and Smartphones all appear fairly similar, with differences in color saturation as the standout feature. But as the Ambient Lighting gets brighter the light reflected from the screens rises and begins washing out the display’s native colors and image intensities, eventually dominating and then overwhelming the entire image on screen as seen in the Screen Photograph sections below and in the accompanying article on Smartphones. As that happens the differences between the Tablet and Smartphone displays become quite noticeable and substantial.

 

The Screens:

The cover glass and additional layers (such as the touch screen and optional screen protector if you use one) that lie over the display panel currently don’t get as much attention or respect as they deserve for their considerable impact on picture quality and screen visibility in bright lighting. People primarily think about their impact on scratch resistance, breakage, and fingerprints. The reason they are so important to the image quality is that any external light that is reflected from the screen travels through the top layers twice: once on the way in and then again on the way out after being reflected. So if the layers affect the image characteristics by “x” then the reflected component is affected by x² (not 2x), which is considerably larger. So any problems or irregularities in the screens are magnified in bright ambient lighting. Consumers should use care in selecting a screen protector, because many increase the screen reflectance considerably, even those that claim to reduce it.

 

The Best:  Apple iPhone 4 and iPad 2 and the Samsung Galaxy S and Tab 10.1

With DisplayMate Contrast Ratings for High Ambient Light of 47 or more the Apple and Samsung displays deliver the best screen visibility and picture quality in bright environments as seen in the Screen Photographs sections below and in the accompanying article on Smartphones. In bright lighting the Apple and Samsung screens are fairly color neutral and do not impart any noticeable color caste, and there were no noticeable image irregularities introduced by the upper screen layers. While the Apple and Samsung models are decidedly the best, both the Lab Contrast Rating measurements and the Screen Photographs show that the Samsung Galaxy models are somewhat better – so Samsung is the declared winner for High Ambient Light performance, but only by a nose…

 

The Worst:  Amazon Kindle Fire, HTC Desire, and the Motorola Xoom and Droid X

With DisplayMate Contrast Ratings for High Ambient Light in the teens, 20s and low 30s the Amazon, HTC, and Motorola displays delivered much worse screen visibility and picture quality in bright environments as seen in the Screen Photographs sections below and in the accompanying article on Smartphones. The HTC Desire came in decidedly last place with by far the poorest performance. In bright lighting the Kindle Fire has a noticeable diagonal crosshatch pattern from the touch screen conductors, and the Droid X has noticeable diagonal banding introduced by variations in bonding the top layers. There is also a noticeable color caste introduced by the upper layers of the screens: the Kindle Fire has a green caste, the Xoom a blue caste, and the Desire and Droid X a cyan caste.

 

The Future:

With the rapid growth of Tablets, Smartphones and other mobile devices, the display performance under high ambient lighting will be increasingly important to consumers – not only for screen visibility, readability, and picture quality, but also for improving the display’s brightness power efficiency, which has a considerable impact on the running time on battery. All of these are important factors in producing competitive mobile devices. While Apple and Samsung are currently the best performers in high ambient light, it is possible to do substantially better with advanced scientific lab tests and analysis. Interested manufacturers should Contact DisplayMate Technologies for advanced specular reflectance and diffuse reflectance spectral analysis of displays, cover glass, optical layers, and screen protectors.

 

Master Photo Grid Summary:

The Master Photo Grid has all of the Screen Shots for the Tablets and Smartphones under Ambient Lighting in a compact format. When viewing on displays with at least 1920 pixel width you’ll be able to see all of the lux levels at once without horizontal scrolling. Better yet, the iPad, iPhone, and most Android Tablets and Smartphones will display all (or almost all) of the 64 screen shots on a single page in Portrait mode – you might need to pinch in the image to see a single screen view. The Master Photo Grid is the best way to see the large scale trends and differences in how the Tablet and Smartphone displays degrade as the ambient lighting increases outdoors. Be sure to read the detailed analysis for the lux levels and Tablets below.

 

 

Range of Ambient Lighting

Our eyes have a tremendous dynamic range because everyday we experience a tremendous range of ambient lighting levels from absolute darkness (0 lux) up through direct sunlight (120,000 lux). Tablets and Smartphones, as mobile devices, must be viewed under this incredible range of ambient light. Ambient light levels are measured in lux, which is a Lumen per square meter. Below is a list of representative lux levels. The values and ranges are approximate and can vary based on the situation particulars including location, orientation, time of day, and time of year. The outdoor levels are for sunlight at noon.

 

Table 1.  Ambient Lighting Levels

 

Tablets and Smartphones tend to be held at angles that pick up more of the surrounding ambient light than the more vertically oriented screens in laptops, desktops, and HDTVs. On the other hand, for Tablets and Smartphones in many cases you can change your orientation, location, and viewing angle to reduce the amount of light being picked up by the screens.

 

 

High Ambient Light Contrast Ratings for the Tablets

There aren’t any measured quantitative specs that help evaluate display performance in high ambient lighting other than the DisplayMate Contrast Rating for High Ambient Light values that are included in all of our Mobile Display Technology Shoot-Out articles. On the other hand, consumers and manufacturers are obsessed with Contrast Ratios and display Black Levels, which are both measured in absolute darkness. While these specs are excellent for HDTVs in dark home theaters, they are for the most part irrelevant for Tablets and Smartphones because the ambient light reflected from their screens generally exceeds the display’s own internal Black Level glow.

 

The actual image contrast, screen visibility, and readability depends on a combination of both the display’s Brightness and the screen’s Reflectance. The higher the Brightness and the lower the screen Reflectance the easier it is to see the screen. The DisplayMate Contrast Rating for High Ambient Light is defined as the ratio of Peak Brightness (Luminance in cd/m²) to the Average Screen Reflectance (in percent). Below we list the Peak Display Brightness, Screen Reflectance, and DisplayMate Contrast Rating for High Ambient Light for each of the tested Tablets. Links are provided to the articles with the measurements.

 

Table 2.  High Ambient Light Contrast Ratings

 

Note that the Contrast Rating for High Ambient Light varies by almost 3 to 1 for the above Tablets. The variable range for the Motorola Xoom results from its use of Dynamic Brightness that varies with the Average Picture Level of the image content – a bad idea because it decreases both picture quality and screen visibility.

 

 

Lab Screen Photographs and Measurements with Ambient Lighting

In the Screen Photographs sections below we visually compare the Tablet display’s visibility and image contrast. There are two sets: The first set shows the 4 Tablets side-by-side for each individual lux level so you can directly compare their relative performance. The second set shows all of the lux levels together for each of the Tablets individually, so you can see how rapidly each Tablet degrades with ambient light.

 

The screen photographs were all taken inside a large Integrating Hemisphere that uniformly illuminates the screen in all directions with a powerful daylight 6500 Kelvin light source. Missing from the Lab photos are the superimposed images you would see of your face and surrounding objects that are embedded within the screen reflections. The Tablets were all set to their Maximum Brightness and the Ambient Lighting Levels were measured with a Konica Minolta T-10M Illuminance Meter. We used one of our proprietary DisplayMate Ambient Light Test Patterns with 10 scales in 8 colors (including gray/white) each with 25 intensity steps. As the Ambient Light Level increases you will be able to make out fewer and fewer of the intensity steps. The two Reverse Scales make it possible to count the number of invisible or barely visible steps. Tablets with a larger High Ambient Light Contrast Rating will show more of the Intensity Scale at a given lux level. The more steps you can see the better the Tablet display.

 

Important Note for Viewing All of the Photos:

The photos are all taken with the camera’s automatic exposure, which will vary based on the total brightness of the image (display plus reflected light). That’s the same way your eyes process all images. The borders between the photos are at true Black. Use them to compare the Black Levels in the photos. All of the photos are taken at the display’s maximum brightness setting, which is also its maximum power setting. The visibility of image content will decrease at lower settings. Most Automatic Brightness Controls will significantly lower the display brightness settings below 5,000 lux in order to save power and increase the running time on battery. It’s a challenging compromise that all current Automatic Brightness Controls perform poorly…

 

 

Lab Screen Photographs with Ambient Lighting for all Tablets Side-by-Side

Comparisons of the Apple iPad 2, Amazon Kindle Fire, Motorola Xoom, and Samsung Galaxy Tab 10.1.

The lux level descriptions are representative. Refer to the Ranges listed in Table 1 above for an overview.

Click on any of the links below for a specific lux level or just view them all in order.

 

0 lux 300 lux 1,000 lux 2,000 lux 5,000 lux 10,000 lux 20,000 lux 40,000 lux

Absolute Darkness Moderate Indoor Lighting Bright Indoor Lighting Outdoor Lighting in Heavy Shade Moderate Overcast Sky  or  Direct Sunlight in Heavy Shade Moderate Outdoor Daylight Full Daylight Not in Direct Sunlight  or  Indirect Indoor Sunlight Indirect Outdoor Sunlight

 

Lab Screen Photographs for each Individual Tablet from 0 lux to 40,000 lux

These are the same Screen Photographs arranged by individual Tablet rather than by Ambient Light lux level.

Click on any of the links below for a specific Tablet or just view them all in order.

 

Apple iPad 2 Photos  –  from 0 lux to 40,000 lux

Amazon Kindle Fire Photos  –  from 0 lux to 40,000 lux

Motorola Xoom Photos  –  from 0 lux to 40,000 lux

Samsung Galaxy Tab 10.1 Photos  –  from 0 lux to 40,000 lux

 

Master Photo Grid Summary

The Master Photo Grid has all of the Screen Shots for the Tablets and Smartphones under Ambient Lighting in a compact format. When viewing on displays with at least 1920 pixel width you’ll be able to see all of the lux levels at once without horizontal scrolling. Better yet, the iPad, iPhone, and most Android Tablets and Smartphones will display all (or almost all) of the 64 screen shots on a single page in Portrait mode – you might need to pinch in the image to see a single screen view. The Master Photo Grid is the best way to see the large scale trends and differences in how the Tablet and Smartphone displays degrade as the ambient lighting increases outdoors. Be sure to read the detailed analysis for the lux levels and Tablets below.

 

 

Lab Screen Photographs with Ambient Lighting for all Tablets Side-by-Side

Comparisons of the Apple iPad 2, Amazon Kindle Fire, Motorola Xoom, and Samsung Galaxy Tab 10.1.

The lux level descriptions are representative. Refer to the Ranges listed in Table 1 above for an overview.

 

0 lux  –  Absolute Darkness

In absolute darkness you will see the best picture quality with the best color, image contrast, and gray scale accuracy that the display can produce. There is no ambient light to wash out the colors, intensities, and image contrast on the display. If you are a purist obsessed with Black Levels and Contrast Ratios this will either be your best or most irritating viewing conditions. Be sure to significantly lower the Brightness setting of the display in order to reduce eye strain. For LCDs, this will also significantly lower the visibility of the annoying Black Levels (they will already be close to zero for OLED displays). All 4 of the tested Tablets have LCD displays. But… the eye’s light sensitivity increases in the dark so you will actually notice the Black Levels more when viewing dark images in the dark. At slightly higher Ambient Lighting (below) the Black Levels will become less noticeable – this is referred to as Bias Lighting.

 

 

 

300 lux  –  Moderate Indoor Lighting

At the moderate indoor ambient light levels the images should appear only slightly degraded from the 0 lux images that are shown above. The images should show very good color, image contrast, and gray scale accuracy. There is not much ambient light to wash out the colors and contrast on the display, but the Screen Reflectance is already larger than each of the display’s own Black Level.

 

 

 

1,000 lux  –  Bright Indoor Lighting

At the bright indoor ambient light levels the images appear noticeably degraded from the 0 lux and 300 lux images above. The images should still show satisfactory color, image contrast, and gray scale accuracy. The ambient light is starting to noticeably wash out the colors and image contrast on the display. The images on the iPad and Galaxy Tab are not as washed out as on the Kindle Fire and Xoom due to their larger Contrast Rating for High Ambient Light.

 

 

 

2,000 lux  –  Outdoor Lighting in Heavy Shade

At outdoor lighting in heavy shade ambient light levels the images appear more degraded than the 1,000 lux images above. The ambient light is noticeably washing out the colors and image contrast on the display. The images on the iPad and Galaxy Tab are not as washed out as on the Kindle Fire and Xoom due to their larger Contrast Rating for High Ambient Light.

 

 

 

5,000 lux  –  Moderate Overcast Sky  or  Direct Sunlight in Heavy Shade

For moderate overcast sky ambient light levels the images appear significantly degraded from the previous sets. This lux level also corresponds to the shadow cast by a person in direct sunlight that falls on the display screen they are viewing. The images are showing significantly reduced color, image contrast, and gray scale accuracy. The ambient light is significantly washing out the colors and image contrast on the display. The images on the iPad and Galaxy Tab are not as washed out as on the Kindle Fire and Xoom due to their larger Contrast Rating for High Ambient Light.

 

 

 

10,000 lux  –  Moderate Outdoor Daylight

For moderate outdoor daylight ambient light levels the images appear substantially degraded. The images show large reductions in color, image contrast, and gray scale accuracy. The high ambient light is substantially washing out the colors and image contrast on each display. The images on the iPad and Galaxy Tab are not as washed out as on the Kindle Fire and Xoom due to their larger Contrast Rating for High Ambient Light.

 

 

 

20,000 lux  –  Full Daylight Not in Direct Sunlight  or  Indirect Indoor Sunlight

For full daylight not in direct sunlight or indirect indoor sunlight ambient light levels these images are barely visible. The images on the iPad and Galaxy Tab are not as washed out as on the Kindle Fire and Xoom due to their larger Contrast Rating for High Ambient Light.

 

 

 

40,000 lux  –  Indirect Outdoor Sunlight

At the indirect outdoor sunlight ambient light levels these images are almost invisible. The images on the iPad and Galaxy Tab are not as washed out as on the Kindle Fire and Xoom due to their larger Contrast Rating for High Ambient Light.

 

 

 

Lab Screen Photographs for each Individual Tablet from 0 lux to 40,000 lux

These are the same Screen Photographs arranged by individual Tablet rather than by Ambient Light lux level.

 

Apple iPad 2  –  from 0 lux to 40,000 lux

Peak Brightness  :  410 cd/m²

Average Screen Reflectance  :  8.7 percent

High Ambient Light Contrast Rating  :  47

 

 

 

Amazon Kindle Fire  –  from 0 lux to 40,000 lux

Peak Brightness  :  354 cd/m²

Average Screen Reflectance  :  14.8 percent

High Ambient Light Contrast Rating  :  24

 

 

 

Motorola Xoom  –  from 0 lux to 40,000 lux

Peak Brightness  :  257 to 410 cd/m²  (Dynamic Brightness)

Average Screen Reflectance  :  13.0 percent

High Ambient Light Contrast Rating  :  20 to 31

 

 

 

Samsung Galaxy Tab 10.1  –  from 0 lux to 40,000 lux

Peak Brightness  :  464 cd/m²

Average Screen Reflectance  :  8.2 percent

High Ambient Light Contrast Rating  :  57

 

 

 

Master Photo Grid Summary

The Master Photo Grid has all of the Screen Shots for the Tablets and Smartphones under Ambient Lighting in a compact format. When viewing on displays with at least 1920 pixel width you’ll be able to see all of the lux levels at once without horizontal scrolling. Better yet, the iPad, iPhone, and most Android Tablets and Smartphones will display all (or almost all) of the 64 screen shots on a single page in Portrait mode – you might need to pinch in the image to see a single screen view. The Master Photo Grid is the best way to see the large scale trends and differences in how the Tablet and Smartphone displays degrade as the ambient lighting increases outdoors. Be sure to read the detailed analysis for the lux levels and Tablets above.

 

 

About the Author

Dr. Raymond Soneira is President of DisplayMate Technologies Corporation of Amherst, New Hampshire, which produces video calibration, evaluation, and diagnostic products for consumers, technicians, and manufacturers. See www.displaymate.com. He is a research scientist with a career that spans physics, computer science, and television system design. Dr. Soneira obtained his Ph.D. in Theoretical Physics from Princeton University, spent 5 years as a Long-Term Member of the world famous Institute for Advanced Study in Princeton, another 5 years as a Principal Investigator in the Computer Systems Research Laboratory at AT&T Bell Laboratories, and has also designed, tested, and installed color television broadcast equipment for the CBS Television Network Engineering and Development Department. He has authored over 35 research articles in scientific journals in physics and computer science, including Scientific American. If you have any comments or questions about the article, you can contact him at dtso.info@displaymate.com.

 

About DisplayMate Technologies

DisplayMate Technologies specializes in proprietary sophisticated scientific display calibration and mathematical display optimization to deliver unsurpassed objective performance, picture quality and accuracy for all types of displays including video and computer monitors, projectors, HDTVs, mobile displays such as smartphones and tablets, and all display technologies including LCD, OLED, 3D, LED, LCoS, Plasma, DLP and CRT. This article is a lite version of our intensive scientific analysis of Tablet and Smartphone mobile displays – before the benefits of our advanced mathematical DisplayMate Display Optimization Technology, which can correct or improve many of the display deficiencies. We offer DisplayMate display calibration software for consumers and advanced DisplayMate display diagnostic and calibration software for technicians and test labs.

 

For manufacturers we offer Consulting Services that include advanced Lab testing and evaluations, confidential Shoot-Outs with competing products, calibration and optimization for displays, cameras and their User Interface, plus on-site and factory visits. See our world renown Display Technology Shoot-Out public article series for an introduction and preview. DisplayMate’s advanced scientific optimizations can make lower cost panels look as good or better than more expensive higher performance displays. For more information on our technology see the Summary description of our Adaptive Variable Metric Display Optimizer AVDO. If you are a display or product manufacturer and want to turn your display into a spectacular one to surpass your competition then Contact DisplayMate Technologies to learn more.

 

Article Links:  Smartphone Displays Under Bright Ambient Lighting Shoot-Out

Article Links:  Mobile Brightness Photo Grid Under Bright Ambient Lighting

Article Links:  Smartphone Automatic Brightness Controls and Light Sensors

 

Article Links:  Tablet Display Technology Shoot-Out

Article Links:  Smartphone "Super" LCD-OLED Display Technology Shoot-Out

 

Article Links:  Mobile Display Shoot-Out Article Series Overview and Home Page

Article Links:  Display Technology Shoot-Out Article Series Overview and Home Page

 

 

Copyright © 1990-2012 by DisplayMate Technologies Corporation. All Rights Reserved.

This article, or any part thereof, may not be copied, reproduced, mirrored, distributed or incorporated

into any other work without the prior written permission of DisplayMate Technologies Corporation