Your phone display’s brightness consumes up to half of its power. And likelihood is that it’s being horribly mismanaged, owing to bad engineering and a backwards user interface. Here, Dr. Raymond Soneira of DisplayMate explains Brightnessgate for iPhone 4 and Android.

Although consumers currently don’t pay much attention to them, the Automatic Brightness control and lightweight Sensor on smartphones has a first-rate impact on displayed image quality, screen viewability and readability, in addition as preventing eye strain and headaches when the screen is simply too bright or too dim for the current level of ambient lighting, which varies considerably. But for plenty of consumers, organizations and even governments, it truly is their impact on power consumption that generates the greatest concerns and emotions.

As we’ll demonstrate below with extensive lab measurements, brightness controls are a sham of incredibly poor design and engineering-Automatic Brightness in an excellent majority of smartphones being effectively useless. And because they don’t work properly consumers simply turn them off altogether, making matters even worse for power use, screen readability and viewing comfort. This deserves to be called Brightnessgate-a scandal with several causes.

How Automatic Brightness Works-In Principle

Smarphones have a lightweight sensor located inside the bezel right next to the screen that measures the ambient light along side control software that appropriately raises or lowers the screen brightness based on the measured light level. If you find yourself watching at the hours of darkness the screen must be appropriately dim. When the ambient light level is higher the screen must be made appropriately brighter for two reasons: as a result of glare from ambient light reflected off the screen, which washes out the image, and because the eye’s light sensitivity decreases substantially as the ambient light level increases. Unfortunately, none of the above currently works properly in smartphones for the subsequent reasons:

The Light Sensor

In a smartphone the light sensor is facing your head and is measuring the brightness of your face rather than the ambient light level that’s behind and to each side of the phone, that is what actually sets your eye’s light sensitivity and what need to be determining the brightness level of the screen. The present front-facing light sensors are good for measuring and correcting the image for glare from screen reflections (by modifying the display transfer functions), but not for setting the screen brightness. To do this in smartphones a rear and side facing ambient light sensor with a distinct angular profile than the current Illuminance sensors is needed for future hardware designs. Note that a front sensor for glare seriously isn’t as important since screen reflectance will probably be very low-around 5 percent for plenty of smartphones. See Part I of this text.

Automatically Adjusting the Brightness

The screen brightness ought to be set carefully and systematically based on the info from the light sensor. Here the smartphones fail again with poor and even bizarre behavior that we document below. Another sign of careless engineering-all three of the smartphones that we tested have operational bugs or errors with their Automatic Brightness. One essential feature missing from smartphones is allowing users to interactively adjust the display for their own visual preferences on how the screen brightness should vary as the ambient light changes-and it may be accomplished automatically as we’ll outline below. Some people and applications prefer a brighter or dimmer screen, and some individuals are willing to position up with a dimmer screen that will not be as easy or comfortable to read-in return for longer battery running times. So it’s important to implement a properly functioning Automatic Brightness that automatically adapts to the user’s own brightness preferences-otherwise will probably be disabled by the user.

Results Highlights

Here are the foremost results from our extensive labs tests and viewing tests on three smartphones that we performed to guage the Automatic Brightness Controls and lightweight Sensors under a variety of ambient lighting conditions.

Determining the Optimum Screen Brightness

The first step in evaluating Automatic Brightness is to choose how the screen brightness should change with ambient light level for maximum viewing. To demonstrate the correct relationship I read an editorial from the most recent York Times on the iPhone 4 under quite a lot of ambient lighting conditions. I turned Auto-Brightness Off and then manually adjusted the screen brightness for my own optimum viewing comfort-not too dim, not too bright, best-for each of 7 different ambient light levels, from total darkness up through moderate outdoor lighting levels. After each reading I measured the Ambient Light Brightness (Illuminance in lux) and the screen’s Brightness (white Luminance in cd/m2). The consequences appear as the black data points in Figure 1 together with a solid black trend line. At about 1,000 lux (that’s at the low end of outside lighting levels) I reached the maximum screen brightness for the iPhone 4, that’s 541 cd/m2-it can be the brightest mobile display I actually have ever measured, but above 1,000 lux the iPhone 4 can’t provide as much screen brightness as I want to have. The screen continues to be readable way past 10,000 lux (that is full daylight that isn’t in direct sunlight) nevertheless it gets increasingly hard to comfortably make out the contents of the screen at the higher ambient light levels.

The optimum screen brightness values will vary as a consequence of personal preferences, and likewise with screen size and viewing distance, but the proportional linear increase with ambient brightness indicated by the cast black line in Figure 1 need to be similar for everyone. The dashed black lines in Figure 1 also show quite a lot of alternative brightness relations-the dashed lines labeled Dim and extremely Dim are for aggressive power savings at high ambient lighting or for folk with more sensitive eyes, and the intense relation is for folk or applications that need particularly high screen brightness with ambient light. We’ll explain methods to automatically implement all of this functionality below. Now let’s take a look at the Apple iPhone 4 and two Android phones (Samsung Galaxy S and HTC Desire) to work out how they perform.

Figure 1. The measured Screen Brightness for diverse measured Ambient Brightness levels. The manually determined optimum brightness settings are the black data points with their trend line. The values for five different Auto-Brightness slider settings of the iPhone 4 are labeled Auto Minimum to Maximum. Circles are the information points. The dashed lines show a variety of alternative brightness relations. The graph is linear from 0 to 2,000 lux and then jumps in steps to 10,000 and 100,000 lux. The labels from Pitch Black to Direct Sunlight roughly identify the lux levels associated with them. The maximum Luminance of the iPhone 4 is 541 cd/m2.

iPhone 4 Auto-Brightness

Next, I turned Auto-Brightness On and then measured the screen brightness (white Luminance cd/m2) that the iPhone 4 produces under quite a lot of ambient light levels, from 0 lux (Pitch Black) up through 100,000 lux (Direct Sunlight). When Auto-Brightness is turned On the Brightness slider adjusts the automobile behavior to allow consumers (in principle) to set their own individual screen brightness preferences for ambient light. To judge this, I measured 5 different settings of the slider: Maximum, ¾, ½ (center), ¼ and Minimum. The implications are plotted as the colored lines in Figure 1 – the circles are the measured data values. None of the automobile Brightness settings even remotely approaches the required behavior discussed above. It certainly looks like nobody at Apple ever bothered to set or check Auto-Brightness for useful performance, that’s why there are numerous user comments questioning how it works on the web… This can be Brightnessgate for the iPhone.

The iPhone 4 comes from the factory with the Brightness slider set to ½ (center) and with Auto-Brightness turned On. At 2,000 lux, where practically everyone will want the display operating at maximum brightness, Auto-Brightness sets it to simply 60 percent of extreme, so Auto-Brightness is throwing away 40 percent of the valuable brightness needed for screen visibility. And at 10,000 lux, that is full daylight, the screen brightness continues to be below 90 percent of utmost. The ¾ setting is far too bright and gear wasteful for all indoor viewing and yet it still throws away 20 percent of the screen brightness at 2,000 lux for outside viewing. The Maximum setting is useless because it varies the screen brightness (and gear) by under 10 percent and the ¼ and Minimum settings are far too dim to be useful for humans.

The iPhone 4 Auto-Brightness performs in a bizarre fashion where it typically makes the screen too bright at lower indoor ambient light levels (that’s important for saving battery power) and too dim at higher outdoor levels (that is important for screen readability) – it’s always wrong, usable but very inefficient and wasteful. But Brightnessgate for the iPhone gets even worse.

iPhone 4 Auto-Brightness Bug

One behavior of the iPhone 4 Auto-Brightness that could be a serious operational error or bug is that it locks onto the brightest ambient light sensor value that it has measured at any point starting from the time it was turned on, and then continues to take advantage of that highest value indefinitely to set the screen brightness until the display turns off – either by cycling through sleep mode or full power off. Because of this the screen brightness will likely be set too high, which wastes power and may cause eye strain while you move to lower ambient light levels. Auto-Brightness should follow the current ambient light level (with appropriate time averaging and filtering). Apple should correct this with a software update. To easily verify this behavior along with your own iPhone activate Auto-Brightness under Settings and set the Brightness slider near the middle of its range. Go to a extremely dark location. Click the sleep/wake button on the pinnacle of the phone to turn the display off. Then wake it up with the sleep/wake button or the Home button. Note the screen brightness at midnight. Now take the phone to an awfully bright outdoor location (equivalent to in direct sunlight) then go back (with the display on) in your original dark location and monitor the screen brightness. The display will remain at very high brightness indefinitely until the iPhone enters sleep mode again (or runs out of battery). What’s even more shocking is that Brightnessgate is even worse on Android phones.

Figure 2. The measured Screen Brightness for diverse measured Ambient Brightness levels for the Samsung Galaxy S and HTC Desire. The Manual Optimum relation and other elements are almost like in Figure 1.

Android Automatic Brightness

There are currently a mess smartphones running Google’s Android OS, and all the models that we have got looked at appear to work inside the same way. There is a slider for manual adjustment of screen brightness, but when Automatic Brightness is enabled the slider disappears and there aren’t any user settings or preference adjustments (unlike the iPhone 4) – you get whatever screen brightness settings Android and the smartphone manufacturers have pre-programmed into them. Unfortunately, those Automatic Brightness settings are incredibly primitive and crude – on the Samsung Galaxy S and HTC Desire that we lab tested Automatic Brightness produces only four fixed screen brightness levels when the ambient lighting changes from pitch black your entire way up to direct sunlight, with each manufacturer setting their own breakpoints as shown in Figure 2. Hence alone, Auto Brightness is effectively useless for Android. But Brightnessgate on Android gets even worse.

Android Automatic Brightness Bugs

Both of the Android phones we lab tested have their own Auto Brightness operational errors or bugs. On the Samsung Galaxy S two of the four Android Automatic Brightness levels are set ridiculously high: 7,000 and 30,000 lux – they’re about a factor of 10 too high to be useful. The Galaxy S screen brightness remains at an exceedingly low 170 cd/m2 up until near Full Daylight, only about 50 percent of the screen brightness that it could actually deliver, and it waits up until almost Direct Sunlight to head up to it’s maximum screen brightness of 305 cd/m2. Since there aren’t any available settings or adjustments it’s better to depart the Automatic Brightness permanently off until this gets fixed with a software update. The HTC Desire has a somewhat better option of brightness level breakpoints than the Galaxy S, nonetheless it has a bug the same as the iPhone – once the light sensor detects a lightweight level over 100 lux it won’t allow the screen below Android brightness Level 2 until the display is cycled off by going into sleep mode using the facility button or Screen timeout.

Conclusion for the Current Auto Brightness

Automatic Brightness on existing smartphones is almost functionally useless because the manufacturers have not made the hassle required to develop, evaluate and test the software and hardware in order that they work properly and effectively. All the models we tested also have serious operational errors and bugs indicating how little an effort has been made to cause them to work (or rather not work) properly. It’s clear that almost all manufacturers are using ad hoc implementations other than methodical science and engineering, that’s shameful and shocking… In consequence most smartphones are operating without Auto Brightness because consumers disable them after they don’t work properly, which means that the screen brightness is seldom set correctly for the big variety of ambient lighting conditions that almost all smartphones experience. It also implies that the display is extremely likely set by the shopper to a perpetual high screen brightness. Consequently the battery runs down much earlier than if the brightness and tool were actively and intelligently managed automatically, as they ought to be. We outline tips to do this next.

How Automatic Brightness Should Work

We’ve already shown that Automatic Brightness is very important and is currently functionally useless on smartphones for plenty reasons. We’ve also discussed the various changes needed for the Ambient Light Sensors, but by far the largest factor is getting the user interface for screen brightness to work properly so that customers can use it to adjust the screen brightness based on their lonesome visual preferences, in a natural fashion that automatically implements and tweaks the screen brightness they’d wish to see for different ambient lighting conditions. That may maximize viewing comfort, screen readability, energy efficiency and battery run time if it’s done correctly.

Right now the user interface for brightness controls is absolutely backwards-the Light Sensor measures the ambient light and the smartphone or HDTV adjusts the screen brightness based on some ad hoc and mysterious algorithm based on an earlier user setting of a brightness control. The solution is intensely simple – do it within the opposite way – the shopper initially adjusts the screen brightness manually to whatever they need for the current ambient lighting. The Ambient Light Sensor then measures this light level. The worth is recorded and used to interpolate the screen brightness whenever the ambient lighting changes. In principle, only two such user settings are needed to train the Automatic Brightness for a linear interpolation as shown in Figure 1. Whenever the user doesn’t find the current screen brightness to their liking, they manually tweak the brightness and the most recent value and ambient light level are used to update the automobile Brightness calibration.

There is a different thing. To make this work smartphones desire a convenient brightness control to tweak and trainside the Automatic Brightness. Every smartphone in the solar system has a convenient Volume Control but almost always you need to go down multiple menu levels to get to a cumbersome Brightness Control. My suggestion for all smartphones: temporarily shift the amount buttons to Brightness buttons by pressing both the + and – buttons collectively – in an effort to activate a brief Brightness Shift. It’s fast, convenient and simple, and then have them automatically day out and shift back to Volume Controls once you’re done adjusting the brightness. Every display needs a convenient external Brightness Control – not buried under several levels of menus. In all cases it’s best to implement it using the present Volume Control along side a suitable shift button.

The above is absolute to work nicely and conveniently for all consumers, solve Brightnessgate, maximize viewing comfort, screen readability, energy efficiency and battery run time all together. I’m hoping the manufacturers are listening.

Special Because of Jay Catral and Konica Minolta Sensing for their instruments and technical support. To measure the Ambient Light Brightness (Illuminance in lux) we used a Konica Minolta T-10 Illuminance Meter and for screen Brightness (Luminance in cd/m2) we used a Konica Minolta CS-200 ChromaMeter .

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 an extended-Term Member of the area famous Institute for Advanced Study in Princeton, another 5 years as a Principal Investigator within the Desktops 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. When you’ve got any comments or questions on the thing, you may contact him at dtso@displaymate.com .

Source

This post is tagged: ambient light level, automatic brightness control, brightness controls, eye strain and headaches, light sensitivity, screen readability