The cause of the Nexus One diabolical battery

Having scratched my chin copiously regarding the seemingly highly variable battery life I was getting out of the Nexus One, I decided to take a closer look. First of all I powered the device from an external supply and measured the current, then I conducted tests disabling and enabling various functionality such as the wifi, GPS and so on. It seemed to be a sort of widely held belief that it was GPS that was the real killer and indeed Google Maps running with GPS with the near constant network activity due to the streaming maps is indeed just about the highest power usage I saw.

However my usage statistics showed something else, the device was using a LOT more power when I was out and about on campus. This ended up being a stronger correlation than the usage of Google Maps, although it was easy to blame Google Maps because it tended to be used during these points. What I ended up discovering was that it’s the AMOLED display on the Nexus One that is the power demo. The CPU too, if you can find ways to get it to do a lot of work, is a serious drainer. I think that CPU is better clocked at 850Mhz but the press/public latched onto Snapdragon being 1GHz so it became a marketing arms race.

The reason for the huge change in power drain was because of changing the screen brightness up to the highest level to read the screen in the bright Australian sun. I also want to make some comments on quality of display of LCD vs OLED.

Without making writing a lengthy and technical post about how the technologies work precisely, the difference between LCD and OLED is quite profound. With LCD you have a single backlight source, either fluorescent or white LEDs, and the LCD display itself cuts light making it out of the device. As opposed to OLED which has individual light sources for each pixel. Therefore it comes as no surprise to learn that LCDs use about the same power despite the display content, the only thing that changes power is the brightness of the backlight. There’s also an effect whereby LCDs can still be visable in bright light without needing to ramp up the backlight to such a level to provide a strong enough source of light to overcome the ambient light. Effectively light can bounce off the back drop that enters from outside, and not the backlight.

So what does this mean? Well, an OLED display with a largely black background uses less power because it’s not really doing too much. It’s not zero power for various reasons, but around the 30-40% mark of an LCD. It’s typically trotted out that an OLED display showing off typical program material will use less power than an LCD display. This is where things get complex and where basically the various marketing capacities of technology companies and mobile phones have chosen to measure and therefore state things in such a way that position OLED as being the all-conquering hero. It is not.

The problem for a device like a mobile phone is that you frequently will need to view something on a white background (a web site or a UI) in full daylight. Even the best OLED display is not as good as LCD as this and in order to be in the running we’re talking about 100% brightness. Under these conditions it can use 3-4 times, or more, power than an LCD. If this were rare you wouldn’t have a problem. However it’s not rare. A mobile phone goes outside and the program material often is of a bright nature. Some might be puzzled by Apple not choosing OLED on the iPad. Take a look at Apple’s UI. It’s white. An OLED display on an iPad could be catestrophically power hungry and a panel of that size would also be extrodinarily expensive.

LCD is a highly understood technology with a whole bunch of different implementations of various costs and trade-offs, of which it generally can be easier to find one which works best for a mobile device.  Apple went with an LED backlight IPS panel which is a pretty expensive choice but a very good one for image quality, brightness and wide viewing angle. There is a sub argument here on the readability of LCD versus so-called e-Ink, in general light-source displays are really bad for long viewing in low light. I wouldn’t want to read books on any LCD display.

Lastly another thing about quality of display. Anyone who has seen the display on an iPhone and a Nexus One will be left in no doubt the Nexus One has the better display. I find that the iPhone’s display in particular seems to suffer a major loss of contrast as the backlight is dropped, this is a fairly common issue with LCD and it’s also a symptom of older, cheaper, LCD technology. OLED is not immune from a reduction of image quality at lower brightnesses, in particular it has a fairly poor colour fidelity at lower brightnesses and overall like most organic LED materials, degradation is a lot more rapid than one would like.

To counteract that OLED panels are biased blue from the outset, so the faster drop-off of blue will be less noticable. That would be okay but the vendors then often bias the panel back to linear colour response, which effectively nullifies that approach. It’s possible, although I have no knowledge of this existing, that the driver circuitry could simply know hours of life and alter the colour balance to try attain a linear colour response over a greater proportion of screen life.

AMOLED displays, like the Nexus One, are certainly a bazillion times better than the previous high-res LCD displays. I’m talking as opposed to the more common QVGA like displays. I still have a HTC Touch HD which has the same resolution and size screen, more or less, and it’s not even in the same league. It is not clear to me what the ramifications are for LCD for such high resolutions. It may be that this is the reason that AMOLED is particularly suitable here, but I find it more likely that the relative rarity of displays in that resolution and size and desires to cost-cut weren’t giving LCD the run it could have.

The practical advice here for N1 owners is clear. Get a dark background on your N1 and try to avoid high brightness settings as much as you can. Conscious of the competition from high-spec Android phones it will be very interesting to see what approach Apple will take with the new iPhone. I feel certain it wont be OLED but they surely must be feeling some pressure to increase the resolution and display quality over the 3GS.

The question is whether the public love affair with OLED will vanish before OLED manages to tackle these shortcomings, or will it serve as a reminder that the old faithful LCD with some more recent innovations actually has the solution we’ve been looking for.