Panasonic KX-TU301

The Panasonic has a bright OLED display

What does “easy to see” mean? As a thing to do it’s quite obvious, but as a thing to build it’s a lot less so. Just as building an easy to hear mobile phone isn’t only about volume, an easy to see mobile phone isn’t just about big buttons and a big screen. This things matter of course, but it’s got a lot of subtleties.

If we start with Liquid Crystal Displays there are two types STN and TFT. They both work by polarising light, but STN works better with light bounced off the display from the front and TFT better with light shone through from the backlight. This means that “easy to see” depends on how bright the ambient light is. On a sunny day in strong light an STN will be better, but unless the is very strong light TFT will look better. How much better will depend on the ambient lighting and the strength of the backlight. Since most mobile phones are sold indoors, TFT nearly always looks better in a  phone shop.

STN also has muddier colours but it’s a lot cheaper to make. We can however see that the choice isn’t that clear-cut. There is a third, similar technology which is OLED. This stands for Organic Light Emitting Diode. The light in this doesn’t come from a backlight as with LCD but from the crystals which make the display. It produces brighter, higher contrast colours and because it doesn’t need a backlight is a lot thinner. OLED however is quite a lot more expensive to make. The only phone Fuss Free Phones sells with OLED is the Pansonic KX-TU301.

Screen technology moves at a disappointingly slow pace. Getting  a new technology into production usually requires a hundreds of millions of pounds in investment, not least in building new factories. This means that new technologies which are “coming soon” or “just around the corner”, can take much longer to appear than we are used to in the fast moving world of mobiles.

One of the technologies which best demonstrates this is e-ink. It’s started to appear more widely in the last few years, first in the Motorola F3 phone and then in the Amazon Kindle. What marks e-ink out as an easy to see technology is the amazing contrast. It’s much more like looking at ink on paper than any of the other technologies. Unlike LCD it can’t be backlit but it has a number of other advantages, it’s thin and amazingly low power. E-ink only needs a tiny bit of electricity to change from on to off and no power at all to retain an image. This makes it ideal for displays on the top of a clamshell phone. E-ink unfortunately only currently works in black and white. There are some promising technologies from Fujitsu and the American company Kent displays based on a technology called cholesteric LCD, and from Cambridge Display technologies which uses polymer organic light emitting diodes but these have all been just around the corner for ten years.

Colour is important because you can do better, high contrast displays with colours. Microsoft Windows has a high contrast mode that uses yellow on black. There was some NASA research around the Apollo Program which showed that the four colours which worked best in combination were a light blue, orange, black and white. They however were building displays for astronauts with perfect vision. How well this works on people with diminished vision isn’t known but it’s a starting point.

For the moment the best technology for easy to use phones is e-ink for black and white, and OLED for colour. Fortunately we are seeing huge growth in both of these technologies for e-readers and smartphones so for us the future looks bright.