 OLED screens: the simple facts
Roy Johnson
The latest devices (various Samsung phones, the Microsoft Zune HD and the Google Nexus One smartphone) often boast OLED (organic light emitting diode) display screens. Why exactly are these better than the LCD screens we are used to having?
Firstly, LCD screens need a backlight – the screen itself just makes the colours and picture by filtering light coming from behind. OLED screens don’t use a backlight. That makes them thinner, lighter and much less power-hungry. Those aspects are critical for light, small, mobile devices that depend on limited battery power.
With no backlight, an OLED screen can get a better black – almost perfect. LCD screens are known for not achieving good black levels.
That brings us to the thing called contrast ratio – the higher the contrast ratio, the better the picture. In subjective terms, the image looks clearer and more “natural”. A typical LCD screen will offer anything from 10 000:1 up to 50 000:1 in contrast ratio. The best available today would be around 100 000:1. OLED screens can get up to 1 000 000:1 contrast ratios already and may improve on that.
LCD screens have problems with viewing angles – the optimum angle is perpendicular to the screen. If you are looking at them from the side, the colours or picture fades away. This is an inevitable side effect of the filtering system LCD screens use. The viewing angle for OLEDs is much better, with a near-perfect image even as far as 90º off axis.
OLED screens are much brighter than LCD because they are not filtering the light to make a picture – the screen is the picture. That is a major advantage for outdoor use.
Then there is response time. This is really how long it takes for an individual pixel to light up. What confuses people is that this aspect can be described as response time (given in milliseconds), refresh rate (usually given in cycles per second or Hertz – Hz) or even frame rate (frames per second) – this last specifically applying to video content.
Example: if the response time is 10ms, that is a refresh rate of 100Hz, giving a potential maximum frame rate of 100 frames per second for video. A typical TV or film image runs at about 25 frames per second.
Current LCD screens offer anything from 10ms to 1ms response times (100 to 1 000Hz). OLED screens do much better, with response times down to 0.01ms (100 000Hz). Why do we need it so fast? You might notice, especially on larger screens, that fast-moving objects, like a soccer ball, either make a streak or jerky image across the screen. That won’t happen when we can use higher frame rates on screens with faster response times.
Apart from potential domination of the mobile device market, OLED screens will take over TV and computer displays also, when they become affordable in larger sizes. The only OLED TV available today is the Sony XEL-1 with an 11” screen – but the picture quality is amazing. Samsung has demoed a 40” OLED HDTV and a transparent(!) OLED computer display also.
Why will this take-over happen? Because of 3D. 3D systems use much higher frame rates (greater than 140 frames per second) and they have the problem that images are darkened by whatever filter system is used. So OLED screens are the answer for 3D – faster and brighter than any LCD.
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