Nokia’s ClearBlack Display (CBD): technology explained
In September 2010, Nokia has announced the ClearBlack Display (CBD) technology. CBD adds a reflection-blocking polarizer layer between the touch layer and the display panel. CBD displays blocks incoming light reflections and so perform better under direct sunlight.
CBD is not the same as a Super-AMOLED display (which is an AMOLED with a touch-panel built-in). CBD can be added to an AMOLED display or an LCD one. In the photo below, we can see a normal C6-01 phone with a CBD display (on the left) and the same phone without the CBD layer (on the right):
How do CBD displays work?
Here's Nokia explanation of how CBD works: A CBD filter includes both a linear polariser and retardation layers between the surface of your phone and the display. When light hits your screen, this is what happens:
- It hits the linear polariser, this vertically polarises the light. (Polarising means roughly aligning the wave vibration in a particular direction).
- Then it hits the circular polariser retardation layer. This converts the light again, making it right-circularly polarised.
- Then it hits the screen and bounces off it, switching the rotation of the light to leftist.
- It goes back through the retardation layer. When this happens, the light becomes horizontally polarised.
- Finally, it hits the linear polariser, since the light is horizontally polarised at this point it can be blocked entirely by this optical solution.
So why doesn't the light from your phone’s display get blocked? Because it only goes through the second half of this journey so the light is unpolarised when it hits the final filter and goes through.
CBD smartphones
Nokia has announced several AMOLED phones that has CBD displays: the E7 and the C6-01, the X7, the N9 and the Lumia 710, Lumia 800 and Lumia 900. All CBD displays except the one in the Lumia 710 were AMOLED ones.
Nokia E7
Engadget really liked the CBD displays: "The screen is simply gorgeous -- ClearBlack may be a gimmicky trademark, but CBD's black levels are no joke. We're definitely talking Super AMOLED degrees of awesome...". Engadget also put it to the test against Apple's S-LCD retina-display. They say that the iPhone's display has a "noticeable blue warmth" and wasn't as vibrant or bright as the AMOLED, which was a bit oversaturated.
In the photo above, you can see the Nokia's E7 (left) vs a Galaxy S with a Super-AMOLED.
Clear Black Displays today
Nokia stopped producing CBD displays many years ago, the last device to sport a CBD display was likely Nokia's Lumia 900 Windows Mobile Device. Today OLED displays provide excellent sunlight visibility, using several technologies.
