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Contrast ratio of OLED modules

Grinder

New member
The contrast ratio for the many of the Crystalfontz OLED modules is shown as 100:1.

Generally in this category,the contrast ratio for competitors OLEDs varies from 1000:1 to 2000:1.

Why there is a huge difference in contrast ratio?

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CF Tech

Administrator
The contrast ratio is essentially a measure of how dark an "off" pixel is. The brightness of an "on" pixel is specified separately.

CR = (brightness_of_lit_pixel)/(brightness_of_dark_pixel)

For an LCD, the dark pixels are not truly dark (some light always "leaks" through), so the above equation makes sense.

The contrast ratio (CR) used for OLED is "dark room" contrast.

For an OLED, a dark pixel is truly 100% off. The LED is off an no light is made in it at all. The only light coming from a dark pixel might be some reflection from the room. So if your room is perfectly dark and your measuring equipment is good:

brightness_of_dark_pixel will approach 0

so:

CR will approach infinity!

The result is that dark room contrast ratio is pretty much a useless measure for OLED displays.

Any OLED display has good dark room contrast.

We use CR = 100, because that is a good contrast ratio for LCD and CRT, and OLED have good contrast.

Here is a snippet from Wikipedia on the subject of dark room contrast (bold added):
Dark-room contrast

In order to measure the highest contrast possible, the dark state of the display under test must not be corrupted by light from the surroundings, since even small increments ΔL in the denominator of the ratio (LH + ΔL) / (LL + ΔL) effect a considerable reduction of that quotient. This is the reason why most contrast ratios used for advertising purposes are measured under dark-room conditions (illuminance EDR ≤ 1 lx).

All emissive electronic displays (e.g. CRTs, PDPs) theoretically do not emit light in the black state (R=G=B=0%) and thus, under darkroom conditions with no ambient light reflected from the display surface into the light measuring device, the luminance of the black state is zero and thus the contrast becomes infinity.

When these display-screens are used outside a completely dark room, e.g. in the living room (illuminance approx. 100 lx) or in an office situation (illuminance 300 lx minimum), ambient light is reflected from the display surface, adding to the luminance of the dark state and thus reducing the contrast considerably.

A quite novel TV-screen realized with OLED technology is specified with a dark-room contrast ratio CR = 1.000.000 (one million). In a realistic application situation with 100 lx illuminance the contrast ratio goes down to ~350, with 300 lx it is reduced to ~120 [6].
 
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