LCD Technicalities: Do Contrast Ratios Matter?

Problem Of The Day No. 3: Contrast Ratios

While it took a while before buyers learned of the importance of response time, another criterion has long existed, the contrast ratio.

Ironically, this measurement may be of even less significance than the response time that the manufacturers provide.

Everything And Anything 2: Contrast Ratio And Brightness

The contrast ratio is established by contrasting the brightest white that the screen can produce with the darkest black. More specifically, it is the difference in intensity between a 100% white signal and the same white signal at 0%, the result being divided by the value of a white at 0% calculated in Lux (a 0% white signal is black).

On this basis, manufacturers have deduced that the greater the contrast ratio, the better the screen, because the blacks will be darker and the whites will be "whiter", and therefore the screen will be able to distinguish between a greater number of shades of color. But that's not entirely true.

Let's examine the principle they have adopted. Basically, establishing a level of contrast means dividing the intensity of the white by the black. This means that a screen of which the maximum and minimum are respectively 200.5 cd/sq. m and 0.5 cd/sq. m would be allocated a contrast ratio of (200.5 - 0.5)/0.5 = 400: 1.

Here the contrast ratio of an LCD screen is measured by a device from Microvision , which depends upon the angle of vision.

This little calculation demonstrates that in order to obtain an impressive contrast ratio, the manufacturers have every incentive to emphasize the brightness of their screens. If, instead of 200.5 cd/sq. m, max brightness is increased to 400.5, the contrast will automatically increase to 800: 1.

However, the white will be more blinding and the black will not improve. Furthermore, there's a good chance that your eyes will not be able to tolerate such intense brightness. The screen may well produce an 800: 1 contrast ratio but it will be unusable. As a reminder, CRT screens make do with a white of 80 to 100 cd/sq. m, and the few graphic artists who have switched over to LCD screens will calibrate them to a maximum of 110 cd/sq. m.

Summary