When you view a LCD monitor from the side, you will sometimes notice a loss of screen brightness and possibly a change of displayed colors. Manufacturers publish viewing angle specifications but what do they really mean?
Viewing angle can be one of the most confusing specifications regarding LCD monitors. Most people assume that the viewing angle is the maximum angle at which you can view an LCD Monitor without losing brightness or color shifts.
In reality, viewing angle is directly related to contrast ratio. Contrast ratio is defined as the ratio of the brightness of a white image to the brightness of a black image.
Elo TouchSystems defines viewing angle as the angle for which contrast ratio equals or exceeds a fixed value. The value may be 5:1 or 10:1. Note that straight-on "normal" viewing condition contrast ratio is typically >250:1.
For example, this figure shows a monitor with a published 140° viewing angle and a contrast ratio of 250:1.
This monitor will display a 250:1 contrast ratio when viewed head on or at a 90° angle from the surface of the monitor. The contrast ratio will decline as you view the display from the side eventually going down to 10:1 or 5:1 contrast ratio at an angle of 70° from head on. As you move away from the maximum contrast at the straight on viewing position, the brightness of the white may increase or decrease and the black may increase or decrease. However, the contrast (ratio of the two) will decrease as you move away from normal viewing. Please note, this is just a general representation and not factual for every monitor with 140° viewing angle. All values are estimates.
Other factors such as the display's brightness, ambient light and contrast conditions all play a part in the readability of the display. As mentioned above, viewing angle is defined using only the contrast ratio. However, even within this standard viewing angle, the colors or tones on the display panel may look different from the real color/tone, or they may become invisible, depending on the combination of displayed colors (background color, text color and switch color). For example, if the background color is bright and you look at the screen from below, the colors may appear inverted so that the text color and switch color darken to the point where they become invisible. Or, when the background color is dark and you look at the screen from above, the colors may again appear inverted, so that the text color and switch color brighten to the point that they become invisible. As a result, be sure to choose your screen colors carefully, so they produce an effective combination for the LCD panel's operation environment.