Glare and reflection are terms that are often confused. Both anti-glare and anti-reflective enhancements attempt to improve or optimize readability while using different techniques to address the causes of reduced readability due to external ambient light sources.
Anti-glare deals with external sources of reflection off a surface – like bright sunlight or high ambient lighting conditions – by using diffusion to disperse the reflected light from the surface. Diffusion works by reducing the coherence of the image that is reflected on the screen, making this unwanted image unfocused to the user’s eye, and thereby mitigating its interference with the viewing of the intended image. This comes at the sacrifice of clarity and resolution of the intended image. While economical to apply, the trade-off in image clarity caused makes anti- glare an inferior solution to anti-reflection.
Unlike the diffusion-based anti-glare solutions, anti-reflection takes into account both internal and external sources of accumulated reflection. As light passes from one medium to another, the difference between the index of refraction in the adjacent surfaces creates transitional phase difference, which increases the amount of light reflected. These reflections are cumulative and cause the display to become “washed out,” which reduces the contrast and the overall readability of the LCD display. The anti-reflective coatings consist of transparent, thin film structures with alternating layers of contrasting refractive index, which results in destructive interference in the light reflected from the interfaces, and constructive interference in the corresponding transmitted light.
A typical amorphous silicon TFT LCD exhibits a contrast of approximately 300 to 700 in a dark room transmissive mode measurement. The contrast on the same unit measured under ambient illumination is drastically lowered due to surface reflection or glare. A standard 200 NIT LCD display measured in a dark room may have a 300:1 contrast ratio, but could then measure less than 2:1 in direct sunlight. This is due to the fact that the surface glare increases the luminance by over 200 NITs, both on the “white” and the “black” that are produced on the display screen. Resulting luminance of the white is slightly over 400 NITs and the luminance of the black is slightly over 200 NITs, causing the contrast ratio to then drop to less than 2:1 and the picture quality to become drastically reduced.