viewing fatigue

[Richard]

This is caused by the iris in your eye constantly being in motion as it reacts to the light output of your display. Another source is when your viewing distance creates a situation where the image occupies too small an area on the surface of the rods and cones in the back of the eyeball compared to the light level around that image. Both are caused by a display with very high light output. A bias light in commonly used to correct this problem.