The eyes are designed to be stimulated by light and to control the amount of light entering the eyeball. There are, however, conditions which exist today that are foreign to the natural lighting environment and can cause an adverse reaction to light. The largest single factor in the workplace is glare.

There are two general categories of glare: discomfort glare and reflective glare. I will discuss discomfort glare because it is the more common cause for light sensitivity. Discomfort glare is largely caused by large differences in brightness in the field of view. It is much more desirable to eliminate bright sources of light from the field of view and strive to obtain a relatively even distribution of light. You might be at greater risk to experience discomfort glare when the source of glare is brighter and when it is closer to the point of attention.

One of the primary reasons discomfort glare is a problem for computer users is that light often leaves the overhead fluorescent fixture in a wide angle, resulting in light directly entering your eyes. It is very common for the brightness of the fixture to be more than 100 times greater than that of the display screen that you are viewing. This is a particular problem of computer workers because they are looking horizontally in the room (assuming the screen is at ‘eye level’). Bright open windows pose the same risks as overhead light fixtures.

You are also at risk for discomfort glare if you use a dark background display screen- resulting in a greater brightness disparity between the task and other objects in the room. Other sources of large brightness disparity at the computer workstation include white paper on the desk, light colored desk surfaces, desk lamps directed toward the eyes, or which illuminate the desk area too highly. It is best if you keep all of the immediately surrounding illuminations around the screen approximately equal.