Contrast between an object and its background is especially and critically important for visual tasks that require discrimination of shape and contour. An obvious example of this need for contrast, is a printed page where doc letters can be best read when printed on a lot of lot piece of paper. For same tasks requiring discrimination of surface texture and detail, less contrast between the surface and its background is desirable, because our laws adjust automatically to the average brightness of a scene. Someone's seen against a brightly illuminated background would be silhouetted it would be difficult to discern that person's facial features. The surface brightness of a task area should always be the same as its background or just a little bit brighter and maximum brightness ratio of three to one between the top surface and the background is generally recommended. Between the task area and the darkest part of the surrounding room, the brightness ratio should not exceed five to one.

Higher brightness ratios can lead to glare and associated problems of 50 and loss of visual performance.