Slight visual deficiencies can no longer be tolerated because of eye strain and fatigue. Optical correction with glasses has become necessary. The human eye has been forced into a condition of constant compensation for the varying focuses and light levels of modern life. The use of Vita-Lite fluorescents, which simulate the ultraviolet and visible spectrum of natural light, eliminates the eye's need to adapt to a new color of light as one goes from outdoors to indoors, reducing eye strain and fatigue in the performance of a difficult seeing task. Such eye strain and fatigue are experienced commonly with cool white fluorescent lamps.
Old eyes require a greater quantity of light than young eyes do for the same task.
Age and the difficulty of the task must be factored into the lighting practice for a particular space. Minimum glare should be the first consideration in the selection and placement of lamps and fixtures. Glare is any brightness that causes discomfort or interference with vision, resulting in ey-strain and fatigue. But the eye is a living organ and is much more complex than the most sophisticated camera. Both camera and eye have a lens, which focuses an inverted image on a light-sensitive surface.