Long ago our ancestors lived in unity with nature. They started work when the sun came up in the morning and ceased their labours when it set in the evening. Even today we retain some traces of the old cycle. That is to say, we move more alertly and can concentrate better in a brightly-lit environment. As a result, our work efficiency increases. In contrast, in a dimly lit setting our muscles respond more slowly and our capabilities decrease in general. Thus, to ensure top work efficiency the environment should be brightly lit. Fluorescent illumination, which produces light that is quite similar to sunlight, is a good choice.