The quantity of light emitted by lamps ismeasured in lumens. By way of reference, a100-watt incandescent lamp emits about 1750lumens. While the quantity of light producedby a lamp is measured in lumens, the purposeof all lighting is to produce illumination (i.e., toprovide light on a surface). The intensity ofillumination is measured in footcandles. Afootcandle is the illumination produced by onelumen distributed over a 1-square-foot area.For most home and office work, 30 to 50footcandles of illumination is sufficient. Fordetailed work, 200 footcandles of illuminationor more allows more accuracy and lesseyestrain. For simply finding one’s way aroundat night, 5 to 20 footcandles may be sufficient.