Lumens

Lumens is simply a measurement of light; it takes into consideration the human eye sensitivity curve so that more properties is given to the yellow-green part of the light spectrum.

The lumen (symbol represented: lm) is the International System of Units of luminous flux, which is the measure of the perceived power of light to the naked eye. Luminous flux is much different than the radiant flux which is the measure of the total power of light emitted from the light bulb, in that lumens are adjusted to show the varying sensitivity of the human naked eye to different wavelengths of light.

For example standard 120 V, 60 watt incandescent light bulb emits 600-800 lumens, but a simliar 13 watt compact fluorescent lamp emits the same amount of lumens.