Incandescent lamps are, however, cheap and easy to work with. Most of the energy radiated by a fluorescent lamp, on the other hand, is emitted as visible light. This gives fluorescent lamps a relatively high efficacy and good color rendering properties. They have a long life compared to incandescent lamps but are more expensive and more complicated electronically. The light emitted by a more typical fluorescent tube consists of several prominent spectral lines.
Daylight consists of a much more even spread of wavelengths.
Lamp manufacturers often aim to make fluorescent lamps which reproduce this distribution in the energy they emit. In the following section we will look at some of the theory behind photometry. Radiant flux is usually measured in watts. Luminous flux is useful for describing the total light output of light sources. However, to describe the distribution of light from a source, luminous intensity is used.