From BlenderWiki

Lights Common Options

Here are some options available for all types of lamps.

Dist

The Dist field indicates the number of Blender Units (BU) at which the intensity of the current light source will be half of its Intensity. Objects less than the number of BU away from the lamp will get more light, while objects further away will receive less light. Certain settings and lamp falloff types affect how the Dist field is interpreted, meaning that it will not always react the same, see the page about light falloff.

Energy

The Intensity of the light sources illumination (from 0.0 to 10.0).

Color

The color of the light sources illumination.