Conventional Grow Light Technology

High Intensity Discharge lamps - There are 3 broad categories of HID lamps: mercury vapor (MV), high pressure sodium (HPS), and metal halide (MH). MV lamps are the least efficient of the 3 groups, in which radiation from mercury produces the major portion of the light. Lamps in which radiation from sodium vapor produces the major portion of the light are referred to as HPS. And finally, lamps in which radiation from metal halides in combination with metallic vapors such as mercury produce the major portion of the light are referred to as MH lamps.

For an excellent discussion on HID lamps, the Department of Energy in 2004 produced a Technical Support Document: Energy Efficiency Program for Commercial and Industrial Equipment: High-Intensity Discharge Lamps, Analysis of Potential Energy Savings (Docket #: EE-DET-03-001) that can be downloaded HERE.