Are they efficient at generating useful light for plant growth?
No, the best floro/hps/mh lighting each being approx 5X more efficient at plant growth than halogen. A good way to measure plant growth efficiency of different types of lighting is PAReff. PAR stands for Photosynthetic Active Radiation: the wavelength range of light between 400 and 700 nm that can be absorbed by leafs for plant photosynthesis. PAReff is the PAR/Watt efficiency ratio over a certain area. Some examples: Philips Advantage Fluorescent, 5000K: 1.44 PAReff Philips High Pressure Sodium deluxe: 1.38 PAReff Philips Dense-Line Emitter Metal Halide, 4100K: 1.38 PAReff Philips Spot Halogen Masterline, 2950K: 0.263 PAReff People usually choose halogen for the “low startup” costs of a halogen light. The real costs of halogens result from its low efficiency. 500 Watt halogen lighting produces about 0.08 Watt/s/nm in the green-yellow spectral region which is about the same as 80 watts of cfl’s. A 500w halogen grow will cost approx $63 for electricity, whereas a more efficient light so
