Grow lights, difference between Halogen and Metal Halide?

[Suzy]

1. What is the difference between Halogen and metal halide lights?
2. For a six plant garden, wouldn't 1000 watts be excessive?

[Rob]

1. Tungsten Halogen lamps are as inefficient to operate as incandescence and are very expensive to operate. Their
lumen-per-watt output is very low.
2. 400 watt metal halide or high pressure sodium is good for 2 to 6 ft. square area and they last longer too.