Metal Halide

Here is how the following recommendation was arrived at by Lite Manufacturing for metal halide 1000 watt lights.

Q: How much Light [for growing plants] do I need?

A: 20-40 watts per sq. ft. is a general guideline. The more efficient the Light source, the less watts per sq. ft. needed. For example using 1-1000 watt metal halide light, in a 50 sq. ft. area would give you 20 watts per sq. ft. and a total of 120,000 lumens.

Solving the equation given in the following link for "CU" or the coefficient of utilization of light, we get: Cu = (E*S*W) / (L*LLF) = (4760Lux * 50sq.ft. * .0929sq.meter/sq.ft) / (120,000lumens * .8) = .23 or 23% efficient. In other words we need at least 23% efficient reflector to direct the light to this 50 sq. ft. area to get our minimum 4760 Lux amount of light to grow plants for 12 hrs/day.

Now what about the electrical efficiency of the 1000 watts converted to 120,000 lumens. Recall that: One Lumen (at 5,550 Angstroms) = .00147 Watts. Actual light energy in wattage = 120,000lumen * .00147watts / lumen = 176 watt of light from a 1000 watts consumed. The difference is emitted as heat. Thus the electrical Light efficiency = 176watt/1000watt =.176 or 17.6% efficiency.

Summary: This setup converts 17.6% of it's energy to light of which 23% will need to fall within the 50 Sq. ft. to make plants grow.

Offered by Mike.