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Old December 31, 2013   #2
Hermitian
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Join Date: Dec 2011
Location: Vista, CA
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For ornamental indoor plants many types of supplemental "plant lights" will suffice. But for production of fruit much more energy in a specific spectral range is required. To produce a crop of tomatoes:
• Light source must have color temperature of 6500 Kelvin.
• Add up the total Watts of the light source. Use actual Watts, not Lumen equivalent.
• Light source must be directed downward by a reflective hood.
• Position the light source 1 meter above the floor and measure the projected area of the light.
• The total watts divided by the projected area must be in the range of 50-75 Watts per square foot.
• During use, keep the light source 1 meter above foliage.

This works out to about 18 4-foot T5 HO 6500K bulbs mounted above the plants in a 4'x4' grid. For cucurbits, you can get away with half of this.
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