I have a 1000w grow light that is switchable between High Pressure Sodium and Metal Halide. In your book, Easy Marijuana Gardening, you suggest using HPS. However, some articles suggest using MH. Still others suggest using HPS and MH at different times during the grow cycle. Do you still stand by your statement?
State College, Pennsylvania

Yes. Using Metal Halide (MH) lamps in any stage of growing is a waste of time and money. More total light useable by the plant is produced by High Pressure Sodium (HPS) than MH lamps, so plants grow faster using HPS lamps alone.

When HPS and MH laps are lined up in rows in a grow room, you can see the “wave effect.” The plants under the MH lamps do not grow or weigh as much as the plants under the HPS lamp.

No formal studies have been performed to see if different visible light spectrums affect taste or potency, but anecdotal evidence suggests that it doesn’t.

The only reason to use an MH lamp rather than a HPS is to avoid the suspicion that a weird-colored light may arouse.

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