Lighting needs

In a single-light garden is it better to use an enhanced spectrum High Pressure Sodium lamp, like a Son Agro 430 watt bulb as opposed to a regular HPS, to emit more light in the blue spectrum?
The grow shop I go to still insists I need a separate Metal Halide for the vegetative stage.

C Walsh,
Amityville, New York

You definitely don’t need a Metal Halide (MH) lamp. They don’t produce as much total light or as much light in the spectrums the plants use. Plants grow perfectly well and faster under High Pressure Sodium (HPS) lamps than they do under MH. Tell the clerk in the garden shop you don’t need the MH lamp, just the HPS.

I don’t think the plants need the extra blue light offered by the Son Agro. Although plants use blue light for photosynthesis, they use red light more. In rooms with mixed lights MH and HPS, the plants between the two lights which were receiving a mixture didn’t perform quite as well as the plants directly under the HPS lamps, but slightly better than those under the MH. This leads me to think that higher blue light levels don’t necessarily lead to greater production.

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