I recently had an email discussion with a customer about converting to LED lighting for plants on shelves, where the overhead space is limited, and that led me (no pun intended) back to a slightly modified design I used decades ago when mixing fluorescent shop lights and incandescent bulbs over my plants.
First, let me “step back” for a moment and state that in my experience, white LEDs, given the proper output, are quite acceptable for growing plants. I have used Cree outdoor floodlights over my plants when brought inside for winter since moving. The correlated color temperature (CCT) doesn’t seem to make much difference, although the “warmer” ones seem to generally give more lumens for the watt, but even at that, I lean toward lamps with higher color rendition indices (CRI), as that affects how they look compared to under natural sunlight; the sun’s CRI is 100 by definition.
Considering the space constraints of shelving units, specifically the distance from the lamps to the plants, floodlights are pretty much out of the question as the relatively narrow beams would lead to non-uniform lighting. However, standard LED light bulbs, intended for use in incandescent fixtures, are just about ideal!
To build such a light panel, you need plywood, some lamp holders, bulbs and wire, and simply mount the holders to the plywood similar to this (bottom and side views below):
When I built my version of this, I cut the female end off of an extension cord, and attached the leads to the last fixture, stripping the insulation off of the wires spaced to match the others, so that a single cord powered all of the lamps in parallel. Just be sure the cord can handle the current of the bulbs combined – a much easier task with LED’s!
Using my 8-bulb example above, and using Cree Soft White, 90+ CRI, “100 watt equivalent” light bulbs having a true current draw of 17 watts, the fixture would draw 136 watts total, meaning that a 20 amp cord should be adequate, and the lamp would put out 12,800 initial lumens, giving it almost a third more light output than two, 4-foot, 54 watt T5HO fluorescent lamps. Depending upon the plants grown and just how much “head space” you have, you may need to go with lower-wattage bulbs.
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