Using Incandescent Grow Bulbs on Orchids to Supplement Natural Sunlight

by Lori W.
(Shawnee, KS)

This year, the large trees in my back yard have too many leaves, and not enough sunlight shines through two of my east windows on some of my Phalaenopsis orchids.

I just set up four full-spectrum incandescent 60 watt grow bulbs at the back of the third row of orchids to supplement the natural sunlight. I cannot use fluorescent lights because I have no place to hang the lights, and some of the orchids' spikes are two feet tall.

How far away from the orchids' leaves should I place the grow bulbs to keep the bulbs from burning my plants? How many hours should I have the grow lights on each day?

Most of the orchids on this third row are growing over the sides of their pots, and the undersides of their leaves are facing the grow bulbs. Will the undersides of the orchid leaves absorb light from the grow bulbs or just the top sides of the leaves?

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As long as the lights are a foot from the plant's leaves, they should be safe from burning. The problem is that the further away the light is, the less benefit the plant receives from the supplemental illumination.

The plant itself will indicate to you when it is getting too much or too little light.

If the growing area is too dim, the leaves will become a deep, healthy-looking green. This is desirable in other house plants but not in orchids. If the light is too bright, the leaves will begin to turn yellow.

Leave the lights burning for 14-16 hours per day during daylight hours. The orchids need a nightly rest period. You can use a timer to turn the lights on and off for you.

An orchid grown in just the right amount of light will display firm, light green leaves.

Plant leaves can absorb moisture and nutrients through the stomata on their undersides but I have never heard of a plant absorbing light through the undersides of its leaves. I don't think this is possible but I invite anyone with concrete knowledge of this aspect of botany to comment and enlighten us both.

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Jun 29, 2011
Incandescent Grow Lights
by: Cable Thompson

Incandescent lights are very energy-inefficient, so they mostly produce heat rather than light; make sure that they are far enough away from the orchids to avoid overheating them! Fortunately, Phalaenopsis are warm-growing orchids, so you don't need to worry too much as long as the temperatures aren't going into the 90's Fahrenheit (above 32C).

They also don't need very much light as orchids go; an east- or west-facing window is enough if it's not too shaded by trees and such.

You would probably have better luck with compact fluorescent bulbs (the 60W equivalents would work fine) as they are much more energy efficient, so you can get them closer to the plants without burning them. I suggest going with a color temperature as close to natural sunlight (6500K) as possible; "cool white" is better than "warm white", but if there's a "daylight" option available go with that.

I have an orchid care website, so you might want to check out my tips on growing orchids under lights for more information on the sorts of lights that work well for orchids, as well as my Phalaenopsis orchid care instructions.

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