05-10-2011, 09:09 AM
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Chasing Crickets
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Join Date: Jan 2011
Posts: 57
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With regard to the questions people had about night-time lighting for plants: Many, if not most, flowering plants (i.e., NOT ferns, mosses, Selaginella) in the temperate zone use the length of day to help time certain of their life-cycle events, such as when to germinate, when to leaf out, when to make flowers, and when to shed leaves. So how does a plant know how long the days are? In bright light, a certain pigment is converted rapidly from form A to form B. In darkness or dim light form B gradually decays back to form A. Some part of the plant's metabolism is sensitive to the concentration of form B, which sets off a chain of chemical reactions that result in a growth response. Pretty neat, huh?
Growers who want to manipulate the time of flowering, so as to have Poinsetta's or Christmas cactus looking pretty for Christmas, do so by regulating the lighting periods the plants are exposed to.
Some plants are quite sensitive, so that just a brief flash of light at night will convert pigment A to B, and the drift back to A will have to start over again. However, most plants rely on a combination of environmental cues, including temperature and moisture level, to time their major seasonal activities. A little bit of light at night doesn't have much, if any, effect on them. If this weren't so, plants growing near city lights would get all out of whack. (Actually, this does happen sometimes. When I was in grad school there was a dogwood tree that was very close to a campus light that was on all night, and it always lost it leaves later than other dogwoods that were further away.)
Tropical plants, however, live where there is little difference in day length in the course of the year, and they rely less heavily on day length for timing their events. In the rainforest one encounters trees of the same species in the same forest blooming at very different times of the year. In fact, I have even seen different parts of the crown of a single tree blooming or flushing out new leaves at different times.
I don't know how orchids, tillandsias and bromeliads are effected by photoperiod, but I would guess that for popular terrarium species the effect of a little light at night would be negligible. Since there are so many websites devoted to these plants, it probably wouldn't be hard to find out.
I hope this helps.
Martin
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I do agree with Martin, the light from your LEDs is unlikely to have any effect on your plants -- especially with their being underwater to boot.
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