Do orchids need UV light?

[spetrizio]

I agree, one webpage even if it is university page is not enough that you can be sure about something.

Also I agree that a large portion of IR light is not good for the plants.

I just want to say that 0% of IR light is maybe also not OK.

[littlefrog]

I have been told, although I have no real desire to find out for sure, that cannabis makes more THC with the addition of UV light. That is the only crop I've ever heard of as 'needing' UV. But I haven't really researched it.

I would predict that plants which grow in full sun would have some mechanism of using or at least reacting to UV light. Plants which evolve in lower light, under the shade canopy in the rain forest, for example, would not see nearly as much UV, and therefore I would predict would have less use for it. Since almost all of our orchids are growing a bit lower in the canopy, I'd say almost all orchids would not care about UV. Just a prediction. But if rupiculous laelias, which grow in full sun, require or respond to UV light, this makes perfect sense. A mottled leaf paph, not so much.

[naoki]

For the culture of orchids, I don't think UV is required. But in one sense, UV is "required" for some orchids in the nature. Most of you may not care about the biology of orchids, but just for your info.

Eyes of some insects (e.g. bees) are sensitive to UV unlike human eyes. So the flowers (common among yellow flowers) may contain carotenoids which reflect UV lights. And the flower pattern invisible to human may be important for the reproductive success of plants by guiding the pollinators to land on the correct location. With these plants, you can see the dramatically different patterns of flower under UV.

Far red light could be important in physiology of many plants. For example, phytochrome is involved in many important functions. It takes two forms (Pf and Pfr), and it changes between the two forms when the molecule gets hit by red light (660nm) or far-red light (730nm). So the plants can guess about the quality of the light by the ratio of the two forms. Phytochrome is also used to measure the length of night (long dark period will gradually convert Pfr to Pr). Then this information can be used to guess the seasonality (e.g. spring time etc). Some orchids probably shows photoperiodism, i.e., the day (night) length influence the initiation of flowering. For example, chrysanthemums and poinsettia are examples of short-day plants (the plant flowers when night becomes longer than a certain critical length). So it is possible that far red light could influence the flowering in some plants. But I don't think night length is a good flowering cue for plants from near the equator.

[DavidCampen]

I see that some people believe that UV helps algae to grow.
See page 6 here:
http://www.atlantalightbulbs.com/lib...rium-Lamps.pdf
"Daylight Star" fluorescent lamp with "UV Stop" -
"Reduces algae growth through a special UV-STOP protective sleeve"

They show that it cuts off light below 400 nm.