Too much fluorescent light?
 

I have a T5HO setup and I try to give my orchids as much light as possible--but I do understand light duration can affect blooming for orchids.

There are a couple of questions which I was wondering and would like to discuss with some veterans here (some are stupid questions :blushing:):

1) What actually "burns" an orchid? Is it UV and heat? or some sort of photo-stress? If it's UV and heat, does that mean fluorescent light (if not touching orchids or in high heat) don't really burn orchids?

2) Is there a photo-stress in general for too much light? (aside from UV and heat stress)

3) Subtle purple pigmentation (expression of anthocyanin) has been a good indicator for some orchids that they have received optimum light. I have also read that growing orchids to the point that they are very purple is desirable and actually blooms orchid better.

Is there a concern of too much anthocyanin on leaves?

Moderator: Please feel free to move my thread if I should discuss this somewhere else.

Thanks!

I don't think UV is too much of a problem, but burning can be from direct heating, or from excessive heating of the plant tissues by exposure to to much light intensity. Leaf tissue can only dissipate the heat at a certain rate, so if the temperature and light intensity together are greater than what can be dumped, it's "scorch city!"

Some plants simply won't bloom well if exposed to too much light. Some of the best phalaenopsis plants I have ever seen were grown in almost complete darkness in an algae covered greenhouse.

I'm agreeing with Ray on the scientific portions. Speaking to growing Phals under lights, it's surprising how little they need to grow/bloom/etc. I'm sure there is optimal and suboptimal, but so long as they aren't burning, it's probably enough to get to see blooms. I grow mine on the lower side of the recommended FC scale, and they seem to do just fine, so I rarely get to see evidence of the anthocyanins "sunscreen". Also, I would guess that some Phals can't produce this effect, as I've had several novelties suffer burning without any indication of leaf pigmentation.

As a side note some species are particularly persnickety about how much light they need.

Thanks for the reply Ray,

I think I noticed stunted leaf span on a phal. and on my B. cucullata from very high light (don't have enough experience in growing to confirm that). If my observation is correct than perhaps the phals you saw have larger leaves from less than optimal light which equals to more storage to compensate (or actually more beneficial) for high photosynthetic rate in higher light?

If that is true, perhaps we should exploit growing larger and longer leaves by using less than optimal light during leaf development period and then move them into very high light? :biggrin::biggrin:

I had a B. nodosa about 2 feet away from the light but was turning very purple (about 1000fc for 14 hours). I guess my original post is more of a question for catts/brassavolas...do I

a) maintain subtle pigmentation and know that they are receiving optimal light or

b) Push the limit and turn it into a purple Barney

I was also curious if too much anthocyanin would actually result in lower photosynthetic rate.

---------- Post added at 03:31 PM ---------- Previous post was at 03:21 PM ----------


Did this happen under a fluorescent light?

I would think that any orchid will go straight to 'burn' if they're chucked under higher light without adaptation. The way I understand it the pigmentation is an effect of prolonged high light exposure, yet still below the 'burn' threshold.

For me a small amount of coloring indicates that the light levels are good. When I first got lights for the Phals they were getting really very purple after a few weeks, so I reduced the number of hours of light (since raising the lights was not an option). You don't want the plants to be entirely purple, light stress isn't good for them either.

Some of mine were probably too rapid high light issues, but most were larger plants just growing north too close to the light.

Hi You have got somenice comment above but I Would like to some comments...

Heat and UV "burn" orchids in different way, heat cook or boil them, and the UV-light detroys the pigment by radiation. The anthocyanin is a way to prevent damage of radiation, but is triggered by increased light fluxes in general. I would say that UV is never a problem with T5HO setup!


YES, there are numerous of scientific study where plants are stressed by high light fluxes from "normal" wavelengths.


I would not say 'optimum' light but 'enough' light. Optimum light has to my knowledge never been investigated for orchids in a scientific way. This may be semantics but as is said above, some orchids do better in lower light that do not trigger anthocyanin production. This depends on the species and some supposed "low light" species can be grown in VERY bright conditions if the get acclimatized during long time.



In general I have found myself that a instant increase in light levels triggers anthocyanin production but after a while the plants acclimatize and the anthocyanin go away. A further increase, and this observation repeat itself until the limit where the orchid can not longer adapt.

/M

---------- Post added at 11:57 AM ---------- Previous post was at 11:54 AM ----------

Oh, the sign of radiation damage is bleching of the green color. You get white to pale yellow spots and areas where the radiation has damage the light absorbing pigments in the leaf.

Thanks for clearing that up! I was confused by what I read on "burning" your plants under fluorescent light if you don't acclimatize it; since there is no UV, heat is not really a big issue either and is not something you can acclimatize to.

Thanks, found some literature on photoinhibition on orchids and plants. I know understand that anthocyanin is not only protecting your orchid from UV but also absorbs visible light wavelength (especially blue) to protect your plants from photoinhibition.

Thank you very much for the tips and detailed explanation. These cues will be extremely helpful!

Thank you all for your time to write the replies, I really appreciate it!

No problem

I just relized that I made a little error . Heat can be deliverd in two ways, convection and radiation. But heat radiation do not bleach pigments.
It is the high energy photons in short wavelenghts (blue to UV) that bleach...

You can burn the Phal pretty easily, but burning the B. cucullata is pretty hard to do.

Wow, that is some intense light!! Now I see why you were worried about the cucullata! lol

Alan Koch of Gold Country Orchids talked about this. He said that too much light can inhibit flowering, however when I grew my plants in Hawaii, many of them were in full sun all day and flowered very profusely. I think it really depends on the species.