Excess of light without excess of heat
 

Hi,

What happens to orchids if they are exposed to an excess of light without an excess of heat?

Nowadays leds have become so efficient that you can easily provide an excess of light without having an excess of heat.

I have a mini growing tent (actually it is a stealth grow area within a small cupboard) in which I have a temperature between 26-28 degrees Celsius with lights ON and a temperature between 19-21 degrees Celsius with lights OFF.

When the lights are ON, the leaves have usually a temperature of about 1-degree Celsius higher than the temperature inside the cupboard (maybe the transpiration is not optimal as I read that the temperature of the leaves should be equal or lower than the ambient temperature? or maybe it is normal as my light has also infrared LEDs that provide some extra heat...).

Anyway, I am providing Phals with 200-250 PAR, Bulbs and Dendr with 300 PAR, and Cattleya with 400 PAR. Lights are ON for 14 hours x day. I understand that this is (significantly?) above optimal PAR and DLI for these orchids, right?

I have searched the web without finding any conclusive info about what happens to orchis exposed to an excess of light without an excess of heat.

Maybe somebody in this forum has some experience with that?

Thanks in advance.

Dav

I think you're pretty spot on with the PAR you're hitting the different species with. Temps look good too. As long as you are running decent humidity I wouldn't worry about your current conditions much.

This guide might be helpful

in my experience I have been shooting for a DLI of 4-6 for low light orchids, 6-10 for medium light orchids and 10-15 for high light orchids. as long as you aren't operating at extremely high temperatures and low humidity dont stress if you're giving them a bit more.

If the light levels are much greater than “a bit” more, you will likely burn them. Plus, depending upon the plant, it can screw up blooming.

Folks seem to be of the impression that more light = more blooms, but “it ain’t necessarily so”. There are a multitude of chemical processes that occur in a plant. Some are driven by light, and some are slowed by it (or precluded from happening because others interfere).

Each plant has its own “Goldilocks point” of conditions, and light is no exception.

Heat and Light are factors, which have little to do with each other.

Each plant accepts a temperature range, which can be surprisingly broad (check geographical distribution AND elevation range).

For plant growth, the 3 inter-related factors are

• Light
  
• Water
  
• Nutrients

While certain genera do require a true rest period, most orchids will happily keep growing - as long as a rest requirement is not triggered by outside factors (changes in light, temperature and/or water supply).

Hi all,

Many thanks for your replies.

Let me be a bit more specific.

Let's assume (it is just an invented assumption) that a Phal starts to get burned in nature when it gets a PAR of about 300 PAR units (I do not remember the definition of PAR unit by hard...) for 12 hours of exposition to the (filtered by the trees, etc...) sunlight.

But in nature, a PAR of 300 is accompanied also by a significant heat generated by the sun that is outside from the PAR freq. boundaries. And this is not the case with the Led lights that can instead provide only (or almost only) the frequencies within the PAR.

Now, if we remove the frequencies outside from the PAR boundaries (the one that the sun provides and that are responsible for a significant amount of heat) and we provide only the frequencies within the PAR (which is what led lights do in contraposition to the sunlight), then at what PAR would the Pahls start to get burned?

I would expect that the PAR required to burn the Phals under led light is significantly higher than the PAR required in nature (i.e. with the sunlight).

Does it make sense to you?

Thx.

Davide

Daily Light Integral (DLI) is what's important, and that's measured in moles of photons - where a mole is 6.023x10e26.

PAR is simply saying the plant is exposed to all photons between 400 and 700 nm wavelength. There is no "300 PAR". Saying a plant gets PAR would be roughly equivalent to saying it gets "temperature".

A plant in nature does not get uniform light all day long. It starts as a photon collection (µmol/square meter/second) of zero at sunrise, reaches a peak at noon, then drops back to zero at sunset, affected by whatever shading it may get from clouds, leaves, etc.

Sure there is some heating, but as I said before, the relative lack of heating from LEDs does not mean the plant can take a lot more light.

Thanks Ray. Basically you are saying that with less heat (i.e., due to frequencies outside the PAR interval) the plant can get a bit more light within the PAR region, but not much more. OK, got it.

Yes, of course, PAR without specifying the time exposure does not mean anything (that's why the assumption was considering as example a 12 hour exposure).

Dav

Actually, PAR is pretty meaningless...

"PAR" specifies a "color" - a range of wavelengths; nothing else - sort of a broader extension of "red" or "orange" or "yellow", "green", or "blue". It is just saying "all of the above", which constitute Photosynthetically Active Radiation - i.e., what the plant can use. It says absolutely nothing about what energy they are getting.

There's something about the temperature too. If the temperature isn't in some particular suitable range, then the photo-synthesis process won't happen ---- aside from having enough water and anything else it needs for that process.

Well, I forgot to mention another assumption I made, otherwise I agree that just knowing the PAR and the time of exposure (i.e., the DLI) is not enough to draw any conclusions on weather a plant is getting enough/good light.

I made the assumption that the good led lights available nowadays in the market (like the Viperspectra I am using) do have an optimal spectrum output. This means that within the PAR freq. boundaries, the spectrum is very similar to the spectrum of the sun (actually, these good light brands do pump a bit more the red frequencies w.r.t. spectrum of the sun, as this is proven to be very beneficial).

Now, if we know upfront that the light we are using has a good spectrum, then by adding the PAR level and the exposure time (i.e. the DLI), we have all what we need to know.

I will keep experimenting with (very) high DLI with some of my orchids (as below) and report here in the forum the results on monthly basis:
- Pahls: DLI of 12
- Bulb and Dendr: DLI of 15
- Cattleya: DLI of 22

And of course I will make sure that the temperature ranges and the humidity will also stay within the optimal values.

Cheers,
Davide

---------- Post added at 11:50 AM ---------- Previous post was at 11:26 AM ----------

Indeed, thanks for reminding that.

Dav

---------- Post added at 12:06 PM ---------- Previous post was at 11:50 AM ----------

Thanks for the link!

Dav

---------- Post added at 12:28 PM ---------- Previous post was at 12:06 PM ----------

I did the DLI calculation, I am significantly higher than what you are using...See one of my replies below.

Cheers,
Dav

In line with this conversation, and I don't mean to hack it, sorry!

Does light compensate temp?

For example, if we have low temps and good sun/lighting, does natural sunlight compensate the temperature?

For example; not gradually or constantly, let say the temp is 50-60º constantly but 2 days are cloudy and 3 days full sunlight

well, im no expert, but suusally if these are factors in a plants biology they have distinct sense and response, though of course both can influence the other.

perfect example is the strong daylight response of many deciduous trees, which require a certain number of photons to hit the leaves to maintain chlorophyll as a stable molecule (that’s the short version). when enough photons don’t hit them, the chlorophyll decays and we see fall colors (other molecules stored in leaf tissues). however, there is a lot that plays into this, such as amount of cloud cover, and evidence that temperature can affect plants in conjunction with light. a warm fall can drag this process out, or the trees will have a very hard transition into fall, but still drop their leaves. but it seems that if there is a strong response expression in a particular species to either temp, or light, then that stimulus is required, independently, to bring about the response. but of course there are ranges to the differences in these changes. what i mean is, if a plant is evolved to go dormant in the winter and shed its leaves using light as the trigger, then the plant would suffer/die if forced to maintain a set of leaves due to unchanging light levels yet still be triggered to dormancy by temperature. so temp and light, as some level, are intimately linked

With orchids, generalizing doesn't work... Orchids that come from more temperate zones (for instance Himalaya, northern India, southern China, more northern regions of southeast Asia) will experience distinct seasonal changes of temperature, day length, light as well as changes in rainfall (linked to light, when there are few clouds it's also brighter even with lower sun angle). Orchids that grow at tropical latitudes (near the equator) will experience much smaller variations in day length, but light may or may not be affected by rainfall patterns. And those from higher elevations will experience some seasonal temperature variation as well as diurnal temperature variation, that those at sea level won't. So a discussion needs to include information about "Which orchids?" to be useful.

In cultivation, we certainly modify the parameters that an orchid experiences in the wild, but even the most complex hybrid still goes back to species, with needs and conditions that need to be taken into account for successful growing.

Not sure if I got your question right. Do you ask, for instance, if an outdoor phals that typically requires a minimum air temperature of 18 degrees Celsius can do well in an air temperature of 16 degrees under the (filtered) sun light?

Well, I am also no expert, but I think that surely the sunlight can compensate (at least a bit) for that.

However, I think that this is not a common situation at all. Neither in nature nor under artificial lights. Unless you carry outside your orchids during daylight and bring them (quickly) back at sunset every day...

If the air is 16 degrees Celsius during daylight or when the artificial lights are ON, one can bet that during the night (or with lights OFF) the temperature would drop to an unbearable level.

Dav

Yeah, I mean just you said.

and, yes you're right, no matter what the night will be cooler ...every day.

Think of orchids as unique “Goldilocks”, particularly when it comes to temperatures and light levels.

IDEALLY, they do best within specific ranges of each. Yes, they may tolerate something a small degree outside of them, but they will not grow or bloom as well.

A deep understory plant that normally grows hot and with no direct sunlight, for example, will not do as well if grown cool, but with more light.

It’s all about chemical reactions occurring within the plant, and those chemical reactions are affected by temperature, light intensity, light & dark duration, to name but a few factors. Even the water supply affects it.

If there is plenty of water at the roots, hormone signals tell the stomata to open, allowing gas exchange to occur more freely, allowing carbon fixation to occur more rapidly. If the root system is dry, that doesn’t happen, as the plant goes into “conservation mode” to save water.

As Roberta said - each plant is unique, the needs are very specific (hence my “Goldilocks” comment), and the complexity of plant processes are too great to make any generalizations.