Fluorex flood light

That's a 65W CFL. Yes, it has a pretty good reflector, but CFLs are good for about 70 lumens/watt, so it will have an output of at most 4550 lumens, while a decent 4' 54W T5HO will put out 8% more lumens with 17% less power consumption - AND, being linear, will light that shelf more uniformly down its entire length. I would also bet that the bulb supplied is NOT a plant light bulb, so is likely very high in the blue and especially green (that part of the spectrum the human eye is most sensitive to), with very little in the red

Orchid Karma's comment looks like a question, not a statement of fact, and in fact, it sounds like it isn't necessarily considering complete info.:

In the first place, fluorescent bulbs are not black-body radiators, and the color temperature is a "corrected" or "correlated" color temperature (CCT) , intended to "look like" - again to the human eye - a black body spectrum, not match it.

Secondly, while a 4400°K black body radiator does have its peak output at the 660 nm absorption peak, in the case of a 6500°K radiator (that of the sun plus the blue back-scatter of a clear sky at noon in the summer), the energy intensity at the 660 nm wavelength is actually 5x that of the 4400°K source, and the blue - also important for chlorophyll absorption - is more than 10x that:



I look at it this way: our plants have evolved and grown under the 6500°K light source, a plant light of that color temperature - even if "correlated" - is likely to match that best, so why fight it?

 

I haven't seen a convincing evidence that orchids require red light to flower. I think the red light stuff is for photoperiodic plants.

But the effect of light spectrum to the shape of plants could be more interesting aspect. Generally, blue light can reduce the leaf expansion (make the plants more compact). Although I haven't seen scientific experiments on orchids, this seems to be fairly general among plants. (let me know if I'm wrong). But I won't be surprised that orchids could have different response, too. With florescent light, I've been using 5000-6500k most of the time. But with white LEDs, I'm mostly using 2700-3000k. Both seems to work OK. The higher K bulbs look brighter to human eyes, so I wonder this is the reason why most people use these.

I think, in LED, warmer white has a slightly higher usable energy (for photosynthesis) per photon, but cooler white can emit more photons per watt of electricity. With florescent light, I believe most of them are triphosphor based, so there are usually only 3 main sharp peaks in the emission. So it is slightly different situation.

As Ray said, linear florescent (T8, T5 or T5HO) is better than CFL since you have 48" length.

 

I think you missed part of my point, Steve. The 2700° lamp is NOT what the plant needs for the red end - in fact it has far less red than the 4400° bulb.

Color temperature is a way to express and entire spectrum, not a specific wavelength.

Yes, a 6500° plant light bulb is better than a 5000° one, if you interpret "matching sunlight" to be better.

 

Hmm, Ray. I'm not following you here. Here is an comparison of 2700k vs 6500k emission spectra of florescent light
2700K

6500k


taken from (message #4 of another forum.

Different brands probably have some variation, but the height of the three major peaks seems to be the major difference between the different color temp bulbs in this case. So by looking at this, I'm guessing that 2700k has more photosynthetically usable photons (It is a bit difficult to interpret the figs because the y-axis is watt instead of photon flux).

Even though the absorption peak of chlorophyl may be around 680nm, when you look at the action spectra (more useful than absorption), actual peak is around 630-640nm for many species, I believe. Here is the related topic of conversion of PAR (photosynthetically active radiation) to Yield Photon Flux (YPF), which shows the peak to be around 625nm. So the peaks for the florescent light could be slightly lower than the peak for the action spectra, but it is probably still more useful for photosynthesis than blue.

 

Hi Naoki.- I guess I was thinking more of true blackbody radiators, but spectra I have seen for horticultural fluorescents (is that was those are?) looked more like the bottom plot, but with the red, blue, and yellow-green peaks to be more equal.

I know that there is some research going on in the "spectral balance" area at Philips and a few other places, but it seems to me that the lower spectrum, with the slightly more blue than red, more closely matches the relative intensities in natural light, so I'd feel more comfortable using those - even if I needed more wattage to get more photon flux.

I was communicating with a guy familiar with LED horticulture lighting (mostly used for supplemental-, rather than as primary or sole lighting, and he commented that white LEDs, having so much blue in their spectra, "would be perfect for lettuce". I have got to see if I can find some references, although we all know that there's likely nothing in any of them about orchids.

That YPF data appears to be nothing more than numbers associated with the known absorption spectrum. Am I missing something?

 

That may be a bit of an over-interpretation, Steve. It is known that chlorophyll has the most absorption at those two peaks, and while it would seem logical that those, therefore, will provide the highest rates of photosynthesis, we really don't know that. A photon is a photon, but those at the red end of the visible spectrum have a lot less energy than do those at the blue end, so what does that mean to the rate of photosynthesis? Also, the plant, as a whole, absorbs all wavelengths between rough 400 & 700 nm, and much of that is converted into energy that is "pumped" into the photosynthetic process, so they affect the rate of the reaction, as well.

I suppose we can surmise a bit from the natural growing conditions, too - vandas, growing in close to full sun, probably take advantage of the entire spectrum, while those that live in deep shade, may see less blue, as those shorter wavelengths just don't "bend" around the edges of leaves and branches like the long ones do, potentially leading to a shift in the arriving light spectrum - just guessing.

I've looked into wavelength and flowering, but all I can find is that "some" orchids respond to shortened day length. No kidding?

 

I don't know where the person got the spectra, but it seems to be from normal (i.e. not tuned for plants) florescent bulbs. The grolux type has much lower emission of yellow-green (like the ones which Polyantha of ST was using for his photosynthesis measurement).

You may be right, but as you know, the natural condition isn't the best condition for the cultivation. It will be interesting to see how the horticultural light research will make progress! Agruculture may have a different goal; they just want to maximize the yield per given energy. But we care about the entire life-cycle of orchids.

I would expected that warmer white is more ideal for lettuce. According to Fig. 7 & 8 of this poster, leaves become small with lots of blue. And you are right, orchids may be different from sunny crops.

This article which Bjorn posted to ST is good to explain the difference between absorption spectrum (p.5) and action spectrum (p.6). YPF is based on action spectrum, I believe. The two spectra are somewhat similar, but red is indeed more useful for photosynthesis. Action spectra incorporates both the absorption rate and the difference in the downstream photosynthetic reactions. So from the action spectrum, we do know that the best wavelength for photosynthesis is slightly lower than the absorption peak of chlorophyll. Blue light has higher energy, but it is not relevant for photosynthesis (DavidCampen corrected me about this point, and he is right after I checked a couple refs). Well, the punch line is that absorption spectra of chlorophylls doesn't tell the whole story.

However, the measurement of action spectra is almost always with high-light crop plants. As you inferred with the Vanda example, low light orchids may have different action spectra. Indeed, if you look at the original paper, which is cited in the heliospectra article, there are variation among species. The second issue is that the photosynthetic rates for action spectra is usually measured with monochromatic light. Sometimes there are interaction effects if you use multiple wavelengths. I don't know well about this interaction, but people frequently call it Emerson effect. Photosynthetic rate at 680nm + 700nm light is higher than the sum of the rate at 680nm alone and the rate at 700nm alone (I forgot the detail, but something like that).

Ray is right that there are some orchid species which shows facultative photoperiodism (meaning that the day lengths can HELP initiate flowers, but it is not the only cue, and it is not completely REQUIRED). The spectra is important for photoperiodic plants because the "eye" of plant (phytochrome) is sensitive to red and far red light. Actually, more recent research shows that phytochrome is a part of story how photoperiodic plants initiate flowers.

 

Steve, I'm not sure 6500K is more effective per watt (if you are talking about photosynthesis). Without the actual measurement (or published data), I'm hesitant to say, but 2700K etc seems to contain better spectrum (but overall output/watt may be lower, which I don't know). But the photosynthesis is a part of the story, so Ray feels better with 5000/6500k. If you want to have more efficient (and the cost is not an issue), you can get these bulbs tuned for plants. Take a look at this thread

 

Well, I (and lots of people) like to dig around this kind of things and discuss about details, but in practice, any bulbs seem to work reasonably well. So I'm guessing that you can use the bulbs which come with the fixture, and see how your plants grow.

 

So that makes me wonder if certain shifts the solar spectrum reaching the plant - traveling through a different "cut" of the atmosphere, depending upon the time of year - might play a role. If so, being able to manually affect that might allow one to get plants to bloom at exactly the right time for that show, rather than too early or late, as is the usual case!

 

It would seem to me that the origins of the species will give us some clues as to the "forcing" factors. Many phalaenopsis species, for example, are from equatorial regions of the world, where day length stays pretty constant, so that is not a trigger factor. The ones that are "strictly" equatorial tend to be the ones that bloom on and off throughout the year. Those species that are just outside those regions are the ones that are more likely to react to average temperature changes.

Consider this scenario:: Plants are happily growing on "cruise control" in warm, humid conditions, then a period of cooler conditions take over that result in a period of heavy rains. After those rains subside and the conditions warm up a bit would seem to be a likely time for insects (pollinators) to hatch and mature, so... The plants have "learned" that a period of decreased temperature is the signal that pollinators will be soon available.

Of course, being orchids (or anything natural, for that matter), there are exceptions, but that seems as likely as anything.

As you move farther from the equator, temperatures tend to fluctuate a bit more, so that is a less reliable indicator of what's coming up, and day length (or something associated with it) takes precedence.

Shifting gears entirely, I think that the response your miltonia (was it a miltoniopsis? They are the cooler growers.) was more likely a metabolic response. I'm really talking through my hat on this one, but I can picture the chemical processes of energy assimilation and fuel production as one side of the coin, with those related to the consumption of the fuel and subsequent growth and flowering being the other, and that the rates of those two processes are affected differently by temperature. Maybe it's something as simple as the warm conditions throwing off the optimum balance of the two, thereby not permitting the plant to have the "stores" necessary to bloom properly.