T5 lighting spectrums

[ma_sha1]

I noticed that my orchids seems to be a bit slow on bud development unto full bloom, so I decided to done some analysis of the bulb spectrums

[ma_sha1]

6500k Spectralux bulb


3000K bloom bulb


Natural sun light


HID lamp


I was surprised to see that my t5 set set up does not provide the 660nm deep red, even the 3000k bulb doesn't have it.

My conclusion: 3000k t5 is NOT optimal for blooming, it works, just not that great.




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[ma_sha1]

Next, I evaluated a T5 bulb with 650/660 peak


Aqua life 650 nm Roseate pink bulb


I now run a combined 3 bulb set-up


The combined spectrum give me the needed 660 mm for blooming:


The combined looks of Kevin, the color & tint is similar to before when I had 6500kx2 + 3000k+1


Conclusion:
I believe it's necessary to blend a specialized T5 with 650nm into typical T5 set ups. Even 4x3000K T5 won't give you that.


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[naoki]

Pretty cool that you have an access to spectroradiometer. What kind is it?

Is there a strong evidence that 660nm is "required" for orchid blooming? I assume that you are talking about phytochrome-mediated photoperiodism. I see a couple Phalaenopsis, but I haven't seen strong evidence that they are sensitive to photoperiod. There are some orchids which are photoperiodic, though. If you are interested, Joseph Arditti's book: Fundamentals of Orchid Biology has a table of how flower induction occurs for many orchid species (p.209-212).

[ma_sha1]

It's a hand held spectrometer MK350 I borrowed from work.

I am not worried about photoperiod, I
am trying to address the intensity at the right wavelength issue.

660nm is not "required", if you look at chlorophyll a adsorption spectrum below, The peak red light adsorption is close to 660. It can absorb 610 nm as well but at greatly reduced efficiency, ~10x less efficient.

Add 660 light mix into T5 lighting allows it to mimic sunlight better in terms of providing optimal lighting for chlorophyll A.

I follow the general orchid light recommendation for my paph & phal. I.e., I provide 1000-1500 foot candles of intensity under T5, the amount of 660 light is easily 10x less than if I put it under natural sunlight at same intensity.

It's much better now since I supplemented 660nm
I also found out during my search for 660nm T5, all the cheap bulbs are missing 660 regardless of Kelvin. 6500k or 3000k or 4000 k, doesn't matter. Expensive bulbs doesn't mean it'll have 660 either, you'll have to search for the spectrum spec from the bulb to know for sure.





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[naoki]

Originally Posted by ma_sha1

It's a hand held spectrometer MK350 I borrowed from work.

That is very cool! I wish there were cheaper specs. I have made a practically free specs from DVD-R, but it is a bit too touchy for me.

Originally Posted by ma_sha1

660nm is not "required", if you look at chlorophyll a adsorption spectrum below, The peak red light adsorption is close to 660. It can absorb 610 nm as well but at greatly reduced efficiency, ~10x less efficient.

I see, but as you said it is just an absorption spectrum, which is a part of photosynthesis. Photosynthesis "action" spectrum is more informative. Take a look at Figure 1b of this poster:

http://cpl.usu.edu/files/publication...b__2576523.pdf

So to gauge the usefulness of different light source for photosynthesis, people compares PPFD (photosynthetic photon flux density of PAR (photosynthetically active radiation). From your spec data, you can calculate this quantity. But since you have spec. data, you could also calculate YPFD (yield photon flux density) by weighing the spec data by the action spectrum. There is a brief explanation of this in the poster.

Originally Posted by ma_sha1

I follow the general orchid light recommendation for my paph & phal. I.e., I provide 1000-1500 foot candles of intensity under T5, the amount of 660 light is easily 10x less than if I put it under natural sunlight at same intensity.

Under the constant light and different spectrum from sun, you might be giving more than needed for paphs. There is a paper which measured the photosynthesis of a paph species, and the photo saturation point was around 100-200 micromol/m^2/s. I can try to locate the paper if you are interested in it.

Originally Posted by ma_sha1

I also found out during my search for 660nm T5, all the cheap bulbs are missing 660 regardless of Kelvin. 6500k or 3000k or 4000 k, doesn't matter. Expensive bulbs doesn't mean it'll have 660 either, you'll have to search for the spectrum spec from the bulb to know for sure.

That's right, frequently, different K of fluorescent bulbs are just different composition of phosphors. So the emission peaks are same, but their relative intensities differ. So this does influence the YPF, though.

[ma_sha1]

I like the technical discussion, we do measure lux & calculate ppfd in some of the work projects as well. However, I don't feel that it's necessary in a beginners orchid board discussion.

Good point about sun's intensity. Even in my west window, I measured afternoon sun light on my orchid at ~35,000 lux but I only get it for 3-4 hours, which is roughly equal to 15 hours of artificial light at 9333 lux.

Therefore, I think the general recomendation of light intensity of 9,000 -15,000 lux is pretty good & I can move my orchid between these two locations without stree them out. The only real difference is the reduced spectrum quality when moved under T5, thus, my recommendation of supplementing the 660 peak. With the addition of 660 bulb, we can make t5 lighting close to natural sun light in lux as well as quality for photosynthesis.

[naoki]

I'm not quite following your logic here, sorry... Are you saying that the total amount of light (called Daily Light Integral) from 35000 lux (=3252fc) at 3-4 hours is the best for all orchids? Or are you simply saying that in your situation, constant 9333lux at 15 hours can give the same DLI as your window? In either case, it doesn't sound like a general recommendation for other people.

DLI is a useful idea, but the plant physiology is a bit too simplified in this idea (especially for the shade plants like orchid). If the photosynthetic rate saturate at 200 micromol/m^2/s (= 1000fc=10760lux in case of sun), daily photosynthetic rate from your west facing window is much lower than under the weaker and constant artificial light. This is because during the brief, intense light period, the plants can't utilize all of the light because the intensity is beyond the maximum possible photosynthetic rate for the plant (beyond the saturation point).

Also why is it important to make the emission spectrum of the T5 light close to sun light? If you are concerned about the efficiency (photosynthetic rate per given electricity watt), using the purplish plant bulbs which reduce the green peak should have a higher efficiency.

So the conclusion that the special plant bulb is "required" is rather missleading to beginners. I do agree that plant bulbs can achieve higher PAR efficiency (I've measured PPFD, too). 660nm peak isn't anything special. If you look at the action spectrum of photosynthesis, the actual peak is lower than the absorption peak of chlorophyll. From your data, there is a peak around 610nm even for the 3000K or 6500K bulb, which is within the range of the maximum photosynthesis.

This is a bit advanced, but it is a bit related to what you said. There is some scientific evidence that plants do need to acclimate from the natural pattern of sun light to the constant light. Many plants have tuned their machinery to have gradual increase in the intensity in the morning. So initially when you move plants from greenhouse to artificial light, plants can experience a "shock". But after a while, plants do eventually get accustomed to the constant artificial light.

[ma_sha1]

I never said 660 nm is required, because 610 is used just not as efficient. I think it's better if the 660nm peak is supplemented into T5. Which is kind if obvious to me in looking at the spectrums.

Feel free to disagree, but my interest is simply not strong enough to dig further into adsorption vs. action spectrum, no offense intended.




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