Yeah, this thread has really helped clarify some things for me as well. Thanks all! The distinction that PAR, itself, is not the measurement is lacking in many sources (or is very subtle and easily missed/confused). This whole thread is a pretty great discussion. I hadn't even considered the watts versus number of photons side of things.
LED lights and PAR w/ Paphs&Phrags
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Yeah, this thread has really helped clarify some things for me as well. Thanks all! The distinction that PAR, itself, is not the measurement is lacking in many sources (or is very subtle and easily missed/confused). This whole thread is a pretty great discussion. I hadn't even considered the watts versus number of photons side of things.
naoki
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Terry, I think one of the papers you are talking about is this (from the previous discussion):
Brodersen, C. R., Vogelmann, T. C., Williams, W. E., & Gorton, H. L. (2008). A new paradigm in leaf‐level photosynthesis: direct and diffuse lights are not equal. Plant, cell & environment, 31(1), 159-164. (link)
We have to be careful about how to interpret the results. This paper showed that at the leaf level, when the light is hitting the leaf perpendicularly, photosynthetic (PS) rate can be higher. The possible reason is that the penetration of the light to the deeper layers. There are several layers of cells in a leaf, and a layer with something called pallisade parenchyma cells is the most relevant for PS (in non C4 plant). This layer in leaves which acclimated to intense light become thick. Even within an individual, they can develop these different leaves (i.e. the part exposed to strong light develops "sun leaves", but shady part remains "shade leaves"). When there is a thick layer of pallisade parenchyma, the light hitting at an angle can't reach to the deepest cells. Therefore, the perpendicular light is better for PS. The difference was very small (10-15%). But when they tested with the shade leaves of the same species, the advantage is not observed. This is a a side note, but the same logic apply to explain why green light can enhance the overall PS rate in some situations (under intense light) since it can penetrate into the deeper region.
But you should be aware that at a plant (or community) level, there are data showing advantage of diffused light (cited in the paper). This is probably obvious; leaves are not always perpendicular to the light, so with diffused light, some light is going to hit the leaf at 90 degree angle, penetrating deeper. More importantly, with diffused light, you can avoid the shading effect (the leaves closer to the light source can shade the lower leaves). These are the reasons, that both in greenhouse and with artificial light, diffused light gives better growth. This is one of the reasons I now prefer linear modules (or pannels) of mid-power LEDs over COB although in a reflective grow tent, the point source light like COB LEDs can produce somewhat diffused light.
Brodersen, C. R., Vogelmann, T. C., Williams, W. E., & Gorton, H. L. (2008). A new paradigm in leaf‐level photosynthesis: direct and diffuse lights are not equal. Plant, cell & environment, 31(1), 159-164. (link)
We have to be careful about how to interpret the results. This paper showed that at the leaf level, when the light is hitting the leaf perpendicularly, photosynthetic (PS) rate can be higher. The possible reason is that the penetration of the light to the deeper layers. There are several layers of cells in a leaf, and a layer with something called pallisade parenchyma cells is the most relevant for PS (in non C4 plant). This layer in leaves which acclimated to intense light become thick. Even within an individual, they can develop these different leaves (i.e. the part exposed to strong light develops "sun leaves", but shady part remains "shade leaves"). When there is a thick layer of pallisade parenchyma, the light hitting at an angle can't reach to the deepest cells. Therefore, the perpendicular light is better for PS. The difference was very small (10-15%). But when they tested with the shade leaves of the same species, the advantage is not observed. This is a a side note, but the same logic apply to explain why green light can enhance the overall PS rate in some situations (under intense light) since it can penetrate into the deeper region.
But you should be aware that at a plant (or community) level, there are data showing advantage of diffused light (cited in the paper). This is probably obvious; leaves are not always perpendicular to the light, so with diffused light, some light is going to hit the leaf at 90 degree angle, penetrating deeper. More importantly, with diffused light, you can avoid the shading effect (the leaves closer to the light source can shade the lower leaves). These are the reasons, that both in greenhouse and with artificial light, diffused light gives better growth. This is one of the reasons I now prefer linear modules (or pannels) of mid-power LEDs over COB although in a reflective grow tent, the point source light like COB LEDs can produce somewhat diffused light.
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Naoki, I can believe that diffuse light has some advantages and I think that was one of the papers I had found. My LED experiment began because I had hit the maximum electricity load my plant room could handle using fluorescent fixtures and the heat produced by my lights was not compatable with needed temperature drops for blooming. I also wanted more head room over plants to accommodate bloom spikes and wanted to be able to grow higher light plants. LEDs have given me all of that. If I were to go to diffuse LED lighting, I think I would be losing more light out into non-growth areas of the room and I am again about at the maximum for electricity drain, so want as much of the photons going to the plants as possible. Thus, more focused light is a benefit for me. I am working on a plan to run more electricity to the room. Then maybe I could experiment with some more diffuse light sources.
When I spoke to the seller about the lights, he mentioned that there is research that these (Aeon 60 degree T-8) lights actually penetrate the top leaves to also give light to lower leaves they are shading. Much of this discussion is way over my head from a technical standpoint, but what I can say is how well they grow phals, paphs and catts using the PAR readings you mention for each type (as measured at top of leaf canopy on the Quantum PAR meter you use). Many of my plants show the purple shading/spotting of maximum light levels on their leaves. Especially the phals and catts with thicker leaves.
naoki
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Yes, minimizing spill-over at the edges of the grow area does influence the "effective efficacy" a little bit. Some people do use a narrow beam angle at the margin of the grow area, and wider angles in the middle. But it won't work too well with a relatively narrow/small area.
Sounds like that you might get better benefits from higher efficacy LEDs. There is a huge difference in efficacy among LEDs. The better one can give around 2.7 micromol/J while many of them are around 1.2 micromol/J (just slightly above T8, which is around 0.8-0.9 miromol/J). So you can get the same amount of light with a half of the total electricity consumption.
The best way - from the plants' perspective (literally & figuratively) - to achieve quality lighting is to provide multiple light emitters spread out over a broad area from high up, so you get the maximum "spread" to the light. Adding lighting that is at angles off of vertical at the perimeter also helps, as does having white walls.
Yes, that means more wattage, but you have to weigh your priorities.
Yes, that means more wattage, but you have to weigh your priorities.
masaccio
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terryros, I'm in the process of doing a track light install with the ALT MR16s. Since they're LEDs, I was assuming they are low voltage, but (DUH) since you can use them in standard household screw-in fixtures, they're regular 120 volt. Is that right? Thanks!
My electricity knowledge is weak, but my 40 degree angle MR16 bulbs from ALT are 7 watts by specifications. They work in standard track lighting fixtures. I currently have about 30 of these bulbs. I use them up high over Phals, Phrags, Paphs, and Miltoniopsis so they accommodate almost all spikes.
masaccio
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Ha! Mine too. Jerry just got back to me as well, and confirmed this. Thanks for the quick response.
Do you need them to be low volatge? Most LEDs I have seen are advertised as low wattage. If it screws into a normal household fixture, it will be using 120 V (or has internal circuitry to convert from 120 V AC > 12 V DC). However, if it is low wattage then it will be pulling less current (since wattage is voltage * amperage). That's my understanding at least.
My ALT 4’ tube LEDs use 42 watts each. I have 3 tube fixtures made for LEDs (from same company as tubes) as ballast is different, as I understand it. (Frankly, I am way out of my league here, just repeating what I was told when I bought them re ballast). Here are the specs re Watts/volts/etc. on each tube’s sticker:
T8 tube V4 IP 68
Power consumption: 42 W
Input: AC 100V to 277V ~ 50/60 Hz
80-330 mA
Not suitable for dimming
Hope this adds clarity.
A couple of years ago, Orchids Ltd. set me up with MR16 V6 72 degree bulbs for my orchids. Shelving was 30” apart, and 36” wide. The height worked for all orchids but for my Phrag. Sorcerer’s Apprentice.
For high-light orchids, I used 2 bulbs; lower light, one bulb. They recommended one bulb above Phrags.
After being underwhelmed by the results for my Phrags, I noticed on their website that they no longer sell that particular bulb, but now sell a “stronger” one. Once I added 2 bulbs, fairly evenly spaced above my Phrags, things really took off.
Some of us are just learning about LED lighting through trial and error. At least, I am.
For high-light orchids, I used 2 bulbs; lower light, one bulb. They recommended one bulb above Phrags.
After being underwhelmed by the results for my Phrags, I noticed on their website that they no longer sell that particular bulb, but now sell a “stronger” one. Once I added 2 bulbs, fairly evenly spaced above my Phrags, things really took off.
Some of us are just learning about LED lighting through trial and error. At least, I am.
If lamp makers would 1) Provide their lamps' output in terms of photon flux (µmol/sec) and provide intensity maps (see blow), then it would be easy!
I agree, Ray. Debra and I had to do that mapping manually with our bulbs and that is only the start. Then you have to figure out the correct LED light intensity for each type of orchid. Almost all of the published literature with photon flux and daily light integral requirements of various orchid types was done with natural light, almost always in a greenhouse setting. At least with the LED bulbs I have used, I can get acceptable growth and blooming with light intensity and daily light integrals that are less than published numbers. It has taken me years of fiddling to start to get closer to optimum in terms of light intensity and that is probably only for my particular environment and cultural conditions!
masaccio
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My initial response to this is, "Kill Me Now." I've mentioned that I'm working with Orchids Limited for a couple of long and narrow setups. I bought a few of the 7-watt MR16s at 720 lumens each (they're around 5000k). There is an online chart that recommends these bulbs for medium-high light orchids (which to me translates as cattleya light) at a distance of 3 feet. So at a distance of 32" my meter is measuring UNDER 30 PPFD directly under the bulb. At about 15" it measures around 60. Does it seem reasonable to anyone that these bulbs are suitable for "medium-high" light orchids??
masaccio
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Yes, I'm just learning myself. Although I think the correct phrase for me is that I'm NOT learning, or that's how it feels anyway! Oh, wait. You meant a 720 LUMEN bulb, right? I haven't seen a "72 degree" bulb. You probably have a 40 degree bulb that is supposed to cover medium high light orchids within a 32 inch space at 3 feet overhead. At any rate, experience is gold. Would you provide a little more detail about the specific plants you're growing in the setup you described? When you say "high light" orchids, which specific ones are you referring to? Thank you!
I need 200-400 micromoles/m2/sec peak photon intensity at the top of Cattleya leaves to get good growth and blooming. You cannot get that with the MR16 bulbs at 3 feet! At the height were the intensity is high enough, you are not very high over the plants and the foot print is not very wide. I only use the 7 watt MR16 for lower light orchids where 50-80 micromoles/m2/sec gets the job done. For Cattleyas I am using 60 degree 15 or 20 watt ALT bulbs at 6-12 inch heights depending on which bulb to get the 200-400 intensity. I would not try and do Cattleyas with the MR16, 7 watt bulbs.
The beam angle is 72 degrees; that is what is meant by the specification.
When Orchids Limited said to me “high light” orchids, they included Catts in that category.
What I’ve got under the 2-bulb, 36”- wide, 30” - high shelf: Phrags: Frank Smith; Cardinale; Magdalene Rose; Eumelia Arias; Elizabeth Castle; Betheva; After-Glo; NoID Besseae hybrid; Schroederae; Green Hornet; Eric Young. I also have a couple of Disas there, but I’m thinking they could be a bit closer to the bulbs, so will raise them up a bit. This is my first foray with Disas, though, so I’m not absolutely sure. The orchids on this shelf sit at an east-facing window, FYI.
So, for lower light orchids, if you had the MR16, 7-watt, bulbs at 36” height, which orchids might you expect to grow and bloom well?
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I don't think you'd grow and bloom very much well with those tiny lamps at that height. Masaccio's measurement was "under 30" micromoles/sq. m/sec. Multiply by 5 to get a gross estimation of footcandles - not much does all that well under <150 fc.
That said, I am surprised that Terry gets good cattleya growth and flowering at only 200-400 micromoles/sq. m/sec. Full sun is about 2000.
That said, I am surprised that Terry gets good cattleya growth and flowering at only 200-400 micromoles/sq. m/sec. Full sun is about 2000.
