LED lights and PAR w/ Paphs&Phrags

[xiphius]

Another look at the units:

PAR (Photosynthetically Active Radiation) - Those wavelengths between 400 & 700 nm. There is no information on the actual spectrum or the amount of light being projected.

PPF (Photosynthetic Photon Flux) - How much light (number of photons) is leaving the source per unit time. It is a constant (ignoring lamp degradation).

PPFD (Photosynthetic Photon Flux Density) tells us the number of photons per unit time hitting a unit of area. Because photons spread out as they leave a light source, this is dependent on distance from the lamp, and is closest to lumens or lux, albeit plant-centric rather than human eye-centric.

(Theoretically, if all of the photons were collimated, with no losses to the sides, the PPFD would be independent of distance - think of a lamp made up of an assortment of lasers having PAR wavelengths, all pointing at your plant, or 100% of the output of a LED panel "piped" to your plants through optical waveguides.)

Thanks Ray! Yeah, this discussion has really helped clarify some things for me. I think this brief, basic, discussion of units and metrics is sorely lacking in many of the sources that try and explain PAR/PPFD online (even the most basic ones that try and explain things from the ground up).

 

[xiphius]

Thanks, but with one more tube and some CO2 it looked even better:

Very nice!

Yeah, one day I will take the plunge and set up a pressurized CO2 system. I have dabbled with DIY CO2 systems before, but they are usually a pain to maintain and keep consistent, so lately I have just gone the "low tech" route (easier to keep stable imo).

 

[masaccio]

Really appreciate all the information. Over the last few days I’ve slowly been coming to the realization that I have way more lighting than I need. I’ll be able to get hard data when my PAR meter shows up, but I’m pretty confident that I’m growing paphs under dendrobium or cattleya light levels. I’m going to have to completely overhaul my setup to be able to hang the lights higher. What’s interesting is that while I noted that several burned (largely delenatii or its hybrids - I thought parvis would be less likely to burn?) 80% are doing really well. Maybe a few here or there that are a bit bleached out, but many have spiked. Watering a good bit, Humidity 50-70%, temp 55-70, and a ton of airflow. Maybe all that adds up to them tolerating more light than normal. I’ll post some pictures later. Have a good weekend everyone.

Since this thread has begun, I've run across some helpful articles by Eric Runkle. I found this one to be current, concise and interesting, which discusses simple technology for different types of white LEDs and includes graphs of wavelengths emitted along with a good discussion: https://gpnmag.com/article/white-leds-for-plant-applications/.
He has written other articles as well, which can be Googled. Also, I've had time to experiment with my line-up of 250 watt equivalent white LEDs that were stressing all of my plants. I hoped not to have to replace the bulbs due to over-brightness. I lifted them to approximately 24"-26" above the tops of plants, give or take depending on light preferences. The bonus is that coverage is more even. The PPFD readings have all come more into line with those of successful growers (who posted in this thread - thank you!). The footcandle readings are is still high, but shade-lovers are not showing stress. The second part of the fix was decreasing illumination to around 12 hours per day. All of this can be further fine-tuned over time, but the danger seems to be over. Plants are proceeding nicely, with zero symptoms of over-lighting. Everything feels more nicely balanced and flexible. A spiking miltoniopsis bought at a show two weeks ago has continued to develop a perfect long spike and buds are preparing to open without any signs of stress or drying. So, in summary, thanks to Mr. Runkle, I have a better understanding of what my LEDs are providing, and thanks to this thread I'm providing a nicer growing environment for all of my plants. I hope some of this feedback might be helpful. Thanks.

 

[masaccio]

I have grown and bloomed my Phrags successfully under LED lights for about 5 years. I don’t grow many Paphs. Of course I have been tweaking potting mix and nutrition over this period of time, but I have kept the PAR reading at 80-100 at the leaf tops. My LEDs have a focused light beam of 40 degrees and a little data suggests that this more vertical light reduces the required intensity needed for photosynthesis. My Phalaenopsis receive only about 50 with the same 40 degree bulbs while my Cattleyas are given between 250-400 (depending on the species) at the leaf tops using 60 degree angle focused bulbs.\

Thanks so much for your recommendation of these bulbs, and the detail you've given on how you use them. Just a quick follow-up question, if I may. Do the orchids under these bulbs receive any natural light, other than ambient room light? It seems that these bulbs would offer very little wavelength in the red-spectrum and just wondered if plants might be receiving this from another source. Thanks!

 

[terryros]

There is a window in my basement plant room, so some plants would get a little natural light but most would get none of it. I think that others have also found that natural white or true white LED bulbs must have sufficient red and blue spectrum because growth and blooming seems to be acceptable. The Apogee Quantum meter that I use cannot tell me how much of any part of the spectrum is being delivered, but it is supposed to tell me the micro moles/m2/sec being delivered within the 389-692 wavelength interval. Obviously, everything could be in the shorter wavelength area, but since things look "natural" color to my eye (and to photographs) under the lights, I don't think that can be the case.

 

[southernbelle]

Thanks so much for your recommendation of these bulbs, and the detail you've given on how you use them. Just a quick follow-up question, if I may. Do the orchids under these bulbs receive any natural light, other than ambient room light? It seems that these bulbs would offer very little wavelength in the red-spectrum and just wondered if plants might be receiving this from another source. Thanks!

I have the LED T-8 60 degree tube lights from Orchids Ltd and they are the spectrum of natural daylight 5,000 k. The spectrum is just beyond 390-700 wavelength, so balanced red and blue. My room has zero ambient light because of no windows. I use the same PAR as terry ros. 3 bulb fixture above catts and 1 above phals and paphs. Lights are about 20”-24” above canopy. These are high intensity, give great light, so nice headroom. No problem blooming catts, paphs or Phals. I just showed this Catt Dinard ‘Blue Heaven’ at the Va Orchid Soc Show and won second in class. The flower was 6.25” across with a 2.75” lip. Young plant so only one flower but it was spectacular.

 

[shade131]

First of all, this thread has managed to increase my knowledge LED lighting regarding orchid by an order of magnitude. So that's a win.

I'll keep updates coming, but for now I going with the old adage " as much light as the plants can handle without burning" while being careful to ease new plants into it. That winds up being a range of 120(maudiaes and mottled species)-300 (multis/parvis/phrags) PAR at the leaves. 90 degree angle lights. (still not clear on how beam angle relates to PAR?) Got a few in spike right now ( Paphs Berenice, Julius, delanatii and Hung Sheng Tango, and Phrag Eric Young) so if none of those blast, I'll know I'm at least close.

My hunch at present is that after raising the lights I'm still at the high end of the range for all of them. If I took away air flow or humidity or increased photo period, I bet some would burn, which is kind of a problem since it's winter and I'd like to increase the day length come summer. I'll have to do some research to figure out which of mine are sensitive to day length vis a vis flowering before deciding if it's worth the risk to increase the length of the day. The main thing I don't want to do is burn anymore leaves. Just ruins the look of the plants. I have a big P callosum that I scorched, and it'll be a couple of years before it'll replace all of the burned leaves.

-Brandon

 

[shade131]

I have the LED T-8 60 degree tube lights from Orchids Ltd and they are the spectrum of natural daylight 5,000 k. The spectrum is just beyond 390-700 wavelength, so balanced red and blue. My room has zero ambient light because of no windows. I use the same PAR as terry ros. 3 bulb fixture above catts and 1 above phals and paphs. Lights are about 20”-24” above canopy. These are high intensity, give great light, so nice headroom. No problem blooming catts, paphs or Phals. I just showed this Catt Dinard ‘Blue Heaven’ at the Va Orchid Soc Show and won second in class. The flower was 6.25” across with a 2.75” lip. Young plant so only one flower but it was spectacular.

Wow that is a stunning flower. Well done. How long will that bloom last?......I finally gave up on the few Cattleyas that I had after fighting a scale infestation for months, but man those flowers are hard to beat.

 

[masaccio]

There is a window in my basement plant room, so some plants would get a little natural light but most would get none of it. I think that others have also found that natural white or true white LED bulbs must have sufficient red and blue spectrum because growth and blooming seems to be acceptable. The Apogee Quantum meter that I use cannot tell me how much of any part of the spectrum is being delivered, but it is supposed to tell me the micro moles/m2/sec being delivered within the 389-692 wavelength interval. Obviously, everything could be in the shorter wavelength area, but since things look "natural" color to my eye (and to photographs) under the lights, I don't think that can be the case.

Thank you very much for responding. I'm planning a second setup with very little natural light. I wanted to try the these ALT bulbs that you've written about. Feeling good about this now.

 

[southernbelle]

Wow that is a stunning flower. Well done. How long will that bloom last?......I finally gave up on the few Cattleyas that I had after fighting a scale infestation for months, but man those flowers are hard to beat.

I fought scale that came in on 3 plants until I learned to spray 3 times in a row, 7-10 days apart. Scale gone. It opened 2/13 and is still in bloom. Last bloom was last Nov and lasted 3 weeks. Flower is getting nicer with each bloom, or could be that cooler winter temps of hi 72 low 63 allowed for more growth before opening.

 

[Ray]

(still not clear on how beam angle relates to PAR?)

It doesn't.

First of all, PAR is the wrong term. PAR simply means the light is between 400 & 700 nm wavelength. What you're trying to determine is the PPFD (photosynthetic photon flux density) - the volume of light in the PAR spectrum reaching your plants per unit time, expressed in µmoles-per-square meter-per-second.

The PPF - the flux or volume of photons leaving the light per unit time - might be the same for different beam angle bulbs, but those photons are "spread out" more with the larger beam angle, so there are fewer per unit area hitting the plant.

If one of the lamps illuminated a circle 2 feet in diameter (area = 3.14 square feet) at a certain height, and the other illuminated a circle 4 feet in diameter (area 12.57 square feet) from that same height, The PPFD of the broader-beamed lamp would be 1/4 of that for the narrower one because the area illuminated is 4x larger.

 

[southernbelle]

By the way, I was a bit off on the color spectrum I reported earlier for my T8 5,000 k LEDs. I remembered I had written the manufacturer and they sent me this graph. No problem blooming things with these lights.

 

[shade131]

Thanks for the clarification, Ray. Between what you wrote and what I found on wikipedia, it finally clicked - why conflating PAR and PPFD is misleading and causes confusion:

"The irradiance of PAR can be measured in energy units (Watts/m2), which is relevant in energy-balance considerations for photosynthetic organisms........However, photosynthesis is a quantum process and the chemical reactions of photosynthesis are more dependent on the number of photons than the energy contained in the photons. Therefore, plant biologists often quantify PAR using the number of photons in the 400-700 nm range received by a surface for a specified amount of time, or the Photosynthetic Photon Flux Density (PPFD)

Lightbulb! haha...

 

[masaccio]

I have the LED T-8 60 degree tube lights from Orchids Ltd and they are the spectrum of natural daylight 5,000 k. The spectrum is just beyond 390-700 wavelength, so balanced red and blue. My room has zero ambient light because of no windows. I use the same PAR as terry ros. 3 bulb fixture above catts and 1 above phals and paphs. Lights are about 20”-24” above canopy. These are high intensity, give great light, so nice headroom. No problem blooming catts, paphs or Phals. I just showed this Catt Dinard ‘Blue Heaven’ at the Va Orchid Soc Show and won second in class. The flower was 6.25” across with a 2.75” lip. Young plant so only one flower but it was spectacular.

Wow, Nice job on the Blue Heaven! I've felt "stuck" with spotlight type LEDs because I love the flexibility and I think they look kind've cool. But I'm becoming more tempted to try the tube lights, and they would be easier to set up in my second location. Thanks for the great info.

 

[Ray]

Thanks for the clarification, Ray. Between what you wrote and what I found on wikipedia, it finally clicked - why conflating PAR and PPFD is misleading and causes confusion:

"The irradiance of PAR can be measured in energy units (Watts/m2), which is relevant in energy-balance considerations for photosynthetic organisms........However, photosynthesis is a quantum process and the chemical reactions of photosynthesis are more dependent on the number of photons than the energy contained in the photons. Therefore, plant biologists often quantify PAR using the number of photons in the 400-700 nm range received by a surface for a specified amount of time, or the Photosynthetic Photon Flux Density (PPFD)

Lightbulb! haha...

Just don't think that the "watts" used in that definition has anything to do with the wattage of the lamp.

 

[naoki]

Just don't think that the "watts" used in that definition has anything to do with the wattage of the lamp.

Hmm, strictly, they are the same unit, so they can be comparable. For example when you calculate the efficiency of a lamp, you calculate the emitted energy in light (watts) against the input electricity energy (watts). So the unit of efficiency is %. High quality LEDs can achieve around 60% efficiency (40% of electric energy becomes heat). This is relevant when you are designing how to deal with the heat.

Note "efficiency" is different from "efficacy", efficacy is measured in terms of lumen/W or micromol/J (note W = J/s), not %. In other words, with efficacy, you are comparing non-equivalent quantities.

In terms of photosynthesis, photosynthetic photon (or quantum) efficacy (PPE, measured in terms of micromol/J) is more important than efficiency by itself since it is mostly a quantum process as the Wikipedia quote mentions. Blue LEDs could have high efficiency, but in terms of PPE, red LEDs have a higher efficacy in general.

 

[Ray]

Naoki, while the watts may be the same unit, I think your explanation supports my contention that the watts of the lamp are not the "irradiance of PAR" watts hitting the plants.

 

[naoki]

Ray, you are correct; irradiance (in terms of W/m^2) is proportional to radiant flux (watt, the total light output from the bulb), which is the (lamp watt) * efficiency (%). So they are not the same, but there is a relationship between them (my only objection was "anything to do with" part).

Then irradiance measured in watts are not a good measurement in terms of photosynthesis.

People should be aware that so-called "spectrum plot" (spectral power distribution, SPD) is frequently expressed in terms of watts (as shown earlier in the thread). So you need to convert it to number of photons before you use it for photosynthetic purpose (illustrated in here). If you make the conversion, blue peaks becomes quite a bit smaller.

 

[terryros]

It doesn't.

First, I agree with Ray that what we are measuring with our Apogee quantum meters is peak photon flux density. Apogee reports the response of the meter for the PAR range of light frequency, which seems to imply that the meter is only/mostly measuring within this range. However, I see how it is possible that the meter is still measuring a wider range of frequencies.

Second, if I were home, I could give the several references that I found to research into the effect of collimated versus diffuse light of the same intensity on photosynthetic responses of plant leaves. The more collimated the light, the greater the photosynthetic response to the same photon density. This is the only explanation I have for why I can grow my Phals very well and to large size with excellent blooming with measured peak photon density of only about 50 at the top of the leaves using 40 degree beam angle lights. I get excellent results with Phrags at 60-80 peak photon density. These values are definitely lower than what has been obtained in greenhouse conditions with diffuse natural light. My Cattleyas are under 60 degree beam angle bulbs but I think this may still lower the required peak photon density compared to diffuse light.

 

[terryros]

Nuts, should have added that I think the collimated/vertical light effect may apply most to plants with mostly horizontal leaves, like many Phals. With my large flowered, unifoliate Cattleyas, the collimated light is probably passing somewhat parallel to many leaves, eliminating this effect. I think that is why I am finding that it takes 200-400 micromoles/m2/sec to get excellent growth and blooming, which is in agreement with the small amount of data published with natural light.