LED vs. HPS: Truth about photosynthetic eff. & uniformity

[whazzup]

An interesting metric I came up with the other day that uses data from this thread is what I called reflector 'photosynthetic radiation efficiency.' This provides the relative percentage of PAR range umol/s that exit the reflector as compared to the PAR range umol/s that is emitted by the lamp.

Just divide the reflector's umol/s per joule in PAR range by the lamp's umol/s per joule in PAR range, and multiply by 100. The lamp's total output is often reported by the manufacturer, as total PPF, or PPF per watt.

I was a bit surprised to learn, for example, Gavita PRO DE 1000W HPS reflector has a photosynthetic radiation efficiency of about 81%, that is, about 19% of radiant PPF emitted by the lamp is absorbed by the reflector/fixture.
https://www.icmag.com/ic/showpost.php?p=6738657&postcount=6837

It is an interesting measurement, but quite incorrect. What you are referring to is the light output ratio, also called LOR. The 81% is not correct. Send the fixture to a professional lighting company which has a large scale photogoniometer to get the correct results, instead of trying to integrate points on a grid. In fact it is a lot more, but you just can not measure that accurately with an integrated point measurement. Which btw is also discussed in the same paper.

It is interesting that you came across LOR "the other day" because that is what professional lighting companies work with and specify all day long. It shows how uninformed you are, and I see you are quoting every time from the same documents and source. As a scientist you should know that you can not rely on a single source.

LOR is the basis of reflector ratings as in efficiency. Then we haven really talked about spread and uniformity yet, or exit angle of the reflector, or light losses to the ceiling with open reflectors. We haven't talked about how the lamp temperature can influence the lamp voltage and the output of a lamp, and we certainly have not discussed yet why you should change your lamp at 4% depreciation, and not ten, because you are not growing tomatoes in a greenhouse but silver on a stick in a climate room. You have a lot still to learn.

 

[Beta Test Team]

An interesting metric I came up with the other day that uses data from this thread is what I called reflector 'photosynthetic radiation efficiency.' This provides the relative percentage of PAR range umol/s that exit the reflector as compared to the PAR range umol/s that is emitted by the lamp.

Just divide the reflector's umol/s per joule in PAR range by the lamp's umol/s per joule in PAR range, and multiply by 100. The lamp's total output is often reported by the manufacturer, as total PPF, or PPF per watt.

I was a bit surprised to learn, for example, Gavita PRO DE 1000W HPS reflector has a photosynthetic radiation efficiency of about 81%, that is, about 19% of radiant PPF emitted by the lamp is absorbed by the reflector/fixture.
https://www.icmag.com/ic/showpost.ph...postcount=6837

It is an interesting measurement, but quite incorrect. What you are referring to is the light output ratio, also called LOR. The 81% is not correct. Send the fixture to a professional lighting company which has a large scale photogoniometer to get the correct results, instead of trying to integrate points on a grid. In fact it is a lot more, but you just can not measure that accurately with an integrated point measurement. Which btw is also discussed in the same paper.

The values are correct, they were measured by a 3rd party accredited lab using NIST certified integrating sphere (for lamp AND fixture irradiance measurements, separately) and the most current protocols. They were not created by "points on a grid."

Just because the values are not what you want to see doesn't mean they're not correct. You have serious biases, which is to be expected, as Gavita is your employer. But that doesn't mean what you're writing is accurate, in fact, it has been proven otherwise (see this thread).

If you have provable data (facts) to refute what I claimed, and can provide their source (not just the values), please post them.

And no, a photogoniometer is not better than using an integrating sphere to calculate that value.

It is interesting that you came across LOR "the other day" because that is what professional lighting companies work with and specify all day long. It shows how uninformed you are, and I see you are quoting every time from the same documents and source. As a scientist you should know that you can not rely on a single source.

I didn't "come across LOR the other day," because I thought it up the other day all by my lonesome. I never claimed it was a unique idea. And I have never heard of LOR until your post; I'm a scientist, not a light fixture manufacture.

The 81% value I listed is correct, no mater how much you want it not to be so. Unless you have facts, i.e. data, you can post to refute the claim.

The facts stand for themselves, see the data in this thread, or just use your biases and tell me I'm wrong.

LOR is the basis of reflector ratings as in efficiency. Then we haven really talked about spread and uniformity yet, or exit angle of the reflector, or light losses to the ceiling with open reflectors. We haven't talked about how the lamp temperature can influence the lamp voltage and the output of a lamp, and we certainly have not discussed yet why you should change your lamp at 4% depreciation, and not ten, because you are not growing tomatoes in a greenhouse but silver on a stick in a climate room.

And do you know why? Because most of those things are off topic. And yet, uniformity was already discussed, and it's been proven Gavita is lacking in uniformity.

Also, relamping at 4% deprecation sure sound like $$$ to your ears, doesn't it? You talk about photosynthetic efficiency as if it's the most important factor, and then suggest relamping like every 8,000 hours?! Okay, sure. For a large operation with thousands of lamps relamping that often is a financial non-starter.
http://www.lighting.philips.com/mai...pressure-sodium/horti/928196305116_EU/product

To those reading, relamping at 90% (i.e. 10%) is fine, especially when a quantum sensor is used to ensure correct irradiance.

You have a lot still to learn.

Look, you're mad that the facts don't equal Gavita's claims and marketing, I understand. But for a company and human (you) that doesn't even know what PPFD means, I think you're a pot calling the kettle black, my friend.

 

[OIBI]

Hey OIBI, aside from the comapny I already listed, I have spoken with a different company about testing luminaire efficiency as defined in this thread (using NIST cert. method). Their rate is about $285 per luminaire, for 360-830 nm waveband range. Spectral units from the integrating sphere can be radiometric, as milliwatt/nm, which can be converted into quantum units (umol/s/nm) easily, then PAR range values can be integrated to find photosynthetic umol/s per joule.

The company is ITL, Inc., out of Colorado.

Personally I think every luminare manufacture should have their units tested in this way, especially LED and LES luminaries, and share those data with their customers.

I'll have to make a few basic builds to send in for testing. I'd be very interested to see what the CXB series is capable of.

 

[morgandecaptain]

Basing anything off the LEDs listed in the start of this thread is a waste of time,try looking at the newer high efficiency LED tech out there,those lights are mediocre at best.

 

[Sativied]

Hate to bump an old thread but since Bibled thumpers keep presenting this thread to me while making a crucifix with their fingers...

And do you know why? Because most of those things are off topic.

No, when you start a discussion with in the title "the truth about photosynthetic efficiency & uniformity" those things are not off topic.

Your 81% is about efficiency at the source and like par w efficiency does not equate to photosynthetic efficiency directly. Nope, does not. That mixup is a common mistake made in the led community, just like thinking using led equates to better uniformity. Plants are not a flat surface without reflective walls around it and par watt efficiency is not the only factor of light fixture that affects photosynthetic efficiency, something that occurs in leaves, not in a reflector, light, nor on paper.

The goal of a grow light reflector is not maximum reflector efficiency. It's as the title of the subject says, about photosynthetic efficiency. That's why you put a light above your plants. Not to achieve theoretical efficiency numbers at the source, but for photosynthesis in the plants.

Directional light is suboptimal for photosynthesis. LED being directional is often presented as an advantage, as in you don't have to direct light away from the plants. The "truth" is, it forces the light mostly down, instead of more horizontal. The light inside the beam is not uniform either. Lenses can help, some use reflectors, but those also reduce efficiency 10-15% (according to ledil).

LED arrays with many diodes spread out over a surface turn that negative into a positive, uniform spread of the emitters instead of trying to emit uniformly from a single or low number of light sources. This trick to make up for it being so directional is partly negated by using a low number of the highest output cobs.

Uniformity is in this context how uniform the light is spread throughout the crop. Worst case scenario is light merely straight from the top. Heating up (if at all) and possible saturation and photoinhibition at the top layer of the canopy. Inherently not providing adequate penetration (hence intra/inter lighting in pro settings). Scattered light, penetrating the crop from many different angles, including reflecting more throughout and by the plants itself is what leads to the best uniformity of chlorophyll levels and photosynthetic efficiency throughout the plant. It makes a significant difference with directional light, up to negating that reflector loss %, but in real world photosynthesis.

See page 16 and 28 of plant light basics and application, hernandez, uni of arizona, for mere examples, or google the widely spread research about diffuse glazing for greenhouse and why exactly that works so much better.

Once the cxb or similar becomes large enough to use only one it may not be a bad idea to point it upwards into a reflector or point one at a diffusing wall insteading of ignoring the advantage(s) of a reflector to claim high par w efficiency and pretend that equates to more photosynthesis efficiency... the latter depends on additional variables using a particular light results in, how a reflector delivers the light and how a light influences leaf temp throughout the crop.

TLDR: Par watt efficiency does not equate to photosynthetic efficiency, especially when comparing completely different light sources.

 

[timmur]

Hate to bump an old thread but since Bibled thumpers keep presenting this thread to me while making a crucifix with their fingers...


No, when you start a discussion with in the title "the truth about photosynthetic efficiency & uniformity" those things are not off topic.

Your 81% is about efficiency at the source and like par w efficiency does not equate to photosynthetic efficiency directly. Nope, does not. That mixup is a common mistake made in the led community, just like thinking using led equates to better uniformity. Plants are not a flat surface without reflective walls around it and par watt efficiency is not the only factor of light fixture that affects photosynthetic efficiency, something that occurs in leaves, not in a reflector, light, nor on paper.

The goal of a grow light reflector is not maximum reflector efficiency. It's as the title of the subject says, about photosynthetic efficiency. That's why you put a light above your plants. Not to achieve theoretical efficiency numbers at the source, but for photosynthesis in the plants.

Directional light is suboptimal for photosynthesis. LED being directional is often presented as an advantage, as in you don't have to direct light away from the plants. The "truth" is, it forces the light mostly down, instead of more horizontal. The light inside the beam is not uniform either. Lenses can help, some use reflectors, but those also reduce efficiency 10-15% (according to ledil).

LED arrays with many diodes spread out over a surface turn that negative into a positive, uniform spread of the emitters instead of trying to emit uniformly from a single or low number of light sources. This trick to make up for it being so directional is partly negated by using a low number of the highest output cobs.

Uniformity is in this context how uniform the light is spread throughout the crop. Worst case scenario is light merely straight from the top. Heating up (if at all) and possible saturation and photoinhibition at the top layer of the canopy. Inherently not providing adequate penetration (hence intra/inter lighting in pro settings). Scattered light, penetrating the crop from many different angles, including reflecting more throughout and by the plants itself is what leads to the best uniformity of chlorophyll levels and photosynthetic efficiency throughout the plant. It makes a significant difference with directional light, up to negating that reflector loss %, but in real world photosynthesis.

See page 16 and 28 of plant light basics and application, hernandez, uni of arizona, for mere examples, or google the widely spread research about diffuse glazing for greenhouse and why exactly that works so much better.

Once the cxb or similar becomes large enough to use only one it may not be a bad idea to point it upwards into a reflector or point one at a diffusing wall insteading of ignoring the advantage(s) of a reflector to claim high par w efficiency and pretend that equates to more photosynthesis efficiency... the latter depends on additional variables using a particular light results in, how a reflector delivers the light and how a light influences leaf temp throughout the crop.

TLDR: Par watt efficiency does not equate to photosynthetic efficiency, especially when comparing completely different light sources.

Yep and it is one of the reasons why I like Cycloptics Greenbeams. With that said, some of the DYI COBs have amazing spectrum, but they are too directional for my taste. Have you seen Suncloak? "They really capitalize on your point: LED arrays with many diodes spread out over a surface turn that negative into a positive, uniform spread of the emitters instead of trying to emit uniformly from a single or low number of light sources". Interesting approach with a mostly vertical canopy. Their yield per square foot of area is pretty high due to this.

Of course they chose to emulate HPS spectrum which makes sense if you believe that DE HPS kicks ass because of, not in spite of, it's spectrum!

 

[Sativied]

Both look interesting, the Cycloptic greenbeam and the Suncloak too... Though yes that color is... weird. It's a form of intercrop lighting, phillips has modules for it too, but then used horizontally. The density of fixtures in that suncloak example is high though, but the same concept. I think that works better in larger setups or at least larger plants, with a little more working space..

I'm not directly suggesting to spread out the light at the source more, the part you quoted, it helps, but on a plane not necessarily a plant. In the suncloak they don't just spread out the source over many points from the top, they went a step further towards the most extreme scenario where a dynamic grid positions and rotates leds towards the optimal position based on a real time inverse raytrace simulation - or simply put putting the leds around the plant.

What most called side lighting basically starts to make a lot more sense when using led. It's a pretty big thing in horticulture, top lighting vs intra and interlighting.

I think there's a simpler solution, even when using cobs, and that's also turning the negative of being directional into a positive. People often assume directing all light towards the plant instead of a reflector is the big advantage, and without much consideration take the shortest path between the light and the plant and point them straight down. While pointing them with an angle more than a few degrees could have a huge impact on uniformity in the way that matters. It would still require planning a fairly evenly spread on the horizontal plane but most to avoid extremes, hotspots. And of course reflective material on walls allows for additional options.

Point every cob to the opposite end of a tent would be a crude example.

Or perhaps a heavily scattering lens...