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Light. Specifying and measuring it: NOT so easy. I call shenanigans

Thanks, the PDF is more readable. For anyone clicking on the link, it defaults to download rather than opening in a new tab, so you’ll need to open up the file after you’ve downloaded it.

Also, @theo it should let you upload images up to 10MB, and anything that is larger than the space of the post will create a thumbnail version that will expand when you click on it. If you’re having any issues with image uploads let me know and I can help get it sorted out.

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Great charts @Theo! What’s your thought on the spectrum argument though?

For comparison, here’s a few charts of the absorption spectra of the different pigments found in most plants:

Here’s a typical HPS emission spectrum:

@clones argument seems to be that you’re missing a huge portion of the chlorophyll/carotene spectrum, and putting in a lot of light in an unused section. What say you?


About your invitation, forgot about that:

Thanks but I don’t think you can afford me ;).

I would be happy already if you can provide me the PPF of your 400W fixtures equipped with Osram LEDs. We are very familiar with those LEDs, we use them as well.


17 posts were split to a new topic: Lighting questions for Theo

Well, the thing is, in horticultural research we already found out that photosynthesis is not so much influenced by spectrum directly. Of course there are minimum requirements to a spectrum and HPS is far from full. I refer to Bruce Bugbee’s experiment with different lightsources, from LPS to incandescent, and there was hardly any difference in photosynthesis. The big difference however is morphogenesis, which can result in gain on gain. So yes, you can grow a different plant under a wider spectrum light and it will stay a lot healthier under that light.

Of course we already know the beneficial effects of UV, and there is also a minimum of blue light you should have for a healthy crop. What if I were to say to you that I believe that in full spectrum high intensity light green light is more efficient than red and blue light?

There is still so much we don’t know, but we do know one thing: The spectrum of the sun never shifts. We know that we can manipulate a plant with different spectra. We can make it shorter with lots of blue light, and there is where LEDs come in handy, or make the plant stretch with just a little bit of far red light. We can make it more open with green light, and get better leaf positioning in a combination with blue.

It would be good to realize that the scientific community is still experimenting with light recipes for different crops, and we are very lucky that this industry is here solely by the virtue of a plant which in fact does quite well under this HPS spectrum.


Before we are going to discuss all lighting, let us stay on topic for a bit.

My point is: I take offense in how many LED manufacturers do their marketing and try to mislead the customer by not providing basic information.

I would very much like to see a situation such as in professional horticulture, where we do all share these specs.

I want to warn you against false information and misleading half-truths. I am not an LED hater, I just hate misleading marketing.


Is this the experiment you’re referring to? I found a couple different articles that hinted at a similar point though:

Very true, and given the fact that evolution produces some unusual adaptations, I wouldn’t be surprised if there was some benefit to a fuller set of wavelengths.

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Indeed it is. The other ones are interesting too btw. So much to read… I do about 5 of those papers each week…

Bugbee, B. 1994. Effects of radiation quality, intensity, and duration on photosynthesis and growth, p 39-50. In: T.W.Tibbitts (ed.). International Lighting in Controlled Environments Workshop, NASA-CP-95-3309.

I referred to it in my last Garden Culture article as well.


It might work the other way around as well: There are theories that 5 generations of plants, bred under HPS, adapt to the spectrum.


Those IR leds are for remote controls :wink:

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Can we get back on topic? Go find those LED specs…


A post was merged into an existing topic: Lighting questions for Theo (Gavita)

here is the thing. SWIM has been doing experiments with lighting for many years. CDM, LEP, LED, all kinds of HPS, side lighting, mixed lighting, all same conditions lo-fi extraction only in a controlled room which wasn’t actually that much of a stable temperature. With the same PPFD we did not get more yield of any technology. We got much more compact nugs with plasma, and better dry weight (didn’t look like much but exploded in your grinder!) and the 400V HPS performed outstanding every time. Nothing wrong with that. 600 grams per square meter in a lo-fi 1x1m tent was the average. That’s with 30% light losses in a square tent!

Grow style: Scrog, one plant per room, 70 litres gold label light mix, sannies tabs, bio-mineral grow with supplemental mycorrhiza and bacteria. Amnesia Haze - soma - selection from 200 plants.

SWIM’s work:


note the CDM Agro beginning of 2013…

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A post was merged into an existing topic: Lighting questions for Theo (Gavita)

Here are a few things to help out the conversation. @clones very good explanation on protons, you are correct. Since light has a electromagnetic wavelength aspect and a charged particle aspect there are more factors to consider. Since the wavelength is more condensed at the 440nm this is the primary photosynthetic response region that one may find HPS lacks. @Theo your four factors are very important, correct. Although there are other important factors like fixture price, DLI, heat output and AC needs, some LEDs are eligible for power company rebates, spectrum adjustment capability, and smartphone connectivity… moving into the future. I understand you are on the HID end and Craig is on the LED end. My only goal here is to educate and help you guys make the best informed decision to help the entire industry move forward… together.

DE Genesis 1000w HPS

Parameter Value
PPFD (400~700 nm) 579.55 μmol/㎡s
PPFD IR (701~780 nm) 69.471 μmol/㎡s
PPFD R (600~700 nm) 341.26 μmol/㎡s
PPFD G (500~599 nm) 214.95 μmol/㎡s
PPFD B (400~499 nm) 23.225 μmol/㎡s
PPFD UV (380~399 nm) 0.9934 μmol/㎡s
YPFD (400~700 nm) 243.48 μmol/㎡s
YPFD (380~780 nm) 243.92 μmol/㎡s
YPFD IR (701~780 nm) 0.0000 μmol/㎡s
YPFD R (600~700 nm) 160.85 μmol/㎡s
YPFD G (500~599 nm) 65.759 μmol/㎡s
YPFD B (400~499 nm) 16.809 μmol/㎡s
YPFD UV (380~399 nm) 0.4390 μmol/㎡s
R/ B 14.69
R/ FR 4.91
DLI 50.073 mol/㎡

38726 lux
λp (380~780 nm) 612 nm
λD (380~780 nm) 589 nm
CCT 1990 K
CRI 52

CLW Solarsystem 550

Parameter Value
PPFD (400~700 nm) 672.14 μmol/㎡s
PPFD IR (701~780 nm) 17.934 μmol/㎡s
PPFD R (600~700 nm) 483.24 μmol/㎡s
PPFD G (500~599 nm) 46.632 μmol/㎡s
PPFD B (400~499 nm) 142.34 μmol/㎡s
PPFD UV (380~399 nm) 0.5808 μmol/㎡s
YPFD (400~700 nm) 387.80 μmol/㎡s
YPFD (380~780 nm) 388.04 μmol/㎡s
YPFD IR (701~780 nm) 0.0000 μmol/㎡s
YPFD R (600~700 nm) 261.59 μmol/㎡s
YPFD G (500~599 nm) 13.965 μmol/㎡s
YPFD B (400~499 nm) 112.21 μmol/㎡s
YPFD UV (380~399 nm) 0.2362 μmol/㎡s
R/ B 3.39
R/ FR 26.95
DLI 58.073 mol/㎡

15573 lux
λp (380~780 nm) 647 nm
λD (380~780 nm) 0 nm
CCT 1792 K
CRI -5

This LED fixture draws 400w compared to a 1000w HPS

We are testing many different lights and running data in SPSS which you all will find helpful.
More coming this summer. Competition pushes price down towards cost.


This can be very frustrating! The way some LED companies choose to market their products. The goal of my Theses is to use business statistics to find the most economical lighting choice for a certain set of goals. Hope this stuff helps the conversation here guys.


You are measuring PPFD and YPFD, not PPF. So you can not compare that. Get an Ulbricht sphere and start integrating light instead of comparing a laserpointer to a flood light ;). Hold your PAR meter close to the LED on your phone and read the value, then start growing some plants with that. Please learn about PPF and PPFD because you are making the mistake that I am warning about: measuring PPFD at a distance. Also, you are still using for YPFD the McCree curve. You are considering a plant a leaf disk, not a system.

I’m not an HPS guy, I’m a lighting guy. We make LED fixtures too, just have not released them for horticulture yet. Really, I love LED, I just don;t like bullshit.

It may surprise you, but our customers are getting massive energy rebates on the 1000W DE fixtures as well. This is not unique for LED. HPS is, according to the EU electricity use standards, an A++ energy label technology.

Further more: labeling 380 nm as “UV” may be technically correct, but it is hardly UV. More blacklight. This term comes from aquatics fixtures that use “UV” to light up corals. LED fixtures that say they emit UV too, are all around that wavelength. However, there are a few fixtures that incorporate UV fluorescents. Thos emit real UV. UV LEDs are priceless. The cheap plastic ones burn out in a year, the glass ones are used for medical purposes and are extremely expensive.

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So, I have found a 16,260 umol single LED! Who needs 1000W HPS :wink:


I promised to give a more detailed response to Clones’ post.

[quote=“clones, post:5, topic:1709”]
However, there are so many inaccurate assumptions and conclusions in your post that I could not help but respond. I am responding as a representative of California Lightworks, an LED grow light manufacturer based in Southern California.[/quote]
Ok, let us focus on the inaccurate assumptions here.

[quote=“clones, post:5, topic:1709”]
Your approach represents a typical discussion among commercial lighting manufacturers – it’s all about physics and economics. Period.

However, in the real world, growers do not care as much about physics or theoretical light output as they care about plant biology – how plants use light for yield, quality, chemical profiles, what they can sell their product for, long term operating costs and the environmental impact of their grow strategies.[/quote]
So you should discard scientific plant research? It’s not about economics but it is about long term operating costs?I believe that economics is about long term (or short term) operating costs.

So your key points are:

  • how plants use light for yield
  • quality, chemical profiles
  • what they can sell their product for
  • long term operating costs
  • environmental impact of their grow strategies.

Two of these points are economical, one is about quality, one is general about light utilization (which I responded to with the Bugbee research and our own research), and one is environmental.

So let’s get into quality (chemical profiles) and what they can sell it for first (as these are very much related). We do not disagree that you can grow a better quality plant with a better spectrum. We promote plasma lighting as supplemental source to HPS when growing indoor, as it not only adds a fuller spectrum, but also UVA and UVB. Furthermore, instead of growing indoor, we promote growing in a greenhouse for sustainability. The sun is there our major source of quality light, HPS is just used supplemental, a are red and blue LEDs (which, as discussed, offer a smaller bandwidth of spectrum). However, the size of many LED fixtures still intercept too much light in a greenhouse.

As for the costs: I see that different. As many researches have already shown that yield is not necessary spectrum dependent, you need to have more efficient lighting to get more. So PPF is still an issue. I understand that many LED manufacturers do not want to publish PPF, as it makes their fixtures look bad, so they resort to marketing terms such as “30% more efficient”, but that is just avoiding the obvious and also it is misleading. You may not agree with me on the importance of PPF, but it is still one of the important indicators of fixture efficiency and therefor also an important factor in calculating ROI.

I agree that, when looking at the whole picture, you should take spectrum into account. But spectrum primarily affects morphogenesis and in some way quality. But photosynthesis is still based on photon count, not on the energy of the photon.

So you should only give them red and blue? About the discussion with infrared: This is not wasteful. Given two fixtures, one LED and one HPS with equal efficiency, LED wastes all its heat energy by dissipating it to the back of the fixture, while HPS brings it to the crop. Both fixtures can be regarded equally “wasteful” but you ignore the fact that infrared is actually also beneficial to the crop. The sun has 53% infrared.

You are unfortunately mistaking luminous flux readings for PPF readings. Green LEDs are not very efficient for making PAR light. Humans register green light as very intense, as the human eyes are sensitive according to the photopic curve. The only way to make efficient green light through LEDs at this moment is through phosphor coatings. I refer you to the green light research and the spectrum of the sun. It is the reason why most LED manufacturers use only red an blue LEDs as their primary source. Not green.

[quote=“clones, post:5, topic:1709”]
Designing a grow light to maximize PPF ratings is not the goal. The goal is to provide the best possible spectrum at the best possible efficiency for the specific plants species and grower objectives.[/quote]

You refer to McCree for the most efficient spectrum, but you dismiss his conclusion that most plants have the same action spectrum for photosynthesis, according to the same research. It’s great to provide a good spectrum, but it is no use doing that with an inefficient source.

[quote=“clones, post:5, topic:1709”]
HPS is a fixed spectrum and can only change slightly by changes in pressure. As the pressure increases, the spectrum shifts to the red, as bulbs get old the pressure decreases and the spectrum shifts more to yellow/green. Time to change the bulb again![/quote]

The lamp is not changed because of spectral shift. HPS is one of the most stable as for spectral quality, you are mistaking HPS for MH, which has a huge spectral shift over life. We change lamps when they emit about 4% less light as initial, as this is economically a good choice. What are you going to do with your LEDs over 5 years, when the constantly emit 5% less light? Or on shorter terms, when they emit consistently 3% less light than initial output? Add more LEDs to compensate?

[quote=“clones, post:5, topic:1709”]
PPF ratings between two HPS bulbs or fixtures is meaningful. PPF comparisons between two LED fixtures with identical spectrums is also relevant. PPF comparisons between HPS and LED is highly misleading if not irrelevant – in the same way PPF comparisons between two LED fixtures with different spectrums is misleading[/quote]

I disagree. PPF is one of the indicators of efficiency of the fixture, also when comparing different spectrums. Again, photosynthesis is based on photon count, not on photon energy. Blue photons require up to 1.6x as much energy, so in most light sources, such as MH, this leads to a lower PAR/W efficiency. Not so much with LED though, which is why blue LEDs were such an important development, leading to potentially more efficient LED light and through phosphor technology more efficient wide spectrum, as orange and green LEDs “suck” in efficiency. Still, again, for photosynthetic efficiency PAR PPF counts.

I hope you can elaborate about the spectrum in a HPS lamp is used inefficiently. Again, plants care very much about how many photons they are exposed to, if in the right range…

I somewhat agree. However, it is reaching a platform at the moment, while not getting much cheaper at these high outputs. It is evolving for sure and we will see an increase over the coming five years. The higher the efficiency, the more difficult it will become to reach even higher efficiencies. The waiting is for lower costs at high efficiencies, and that point is coming a bit closer. The most efficient LEDs are red LEDs, at about 3 umol/W (in ideal circumstances, without optics, at correct temperatures). The best white LEDs do not surpass 2.1 umol/W, and are generally at least 20% less in efficiency than the blue LED’s they are derived from.

If you were able to transform all electrical power into light you would get 4-4.5 umol/W, but that is star trek technology.

Now taking this point of 5% more per 6 months: when do you recommend your customers to jump in? You are saying that LEDs will perform 10% better next year, at lower costs. That does not make a good argument for a long time investment in them now. And that is one of the primary reasons why we have not brought out an LED fixture yet. Imagine that we would have sold this 2 years ago, and now we have to tell this grower that we have one that saves him 20% more energy than the one we sold him to be used for the coming 5-7 years… How does that make him competitive?

For at least 5-7 years. We will see much more hybrid installations in the coming period.

I have added that analysis for you.

Now this would be a valid comparison if you would be able to replace a 1000W HP with a 600W LED fixture. However, this is unfortunately not the case. Take a look at my calculation.

And even in this best case scenario, the only 18% net savings you haven’t taken into account light losses which are permanent in LED, costs of financing, and for example heating costs versus cooling costs, though that will be climate dependent. Also you are only looking at indoor facilities, while we grow towards more greenhouse facilities.

As I, and you, already described, nobody is going to use current LED lighting technology for 10 years if the light maintenance is not better and the efficiency of LEDs keeps increasing and prices going down. 5 years would even be stretching it in this industry.

[quote=“clones, post:5, topic:1709”]

now here we completely disagree. This would mean that you would use only part of your fixture for lighting your crop in various stages, decreasing the PPFD on your crop and not fully utilizing the efficiency of your fixture, increasing the costs per umol. We believe in rightsizing the light for the planned use. The spectrum of the sun does not change either over the seasons, specifically not at the original place on earth where these plants origin from. Most professional LED manufacturers agree with this. Look at Valoya’s last presentations and whitepapers.

Our customers still get huge energy rebates on DE HPS fixtures in horticulture. A++ energy label. Start recycling programs.

[quote=“clones, post:5, topic:1709”]
What do we do with the HPS bulbs after they are used? They contain mercury and many of these bulbs end up in landfills contaminating our water and air supply.[/quote]

In the EU we have a recycling program. Now I know that is not high on the agenda in the USA, specifically not with the current administration, but that is not a technology based issue, but a policy en environmental responsibility issue. Trump for example promised more “clean coal” - see what this does to Appalachia.

If you want to talk environment, move towards greenhouses.

[quote=“clones, post:5, topic:1709”]
In summary, Theo, I will make you a friendly wager. In five years, there will not even be a debate regarding the best grow light technology and you will no longer be selling HPS. A hundred bucks?[/quote]

We are not talking about the situation in 5 years, who knows a new disruptive technology will emerge coming years. I bet LED will have a much more dominant position in 5 years, but we are talking sales and comparisons now. We agree that HPS is a mature product, but it is not end of lifecycle yet. In five time years things will be different for sure.

Again, I am not at all making a case against LED. I am just warning against false and incomplete/slanted/colored information from many LED manufacturers and I call upon them to stop spreading false information or non-information. The LED industry is incredibly hurt by those companies and it carries the “snake oil” stigma initiated by early LED manufacturers who claimed double or twice the efficiency of HPS. Now, with new technology, some are still doing that. This makes them completely unreliable.

Again, if you have looked at where I am coming from, I have no interest in changing my job to a sales or technical position at an LED based company. I am responsible for product marketing and innovation at Gavita, and yes, we will bring you LED technology as well.