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

I’m sorry the pictures are a bit low resolution, that’s a forum limitation. Here is the PDF

led vs hps.pdf (97.3 KB)


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: