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Comparing lights: pinning down reliable parameters

Old Salt

Member of the Month: Apr 2019
The McCree curve came to be by measuring the photosynthesis of a species of algae in response to various wavelengths of light. I think there is more to it than just that. One of my arguments is different strains of cannabis reflect wavelengths that differ from other strains. Take the purples for example. They reflect some of the blue and red wavelengths. My gut instinct seems to be valid as a recent study at a Canadian University found it was the intensity of the light that governed the yield, not the spectrum. Here's the link: The Impact of Light Intensity and Spectrum-Tuning on Cannabis Yields
 

TorturedSoul

Member of the Month: May 2009, Oct 2010, Sept 2017
I'm guessing it's both - that both spectral content and intensity / number of photons play a part. I couldn't even begin to guess about how to "weigh" the two against each other, though.
 

YellowBelly

Well-Known Member
The McCree curve came to be by measuring the photosynthesis of a species of algae in response to various wavelengths of light. I think there is more to it than just that. One of my arguments is different strains of cannabis reflect wavelengths that differ from other strains. Take the purples for example. They reflect some of the blue and red wavelengths. My gut instinct seems to be valid as a recent study at a Canadian University found it was the intensity of the light that governed the yield, not the spectrum. Here's the link: The Impact of Light Intensity and Spectrum-Tuning on Cannabis Yields
So, any old photons then, as long as there's lots of them? That would make sodium tops then. If one says 'white light', it's obvious that will be the best light because all wavelengths are equally produced and there ain't no light yet with a CRI of 100. You can produce twice as any red photons as blue ones for any given wattage, so a pure red one would be more 'intense' than a pure blue one... if photon number/second is the metric. I have problems with that idea being taken in isolation as the only arbiter of yield wrt lights.
 
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Old Salt

Member of the Month: Apr 2019
So, any old photons then, as long as there's lots of them? That would make sodium tops then. If one says 'white light', it's obvious that will be the best light because all wavelengths are equally produced and there ain't no light yet with a CRI of 100.
They used broad spectrum lights, and compared them with blurples and HID lights.
 

Barney86

Well-Known Member
Yeah I'd say power is much more important than spectrum for yield. I've got 10 year old mars LEDs that they stopped making before I even started growing. Fucking useless on paper but still drop 20oz per meter at 480w. The buds definately not as good as when I go CMH then hps to get a better spectrum but theres just as much of it.
 

Old Salt

Member of the Month: Apr 2019
what's a broad spectrum light? Examples would clarify. I would call a cmh 930 broad:

phillips 930.jpg
Pick any Timber or HLG light. The 'white' LEDs and COBs used in these fixtures are mass produced for other lighting markets, but are used by these manufacturers for horticultural purposes.
 

YellowBelly

Well-Known Member
Yeah I'd say power is much more important than spectrum for yield. I've got 10 year old mars LEDs that they stopped making before I even started growing. Fucking useless on paper but still drop 20oz per meter at 480w. The buds definately not as good as when I go CMH then hps to get a better spectrum but theres just as much of it.
That's interesting. Maybe it requires certain wavelengths to produce the terpenes.
 

Old Salt

Member of the Month: Apr 2019
That's interesting. Maybe it requires certain wavelengths to produce the terpenes.
I really don't know. There is a lot we still need to learn about how light affects plants. We may get indications from home growers, but that will come as a byproduct of our hobby. Most of us can't run true side by side comparisons, and run the tests to find out exactly what's in our harvests. These will need to be run by research facilities.
 

YellowBelly

Well-Known Member
I really don't know. There is a lot we still need to learn about how light affects plants. We may get indications from home growers, but that will come as a byproduct of our hobby. Most of us can't run true side by side comparisons, and run the tests to find out exactly what's in our harvests. These will need to be run by research facilities.
Yeah, true. I definitely won't be buying blurples, even though Barney finds them ok for veg. I just can't stand the colour of them. Interestingly, the shop I got my CMH from has gone all out for CMH and made a website specifically for it. I got chatting to the owner because he sent me the wrong bulb and I rang him about it. He says I'll be well impressed.
 

Old Salt

Member of the Month: Apr 2019
Yeah, true. I definitely won't be buying blurples, even though Barney finds them ok for veg. I just can't stand the colour of them. Interestingly, the shop I got my CMH from has gone all out for CMH and made a website specifically for it. I got chatting to the owner because he sent me the wrong bulb and I rang him about it. He says I'll be well impressed.
I don't doubt it. I have to be careful about heat in summer as I don't have air conditioning. That's one area where solid state devices come out ahead. During the winter months, I wouldn't mind so much as the heat and humidity of the tent can be vented into the house and used there.
 

YellowBelly

Well-Known Member
I don't doubt it. I have to be careful about heat in summer as I don't have air conditioning. That's one area where solid state devices come out ahead. During the winter months, I wouldn't mind so much as the heat and humidity of the tent can be vented into the house and used there.
Yeah, I imagine it's a big deal in some countries. Here in Blighty we don't see above 25C often. I could quite happily grow all the time on this Phillips Sodium Green Power 600w but I imagine the CMH is better. Shall find out soon. This is my plant under the Philips dimmed to 250w. I've photographed it under T5's for better colour:

White Rhino 21 Days.jpg
 

TorturedSoul

Member of the Month: May 2009, Oct 2010, Sept 2017
Interestingly, the shop I got my CMH from has gone all out for CMH and made a website specifically for it. I got chatting to the owner because he sent me the wrong bulb and I rang him about it. He says I'll be well impressed.
Do you suppose he'd be interested in becoming a forum sponsor/advertiser? I don't think there are any entities on our list of forum sponsors that specialize in ceramic metal halide lighting. (But I could be mistaken.)
 

YellowBelly

Well-Known Member
Do you suppose he'd be interested in becoming a forum sponsor/advertiser? I don't think there are any entities on our list of forum sponsors that specialize in ceramic metal halide lighting. (But I could be mistaken.)
Nice idea but he's UK-based and it's not legal. Apart from that, he doesn't know what I grow, although I strongly imagine he's not naive as to the interest of the majority of his clientele. If it ever seems appropriate I'll ask him.
 

Lowrider72

Well-Known Member
Im in on this thread, Its an interesting topic.
CMH is 3100-3200K....
very similiar to old MH yet the CMH plants are always healthier due to spectrum being more complete.

Go 4200K bulbs, get closer CRI of 92%+ but suffer in flower where 3200K bulb does better at 87% CRI.

Its spectrum related, you want plant health, with healthier plants come bigger yields. They want to uva uvb ir etc, to be complete.
They also use a lot less feed for same results under cmh spectrum for some reason....unknown on that.

Anything full spectrum and over 500uMols a sqm coverage will grow top buds.
 

Barney86

Well-Known Member
I've spoken to quite a few guys that grow solely with those 315cmh, the cool looking ones with the big solid hood. Every one of them swear it makes stronger buds than HPS.
I don't know much about lighting (obviously or I wouldn't still be using those blurples lol) but maybe one of you guys would know if there's a logic behind that relating to the spectrum?
 
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