Chlorophyll utilization of bulb spectrums, CMH & HPS.

Did this cross comparison of charts of bulb spectrum (Philips MasterColor CMH, Generic HPS) against chlorophyll absorption rates. It seems to me that HPS bulbs are completely unsuitable as grow bulbs. Yeah, they produce a LOT of yellow/orange light, which falls directly into the area of the spectrum that plants barely use, either in veg or flower, both chlorophyll a & b don't use it, but they got almost nothing else. The difference in spectrum for enhanced spectrum HPS like Super Horti isn't all that great, slightly better, but still with the majority of light being of a lousy spectrum.

Is there some other factor that plays in? I don't get it. Why are HPS used by anyone? They throw off like like giant incandescents... So what if they are efficient at it.

I've looked at MH vs HPS and I'm convinced that a MH bulb is better for growing/vegging a plant (which most people do) as it pumps out more blue energy rich light as opposed to the longer wavelength that HPS puts out..

your lower wavelength/higher frequency light that is put out by an MH has more energy and will drive the ETC within your chloroplasts more and thereby produce more energy for the plant during growth.

however HPS being a "warmer" more yellow/red spectrum bulb helps with flowering when changing your light period from 18/6 to 12/12.. although you can still flower with an MH bulb

also watt for watt HPS produces more lumens..

cmh seems very rich in greens. Isnt that the one of the only wavelengths of visible light that plants do not absorb? Im not trying to troll im actually wondering.

That's true.. at least green plants.. the reason you see green is it is the wavelength that is reflected.

chipmunkproof said:

cmh seems very rich in greens. Isnt that the one of the only wavelengths of visible light that plants do not absorb? Im not trying to troll im actually wondering.

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Plants do use green light, though much less efficiently compared to blue/red light. Plants also use yellow light very inefficiently, which is like 60-80% of the light put off by an HPS. A much lower percentage of CMH bulbs is green. The specs suggest that they actually put out more than either traditional metal halides or HPS in both the blue and red spectrums, with little wasted light in the middle. You can see how on the charts for HPS there is almost no relative energy throughout the blue and red spectrums. there are little peaks, but nothing much. On the chart for the CMH it is fairly even across the board, which means even distribution of relative energy, the first true full-spectrum HID bulb.

ottawaliquid said:

That's true.. at least green plants.. the reason you see green is it is the wavelength that is reflected.

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Not entirely true. Plants will grow under lights that put out almost entirely green and/or yellow light. The absorption and utilization is fairly inefficient, but more green or yellow light will still produce more growth. That's why HPS bulbs are even capable of being used as grow bulbs at all; the plant adapts to absorbing a ton of yellow light, and uses it, albeit very inefficiently, causing some stress and poor utilization of potential total light energy. HPS bulbs are incredibly efficient, and pump out a ton of lumens per watt. The sheer power of the bulbs is the only reason they compare with the same wattage of metal halides and other fuller spectrum bulbs. The plants certainly don't like that lousy yellow light and will hurt in quality for it.