Cool, thanks Clive,ceg4048 said:Hi Ady,Ady34 said:
Well it's not necessarily about equal wattage, it's about equal PAR. Bulbs of similar wattage may in fact have different PAR and this will affect the plant more so than spectrum. When someone makes a comparison of growth using different bulbs it's important that they are comparing apples to apples, unless they are specifically comparing the differences in PAR for different bulb types. So if you want to compare the effects of yellow light versus red light, then you have to ensure that the PAR is the same for both, and that way you will be seeing differences due to spectrum and NOT due to intensity. This is where people make false connections. For example, I can grow plants with simple Tesco incandescent light bulbs, but incandescent bulbs have a very poor PAR efficiency. They emit mostly heat as infrared. Most of the spectrum is in the yellow. and so only about 12% of the energy output is useful PAR, so this makes incandescent bulbs generally inadequate if we want rapid growth rates, but again, that's because of PAR limitation, not because of the yellow spectrum of these bulbs. Fluorescent tubes have a higher PAR efficiency, perhaps on the order of 25%-30%, Halides emit higher still, perhaps 40%.
Yellow light simply gets processed by a pigment that is different than chlorophyll. This energy is then transferred to the chlorophyll. Pigments such as Phycocyanin processes orange and red light, while a pigment such as Phycoerythrin processes blue-green to yellow. The plant simply analyzes the incident wavelengths and produces the pigments necessary to make use of the available wavelengths. This energy is passed on to the chlorophyll, and the chlorophyll reacts in the same way as if it were excited by it's own native blue and red excitation wavelengths. Plants have an arsenal of these auxiliary pigments to deal with any range of colors within the visible spectrum so they can't be "thrown off" just because your light is changed to yellowish or greenish. White light is composed of all colors, so the plant is already doing this conversion and already has these pigments in place. Since plants are descended from algae they have pretty much the same pigments as algae. Whatever light algae can use, plants can use. Whatever light plants can use, algae can use. The problem occurs in plants when you have too much PAR. That's when algae wins. They could each care less about colors. In fact, the main job of these pigments is to protect the plant from too much PAR, and they do this by filtering out and rejecting excess PAR and UV by fluorescing away the excess energy. This is what we see so often when plants "color up" in response to higher light intensity. The pigments become visible because they plant has to produce boatloads of them to deal with Klingon Photon Death Ray fanaticism.
Cheers,
so really we all need PAR meters to more accurately assess our lighting range irrespective of colour renditions or indeed wattage rules. The plants dont care as long as the PAR ratings are within tolerance for available c02 & ferts.
I know this is slightly off topic too, but we know that 5w/g is the upper limit of lighting efficiency where plant fertiliser uptake rates max out, but is there a proven lowest light level for plant growth, whereby no amount of c02 availibility and ferts will compensate? Also with this in mind, is there a general concensus as to a suitable PAR range at substrate level for plants? .....and if you know, how much are PAR meters and do you measure PAR/are PAR measurements with or without the water in the tank? Sorry for this barrage of Q'sceg4048 said:
Thanks,
Ady.
