Yo undercover- you asked a ways back about comparing bulbs w similar outputs/spds. This is actually a huge issue the way I understand (from the pdf I posted like 40 pages back--one of my first on the thread) as there is no known meter which can reliably compare an artificial emitter (light bulb etc in their varied forms, diodes and so on) to solar irradiance. Boom. Fail for anyone trying to claim they are reproducing sunlight as opposed to claiming to try to emulate sunlight, no meter has been able to do an accurate (at least as far as peer-reviewed science via journals is considered) comparison. Yea I know you can walk outside with your "light meter" and get a number, probably a really high one, and come stick it under a grow bulb and complain or brag depending on the numbers. But the problem is that we have trouble accurately measuring all of the wavelengths at once. All are important in different ways because they are ALL available to the plant from the sun, normally. Full spectrum growing is an important concept because you can see some really bizarre morphologies from "low-quality light" aka deficient spectrums.
I submit 2 ways of measuring the lights.
1) reverse spectroscopy-finding chemical compounds which have peak absorbance/reflectance etc at certain wavelengths/concentrations and rig a spectrometer which can compare it to recorded outputs from a light of the same type...? I'm assuming some of the error comes in the drastically changing output types.
2) Target plant morphologies with low-quality dialed in spectrums.
For example phototropism with blue band, you should be able to arrange a test with even spinach or whatever and same heights/growing conditions, and just move the lights from side to side each day and monitor the pulling power. Put the plants in the middle, do they visibly favor one or the other? By my understanding, until the light saturation point is hit, the phototropism should favor the higher average blue band emission/intensity or some similar relationship of those factors.
If Prof. Craker over at UMass wins this case (
http://www.maps.org/research/mmj/dea_timeline/ It looks so favorable but you know how these things go) then maybe I'll submit some research in this area.
What is useful is comparing lamp to lamp, but major issues arise in the individual measuring devices, the pdf I posted is an analysis of like the 3 leading brand PAR meters.
Sorry if this is all greek to you.
BTW all after you hit the lifespan of your bulbs and retire them from your grow, if you have another unit, they are probably still good to go for growing salad greens etc, or my latest idea:
Green manure + Rhizobium inoculated legume preplants for Added N and myco/bacteria population building time, fueled by old bulbs. (you grow inoculated bean seeds in your soil, potted up and ready for your med stock. After the beans are big enough, or you are done fruiting off them--may want to add nutes back to soil if you harvest a lot, think iron, no EDTA pls----you turn the whole bean plant, chopped up if you prefer, back into the soil and let it "compost" for a week or two before transplanting in your clone/popping in your sprouted bean)
MPP
edit:
the morphology tests in "2)" have been performed with many many many plants, databases are full of the published studies, (search "red light blue light xxx", xxx for plant name, just limited wavelngths have been tested on ganj, and honestly genetics play such a large role I've only seen 2 comprehensive studies and they were more about the terpenoid contents than the light, but a savvy eye can glean the details. There is also that flux density study i posted a bit back
edit edit:
http://www.maps.org/media/view/crakers_legal_team_submits_opening_brief_in_lawsuit_against_dea/
has the pdf link for the brief he submitted on December 15, 2011 read the first 50 or so pages, seems pretty tight.