Nice response, Wheelo,
As to this 'someone who wants to grow a pound cheap and easy has to stick with HID for now.' is true unless you're being ripped off @ the rate of $0.27/KWH [can be even more on the punative tier system.] I'm not a mathmagician, but @ that rate, a 1KW running 18hrs/day, 30 days/ month costs $145.80. If you simultaneously run a 600 watt 12/12 for the same period it amounts to an additional $58.32 for a total of $204.12 [Ouch!] Now I realize most of you are not paying through the nose like that, but some of us are. The irony is that the powerplant generating this juice is about 3 miles away. You'll notice that I don't use Lumens or Lux in my calcs. because these are measures of how the human eye sees light. Makes sense when calculating the amount of light you'll need to light your living room, but plants 'see' it differently. This is why I like to use Photosynthetic Photon Flux [PPF]. It is even more accurate than Photosynthetically Active Radiation [PAR] in that it more accurately models the energy absorbed by the plant, rather than the total power between 400-700nm. Since you asked, my source of info for this topic is my Plant Phys text 'Plant Physiology, 4th Ed. Salisbury & Ross 1992' Appendix B 'Radient Energy: Some Definitions, Sec. B.5 Radiation Quantities pp.612-613, and I quote "In the literature of plant physiology, irradience has also been given in units of
illumination rather than total energy or photons. Such units (for example, 10.76
lux=1.0
foot-candle, ft-c) are defined in terms of the sensitivity of the human eye. Plants however, respond to the spectrum in ways quite different from the way the human eye responds,
so such a measure has no value unless exact information is given about the light source. Because plants respond to some wavelenghts of light more than others (Chapters 10 and 20), even a measurement given in
energy or photon units has little if any value when the spectral distrbution is also not given or implied by the describing source" This is why I prefer PPF to PAR, LUX,or LUMENS. "
Photosynthetically active radiation (PAR) Ecologists and others frequently report their measurments of irradience in energy units for wavelenghts from 400 to 700 nm, the wavelenghts most active in photosynthesis. Appropriate SI units for PAR are watts per sqaure meter (w m-
2). Sometimes photon measurements are referred to as PAR, but it would be best to reserve this designation for energy units.
Photosynthetic photon flux (PPF) In a photochemical process such as photosynthesis, the end product depends upon the number of quanta absorbed rather than the total light energy absorbed. A single red photon has the same effect in photosynthesis as a single blue photon, for example, although the blue photon has more energy. Hence, in recent literature it has become common to refer to the number of photons per unit area per unit time. Instruments that respond only to light to light between the wavelenghts of 400 to 700 nm are often used; these may be suitably filtered and calibrated to read in micromoles m-2 s.-1. During recent years and continuing until the present, not all plant physiologists have been aware of these conventions, so both W m-2 and micromoles m-2 s-1 have been refered to as PAR. Note that the source is required to equate PAR and PPF and that PPF always refers to micromoles m-2 s--1 in the wavelenght region from 400 to 700 nm." When you talk watts and I talk PPF, we're speaking different languages [apples to oranges, not apples to apples.] This might help the less scientifically inclined [it also has spectral graphs that illustrate my point.] Light and Plants I used to have a breakdown of how much PPF a plant gets from a 1KW enhanced spectrum MH, but I recently threw it away. I'll try to find it again on the web, but out of 1KW only 126 watts [if I'm remembering correctly] is used by the plant, the rest is either UV, IR, or visable in excess of what the plant can use [e.g., you are correct that contrary to what many think, green is absorbed and used by carotinoids as it bounces around inside the leaf, but when using PAR as an energy measurement, all of the green energy is measured rather than what the plant actually uses as in PPF.] Dude, make me a contact so we can PM these kind of things without clogging up SS's thread [Sorry bro, know it's off topic and way too long, but he asked.]
