The only transmission numbers I can ever recall seeing were PAR.

Thanks for sharing all the pictures, Pen. I'm pretty new to this whole Dischidia business, but learning on my feet. Where are you planning on housing the mounted ones longterm? I'm happy to report that my mass Dischidia rooting flat is working well. I haven't lost any and they are all putting out roots. I started spraying them with willow tea, so maybe that will cinch the deal. When Denise and I chatted with Tom, the greenhouse manager who was overseeing the care of that Dischidia collection, he said that Tanya Livschutz had requested a very strict watering schedule, allowing them dry out completely and applying little fertilization. The plants did not adjust well to their new environment, and what ended up working in his specific greenhouse conditions, was a very high drainage setup, daily watering, and a standard tropical fertilization schedule. He said his experience was that the mounted ones did best. Anyway, it just goes to show that there are no hard and fast rules, since those two had success with two completely different strategies, given the same collection.

I think I'm painfully learning that mistake about grow lights as well. I'd actually gone to buy shop lights, but I needed 2' length and the only 2' length fixture they had was "hard wire". Not wanting to burn my garden shed down trying to deal with that, I thought this would be the easier option for just a few dollars more, but now I'm regretting it. These lights are really puny and the cord is so heavy in comparison that they don't even hang straight. It sounds like I should take these back and do a little more shopping for what I really wanted in the first place. I was only fearing that I might be worrying too much, considering this is my first attempt and all. (If I kill these plants it will be for OVER tending, not under!) I appreciate the quotes on the foot candles. I'd been looking all over the site for that minimum number but only came up with stuff on orchids. ;-)

The Prolighting article illustrates the vast amount of utter cr@p that is written by people trying to sell fluorescent hi-bay lighting. For simplicity I would suggest you ignore such comparisons as they are utterly skewed to the point of being lies. Modern fluorescents (T5, T8, or suitable T12) now have efficiencies virtually as high as modern high power metal halides, and the lumen maintenance is somewhat better, although not to the extent indicated in such comparisons which use obsolete technology. There just isn't a compelling difference in efficiencies (it is a given that obsolete technology fluorescent or metal halide is significantly less efficienct and hence more expensive in the long run), and decisions need to be made on the basis of convenience, retro-fitting costs, and usage aspects like dimming and occupancy switching. For us plant freaks there is also the question of spectrum. And such comparisons generally ignore HPS which is still significantly the most efficient lighting for growing. Your more general question about light intensity falloff with distance is a very complicated one and has led to much confusion and more cr&p being written, even by people with great experience of growing under lights. The oft-quoted "inverse square law" or the "exponential" light dropoff is simply irrelevant except for a point source without a reflector. Also, much confusion has been caused by the inherent ability of a bright light source used at a distance to provide light which drops off slowly with distance, a factor which has nothing to do with the nature of the light source itself merely with its total light output. Any reflector focuses the light to a certain extent and the intensity drops off more slowly. Fluorescent tubes do not obey these laws even without a reflector because they are extended light sources. The light intensity from a fluorescent, or an array of fluorescent tubes, drops off more slowly than from a point source like a metal halide. But note this doesn't mean you get higher intensities from the fluorescent, in fact just the opposite. The intensities at a large distance from a fluorescent array or single HID giving out the same total light are the same, but as you get closer to the HID the intensity rises more quickly. It can be hard to think about and perhaps isn't necessary. The crucial aspects are the total light output and whether you can get that light fairly evenly onto your plants and only onto your plants. The only thing of relevance I see from the comparison article is "light meter readings taken at the plant canopy level registered higher for plants growing under the Satellite II". This is crucial! Whatever the lumen output of the various tubes, if that output is not reaching the plants then it is a waste of time. Therefore the comparison is virtually meaningless. Place the metal halide closer and use a fan if scorching is an issue, or water the plants properly. It would be interesting to know the light intensity nearer the base of the plants, particularly as they reach the fruiting stage. Another critical metric would be total yield, either vegetative or fruit. Again, you have to think about the practical considerations of getting an even spread of light over a wide area and I like long tube fluorescents for this, but a solid alternative is a well-enclosed white growing area. The distributed nature of multiple fluorescent tubes also allows creative solutions like arranging the tubes around the sides of the growing area instead of simply above. Just as a matter of interest, the Satellite fluorescents are actually compact fluorescents, effectively an 8' T5 (I think) fluorescent bent in half. 105W and a claimed 10,000 or 10,500 lumens, they aren't clear which. Very expensive, you get identical output and efficiency at lower cost from two 54W T5 straight tubes, although they need slightly more room. Again almost identical output and efficiency and much lower cost from 3x36W T8 straight tubes (36W T8s not common in America, you would have to drop to 32W or look for true 40W tubes), obviously needing more space again. We are in a wonderful position as growers of being able to choose exactly how much light intensity we use, all the way from off-the-shelf $2 T8s, through straight T5s and high-power compact fluorescents, to HID lamps bright enough to burn foliage. The trick is to ignore all the competing advertising claims about which is "best", because none of them are best, they just achieve different things at different costs. Here is a link that might be useful: Satellite II Comparison Test