A WORD ABOUT LUMENS I have noticed a lot of confusion and misinformation regarding the lumen output of peoples' lighting setups. I have noticed a lot of growers quote the output of their lights as a sum of the lumens from each bulb. This, however, is not really how light works; instead, if one were to place two 1000 lumen bulbs side-by-side and measure the output from 1 foot away you would measure about 1000 lumens. More point sources (bulbs), however, do increase your available optimal space and coverage so another bulb is still a good thing. Because of this phenomenon, the falloff rate (penetration) of the light remains constant, no matter how many bulbs you use, according to an inverse square function (x = l/d^2) where x = lumens at d feet, and l = lumens at 1 foot. This is why you can't grow a 5 foot plant with a bank of 23w CFLs (1500 lumens at best) hanging above. if we plug in the numbers we get 1500 at 1 foot, 500 at two feet, 166 at three feet, and 94 lumens at four feet. This applies whether you are using one, or one hundred. (one could surround the plant with bulbs, but that's totally inelegant and impractical) A small 150 watt hps however puts out a respectable 16000 lumens at 1 foot, 4000 at two, 1777 at three, and 1000 at four etc... So, long story short... get an HID light, in the long run you'll save money, sweat, and tears. PS the jury is still out, but I'm beginning to think that HPS lights run cooler than CFLs watt for watt, check out this link: http://www.rollitup.org/general-marijuana-growing/28192-another-cfl-vs-hps-facts.html
Good info. I did not know how lumens really worked, I guess I should pay more attention to my light placement. Thanks for the research.
If you can't add lumens, then my 8 42 watt CFL's only equal 42 watts, correct? I'm not exactly clear on this. Could you explain further, or differently? Also, I'm unsure as to why the same watts but different style lights equal different lumens. The HID style lights have a higher lumen output per watt, correct? Is that why I hear about HID giving better canopy penitration? Thanks, Bill
Indeed it is. Besides, we need to be talking about lux, not lumens. It is all about how much lux is hitting the leaves. See http://en.wikipedia.org/wiki/Lumen_(unit)#Differences_between_lumens_and_lux
I think it is important to remember the context here. In a strict sense this is incorrect info, I agree. But in the context of how MJ growers talk and think the main point is valid. Lumens are a standardized measure of light output designed for comparing one bulb to another. It is not a measure of light intensity per se. The amount of light actually falling on an object is also a function of the distance that light is from the object, so lumens does not measure amount of light received. Technically lumens measures the amount of light on a one square foot area from a light source one foot away. It is based on measuring candlepower, the standard unit of light amount/intensity. And another oft-overlooked point about lumens -- it is a measure that adjusts for the amount of perceived light falling on an object based on human perceptions of light (certain wavelengths look "brigher" or "dimmer" to our eyes even if the amount of actual light energy is the same). So it most certainly is an imperfect measure. While it may be true that you can't literally add lumens -- because lumens is a rating of a bulb -- we MJ growers talk about lumens and watts as shorthand ways to describe actual amount of light delivered (even though neither of these actually measures that). So from that standpoint you can add lumens together. If you take a light that gives off 1000 lumens and put two of those side by side, the illuminated object will have more light on it and so, to the MJ grower's way of looking at it, does have more lumens on it. Of course, since those two different bulbs can't occupy the same point in space, those bulbs won't have the exact same distance to the object so you don't literally double the amount of light shining on that object. But if the "object" is a plant with a 2x2 canopy then there are many actual points of measurement, and having more light over more of the canopy is needed. The key point here, I believe, is that you cannot add lumens when gauging light penetration. Having a whole lot of low-lumen bulbs will not penetrate any near as well as a single high-lumen bulb. You have to think about both light intensity and light coverage to grow well.