Effectively using your MH & HPS lights - All about light & distance

Discussion in 'Growing Marijuana Indoors' started by TheFxckingHero, Jun 15, 2006.

  1. Hey, everyone.

    Well, after seeing many people asking how far they should have the light from their plants, and myself being confused about it at times as well, I went and looked up some info. I recently moved my light further from the tops of the plants thinking it was too close and contributing to the problems from accidentally over-fertilizing them, but I've seen some internode stretching and plan to move the light back down where it was before. This should provide everyone with some good information, and I think it'd be a good thread to make as a sticky up top.

    First, I'll put up two charts here showing the foot-candles put out at various distances. A lot of people talk about total lumens being important, and while light intensity is important, lumens and foot-candles are units related to what the human eye can see. Plants don't "see" light the same way we do... but more on that in the next post.

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  2. Thank you so much for posting that, it just proves what i said about lumens per watt useage when using flourescents..

    and now i can see why when i am vegging with flourescents they grow MUCH faster than when under MH or HPS....

    at 18 inches from my plants my 1000w MH the plant is only receiving 15,000 lumens and even if its 12 inches away (which requires very good cooling) they only then get 35,000 lumens.

    Something i can obtain with 8 4ft flourescent shoplights (48,800 lumens) and have them an inch away from the plant and only use up 640Watts (for those who believe they actually use 40 watts per bulb, coz they dont)

    So here you have it, LOW Cost and just as good performance, Flourescents!
  3. Okay, moving on... I had to make two posts to fit all 6 attachments.

    Now, here is the important (and most interesting) part. As said before, plants don't "see" light the same way we do, therefore using lumens and foot-candles is not the best way to rate light intensity for growing purposes.

    "The expression Photosynthetically Active Radiation, often abbreviated PAR, designates the spectral range of solar light from 400 to 700 nm that is useful to terrestrial plants in the process of photosynthesis.

    Chlorophyll, the most abundant plant pigment, is most efficient in capturing red and blue light. Horticulturists say that blue light is the most important for leaf growth and that red light encourages flowering. Accessory pigments such as carotenes and xanthophylls harvest some green light and pass it on to the photosynthetic process, but enough of the green is reflected to give leaves their characteristic color. A glorious exception to the predominance of chlorophyll is autumn, when chlorophyll decays earlier than the accessory pigments that remain to color the leaves red, yellow and orange.

    PAR measurement is used in agriculture, forestry and oceanography. One of the requirements for productive farmland is adequate PAR, so PAR is used to evaluate agricultural investment potential. PAR sensors stationed at various levels of the forest canopy measure the pattern of PAR availability and utilization" (Wikipedia).

    Basically, PAR is the measurement of light (and spectrum range) that plants actually use.

    Here are graphs and charts comparing HID lighting's PAR rating at various distances with the PAR rating of tropical sun near the equator. Beyond 100% is actually a greater intensity than the sun...


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  4. So for those who praise their 400w hps, here are the stats

    4 x 4ft shop lights with 2 bulbs at 40watts = 320 watts (24,400 lumens)

    1 x 400w MH = 400Watts (16,501 lumens at 10 inches away)

    Savings 80 watts or even more savings if you want to match the lumen output at 10 inches by using 3 shop lights (120 watts @ 18,300 lumens)

    Thats a 280 watt savings on electricity bill, not to mention what you had to run prior to cool down the heat from MH and HPS.
  5. Plants see that way yes, but whats most important here is the color temperature, and with daylight bulbs its the same.

    No matter how you turn it dude, dont care at 18 inches away my 1000w MH produces shit to its full advertized lumens.
  6. lol You're right Dier, but please look at the PAR as that is overall what is more important to plants. Lumens can somewhat be used as a general outline of the intensity of the light, but it doesn't account for the right spectrums, so it is not very accurate.... You are right about your flourescents though. The only disadvantage with them is they are only really lighting up the part of the plant they are immediately above... They can't penetrate to the middle or lower parts of the plants as well as a MH or HPS can.

    I think the flourescent shoplights would be great for seedlings and clones up to a certain height, and I'm in the process of setting one up in a wooden chest for just that purpose. However after the plants get to be a certain height, the lower growth would start to stretch, so if you plan on flowering those plants they'd be better off going under the MH or HPS at that point. Of course, the lower growth stretching doesn't matter much if you are using the flourescents for mother plants... then you just have more branching to work with.
  7. Notice your first graph on % of sun power... 100% is what your aiming for, do you see the trend??? the lower wattage the bulb the closer you can put it
    by the time you get to the 1000w bulb your 20-21 inches away, which is even worse than the shitty lumens i posted before.

    lumens is the Brightness, or how much it Illuminates... and we all know what happens to our plants when its not Bright! enough, they STRETCH!

    Like i said, during veg my plants vegging under my 8 flouresent shop lights grow alot closer internode wise and a hell of a lot bushier compared to with the MH or HPS (HPS being worse because it stretches even more because of the wrong color)
  8. This is why you just dont place them Flat on the top of the plants,

    I have in my grow are for flourescents 4 on the top spaced part 2 on the back wall and 2 on the front wall, effectively (much more so than MH penetration) sending light throughout the plant.
  9. lol I agree with what you're saying. This wasn't meant to compare the effectiveness of flourescents. Also, 100% would be equal to the sun, but if you can go higher than that and keep the temperatures down you'd get even more growth.

    Another important note to make (taken from the link in my signature) is that metal halide and flourescents in the blue spectrum also have ultraviolet light. HPS has virtually no UV or UVB light. The most potent varities of pot come from plants originating near the equator and areas of high altitude, where there is the most UV light from the sun. The plants put more energy into trichome and resin production to protect themselves from the harmful UV rays.

    Flowering under HPS will provide bigger yields, but flowering under metal halide will provide more potent product. This explains why a combination of the two is best. Tests of adding UV light from other sources (tanning lights, blacklights, etc.) would be interesting to see....

    EDIT: Oh, and proving the point about PAR over lumens... yes, they stretch more under HPS than MH because of the spectrum being the wrong color, but HPS is brighter than MH. So, you can see that lumens is not really what should be looked at.. know what I mean?

    lol, and again I wasn't saying anything bad about your flourescents. I think the way you have them set up is very efficient and would be a good idea for anybody that has enough space to do that. I don't have the space for it though...

    I also think that two 400w lights on opposite sides positioned closely in a diagnol or horizontal position would work better than one 1000w light from above.
  10. I once posted that i had 4 UV blacklights (100 watts each) in my flower room on Overgrow.com and they called me an idiot, but i knew better, simply because i read :)

    there you have it, my final secret to sticky icky icky :)
  11. As for space, dont need much space im doing my vegging in a regular clothing closet (non walk in) which measures 6ft long 3ft deep and 8ft high.
  12. that's about how my closet it is, but it's more like 2 feet deep, and there's a permanently stuck shelf in there which makes the usable space only about 5 feet high... BUT that's where my HPS is and I don't have any other area like that for vegging (not until I move to an apartment, anyways.) but just outside of the closet in the same room I have a thick 5ft long x 1.5ft wide x 1.5x tall wooden chest that I can perfectly fit a two-tube 80watt flourescent shoplight in... and I think that will work perfectly for growing seedlings and clones for 2 weeks before taking them in to the closet for flowering. will be all sea of green grows from now on so I can rotate plants quickly and still get a good yield... :]

    anyways, enough about what i'm setting up. I hope more people look at this thread and hopefully learn something new. :)
  13. These charts really emphasize the need for a air-cooled hood!

    Flourescents are great and the T5 set up looks awsome, I haven't grown using MH yet so i'm not sure how good it works but I have done HPS and flouro in veg and if I were to do it again I would deffenetly choose flouro's.
  14. hey dier just curious but you said you used 4 uv black lights at 100 watts each were ur (black) lights on during the "on" or "off" stage of 12/12 or were they on 24/7. b/c i read that black lights can't grow plants but does this mean that they would interupt the dark cycle? thank you if u could please clear that up for me. here is a link to my grow they are now 4 weeks into flowering http://forum.grasscity.com/showthread.php?t=98147
  15. Great post Thefxckinhero. Its making me rethink my next grow. I live in a apt with 2 of my boys and we were gona double bunk for about 4 months and use the extra room to grow in. That way we could grow the entire amount of weed we need for the year at once (currently using closet and just growing a 3-4 month supply at a time, growing all year round). I was going to go out and get one or two thousand watters but now I might just get another couple 400s and save on supplies and power bill.

    And deir I am with you about flourescents. I use them from seed to bud. There’s just nothing better for those hard to reach places when heats a issue.

    I'm all so intrested by this black light usage. Do you use it only when the lights are on or do you run it 24/7 and does it really back that much of a diffrence?
  16. I don't think the black light actually grows the plants at all... I probably wouldn't bother trying it out, but if I ever did it would be only when lights are on and POSSIBLY the UV rays would help... that is just a maybe... no way to know how strong the UV rays from the black lights are.
  17. Your My Fxcking Hero! lol
  18. excellent thread, so in my closet (6L X 4W X 8H) I have 2 each ( 2bulb 40w 4') shop lights for the overhead one on each side and one on the back wall (sides and back being vertical) 10 bulbs @2325 lumens color rendering of 84 and color temp of 6500 K. Based on this thread what I have is gonna work... correct??

    Light spectrums for veg vs. flowering is where I get a little sketchy, can I use the same bulbs listed above or what should I switch to. plants are bagseed and I will have 3 in this setup

    thanks again
  19. so the conclusion is: there's no point in getting a powerful light because then you just have to put it further away from the plant, thus defeating the point of its high power?
  20. Question. In those charts about intensity vs distance, what are all those numbers? They aren't lumens, right? Because I understand lumens are measured at a distance of one foot, so the 1 foot mark should match the advertised lumen rating. Again, why fluorescents are better than you think, since yeah they make 2000 lumens at 1 foot, but you don't have them 1 foot from your plant now do you? And as for the blacklight, I've read a lot about em, and as I understand it black lights have no uvb output, just uva which is useless. There are some reptile lights that give uvb, and have crazy results.

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