lights again

Look up color temperature, lumens, and gram per watt ratios. Everyone on here is going to yell at you to do your research before asking a question like that.

 

well, check in the stickies. there are some other things to consider besides placement, like that a 400wHPS/MH system does not = 4x100w CFLs.

Check out this thread, hope it helps answer your questions.

http://forum.grasscity.com/absolute...s-guide-get-you-started-growing-cannabis.html

http://forum.grasscity.com/general-indoor-growing/263178-all-about-lighting.html

http://forum.grasscity.com/general-indoor-growing/165331-getting-most-your-lights.html

 

Well, I know I'll be kicked around for this answer, but I'd go CFL.

With MH/HPS you have to deal with heat issues. There's a lot more trouble to it if you plan on doing a stealth cabinet grow.

Another isseu around heat from MH/HPS bulbs is that they have to be placed at least 1 ft away from the plant, else they'll simply burn. Idk about the 400W, but I'd guess ppl place them from 2 ft to 3 ft away from the plant cannopy, the only places that receives direct lighting.

Since lumen output is a quadratic formula in relation to the distance from the light source, and the lumen represent on the bulb is at 1 ft away, placing the MH/HPS 2 ft, and 3 ft away from the plant would divide the lumen output by 4 and by 16 respectively.

As for CFL's, they can be placed as close as 1/6 ft of the plant, thats a 2.78x increase in lumen output on the plant. Quite impressive, I'd say.

Another thing about CFL's is the heat issues are much smaller. The bulbs don't need no reactor. You won't need any serious cooling system (simple 12V 4" intake/exhaust fans will do).

And, most important in my opinion, is that 4 CFL's can be set to distribute light more evenly through the plant, reaching side and lower branches, au contraire to the MH/HPS bulbs, that shed light mostly on top.

Ok, for closing the whole thing.
There's a lot of discussion around CFL's and HID/MH/HPS. I'd say people use what suits them best. I like CFL's and they've done great for me on my first grow. Other ppl like HPS/MH best, but they also grow more plants. I grew two, one was male (got the axe) and the other was female. Se is currently on the second week of flowering under 4x25W 2700K CFL's. It's healthy, but won't produce that much. Since you're going for 4x this wattage, I'd say you'll do much, much better.

 

Rob Zombie,
I think you are referring to the 'inverse square law' with your reference to the quadratic formula? This law only applies to unreflected/uncollimated light such as a 'naked' bulb. Most HID lights are used with reflectors and most cfl grows are not, so comparing the lumen output of the two systems versus distance from plants is comparing apples to oranges.

 

Let me just say this, a 400w MH is a beast. I have one and used it for veg on just one plant (bit overkill some would say, but I beg to differ). I got a MUCH MORE rapid growth with MH than I have before with CFLs during veg. By the 4th week the thing was a bush.

I would agree that you can spread light out more evenly with more lights, which I do also. I have a 400w MH overhead and a 150w HPS on the side.

 

@johnk

Well, man. Simply put some reflectors there and it's done. And yes, it's the inverse square law. Pardon, english is not my primary language.

 

Good info guys just gotta drop the word about the T5 florescent light fixtures (with reflectors). They work completely amazing if used right for flowering. Ive gotten over a half pound of some of the best weed you've ever seen from a 324W light.

 

The difference:

First of all, are we talking about CFLs of 100 actual watts? I doubt it. That is a marketing gimmick known as "equivalent" watts, which has some meaning when comparing CFLs to household incandescent bulbs but has zero bearing on growing MJ. Those bulbs most likely are 23-26 actual watts each, so one big difference is that the CFLs I believe you are describing are collectively using only one quarter the electricity as the 400w HID.

Second, HID is much more efficient at turning watts into light than CFLs are. A typical 23-26w CFL is rated around 1600 lumens, so 4 of those would be 6,400 lumens. Using 16 of those -- enough to equal the energy draw of the 400w HID -- would be 25,600 lumens. By contrast, a 400w HPS is rated about 50,000 lumens, so double the light per watt.

So...if we are talking 4 CFLs that are 23-26 actual watts each, the comparison is easy: The 400w HID will deliver eight times the lumens.