Light Math Questions

bpiela · Apr 11, 2016

Currently, I am growing seedling on two shelves with 4 x 48" T5's per shelf. The plants love it and but they have now grown too much and are growing into the lights. I have been pruning and topping but I am thinking that I have room next to the shelves where maybe I can move larger seedlings to, pot them up and put an overhead HID or something and let them grow larger. I don't really know the terminology here.

I am thinking there is the grow area that I keep my plants in. It can be a square or rectangle but I would guess that it really would be circular if I had one light source. There is the distance from the bulb to the plants and then there is the actual light which is rated by how many Watts it puts out.

I do not know how to calculate these areas/distances with whatever powered light source I can find. I am assuming I would hang the light source off of the ceiling somehow, but I don't really know. I would like my plants to continue to grow and be happy. I do not want to put my light source too far away nor too close, so I would rather not wing this if possible. That is why I am reaching out for some assistance.

Any help is appreciated.

juanitos · Apr 11, 2016

coverage:

distance away:

so a cheap 400w kit. grows a 4x4x4 space essentially and is the best entry level HID setup.

bpiela · Apr 12, 2016

Thank you very much for this info!

So, in this 400W 4x4x4 scenario, the light source should be anywhere from 6 inches to 21 inches away from the plants, right? Just making sure I am reading the charts correctly.

juanitos · Apr 12, 2016

I would just keep at 15" away.

peppers don't need 50klumen lol, thats if you are trying to get super dense weed yield.

bpiela · Mar 8, 2017

juanitos said:
I would just keep at 15" away.

peppers don't need 50klumen lol, thats if you are trying to get super dense weed yield.

What about the cheapo LED lights on Amazon? HIGROW, CrxSunny, VIPARSPECTRA, MAXISUN, BLOOMSPECT, etc... Would a 400W equivalent LED setup from one of them be fine for a 4'x4' area?

To be honest, I don't know if I can just build my own without some kind of instructions, so I am possibly looking into one of these cheap models. I was thinking LED might be better than HID since that is where the market seems to be going. Of course, I would prefer one that will last a few years and keep my larger plants happy. I would hang it from the ceiling and hope that I don't start a fire in my basement.

hogleg · Mar 8, 2017

On starts (plants to about 14") I run my 400w MH 15"-24" above the tops. At 6" I think you might fry the tops. LED's you can run closer to 6".

bpiela · Mar 9, 2017

hogleg said:
On starts (plants to about 14") I run my 400w MH 15"-24" above the tops. At 6" I think you might fry the tops. LED's you can run closer to 6".

Thanks! I believe that I didn't state my question clearly enough...

So, I am trying to set up another station in my basement to put plants that have outgrown my shelves where I start my seedlings. Last year, I had many issues with plants growing into the lights and then other plants not getting enough light, etc. I was thinking about a place where larger seedlings (12") can be moved to and I would hang a light source from the ceiling. I am not certain if I will need a 3' x 3' area or maybe 4' x 4' if I include my OW's.

I was thinking maybe those cheapo LED lights might be a decent way to go. Alot of folks on this forum are handy enough to build their own. I don't believe I have the patience for that. If HID lights are better for this kind of thing, maybe I should just go with that. Just looking for thoughts/comments/etc on these LED lights that seem to have come down in price since last year.

Thanks again!

A Spicy English Cheapskate · Mar 9, 2017

bpiela said:
Thanks! I believe that I didn't state my question clearly enough...

So, I am trying to set up another station in my basement to put plants that have outgrown my shelves where I start my seedlings. Last year, I had many issues with plants growing into the lights and then other plants not getting enough light, etc. I was thinking about a place where larger seedlings (12") can be moved to and I would hang a light source from the ceiling. I am not certain if I will need a 3' x 3' area or maybe 4' x 4' if I include my OW's.

I was thinking maybe those cheapo LED lights might be a decent way to go. Alot of folks on this forum are handy enough to build their own. I don't believe I have the patience for that. If HID lights are better for this kind of thing, maybe I should just go with that. Just looking for thoughts/comments/etc on these LED lights that seem to have come down in price since last year.

Thanks again!

From what I've read around the web, mostly on Mj forums I get the impression that white led cobs tend to be the most efficient source of light available for growing. I currently have my own plants under a cheap led floodlight which I changed out the cobs and drivers for better ones. A lot of people do well with blue/red. "blurple" lights but I would be very skeptical of there claims of "equivalent power" and you will want the true power draw at least close to the hid light it'd be replacing. Metal Halide and HPS are definitely the best bang for buck lumens/price especially as you get into the 100s of watts.

willard3 · Mar 15, 2017

3000 lumens per square foot of plant canopy is good.