Introduction to Lighting

[jjng5]

Great guide. Is it possible to use too much light on seedlings? I have 6 seedlings growing under 7 26W CFL's and they have been yellowing. Is it best to start of with only a couple bulbs and work your way up?

[jzchillin]

Originally Posted by jjng5

Great guide. Is it possible to use too much light on seedlings? I have 6 seedlings growing under 7 26W CFL's and they have been yellowing. Is it best to start of with only a couple bulbs and work your way up?

generally with cfl's the more the better. at the moment i have 4 seedlings in rockwool under 2x200w cfl's and they could take more. i keep them typically about 2 inches away, even though they do get a little warm, i'm not really worried about it. i think the yellowing might have something to do with the ph, your soil type or a combination of both. if you are referring to the first petals (the name escapes me) that appear, they usually turn yellow and die. the cfl man i have followed in this forum is Kamel, Kamel's CFL Guide - Grasscity.com Forums. he has alot of cfl grow info in his journal.

[jzchillin]

Originally Posted by IMgreen

yeah it is!

the light distance chart is kinda handy too, do you have it?

sorry for not getting back to this. i have the hps lighting chart but not the mh. you or anyone is welcome to post it in here if you have it.
FC-Chart-HPS.jpg
i think this one is kind of cool too.
light output comparison chart.jpg

[jzchillin]

been awhile since i added anything. if anyone has anything to add feel free...

[kangasaurus]

Does hight of the plant matter? What I mean is, you say that 250W HPS is good for 2'x2' grow space, but does the height of the plant matter? I've read places that, not specific to our favorite plant, the taller the plant, the more wattage you need. So for a 2'x2' grow space with three 4' tall plants, would I need more along the lines of 400W HPS?

[jzchillin]

Originally Posted by kangasaurus

Does hight of the plant matter? What I mean is, you say that 250W HPS is good for 2'x2' grow space, but does the height of the plant matter? I've read places that, not specific to our favorite plant, the taller the plant, the more wattage you need. So for a 2'x2' grow space with three 4' tall plants, would I need more along the lines of 400W HPS?

If you have a cool-tube or are able to keep the temps down you can use a 400watter, but the plants can get radiation poisoning (sounds strange but it is true), if the light is to close regardless of temps. in the case of a 400watter, i don't see that problem. i personally, have used a 600watter, with a 900cfm fan to cool it, in a 3'x2.5' box. in a box, the height of the plant doesn't really have an effect on the wattage. everything about 10in below the canopy will die away and only the tops will get the light. 1 thing to note, the stronger the light, the further it will penetrate the canopy and the more dense your buds will be. i have a light penetration-wattage chart somewhere i'll post.

in a room that size i would use a 400watter in a cool-tube