Guess I should give some details about the heatsink.

It's copper (at lest it looks like it might be aluminum inside)
about 1/4 pound
3.5 inches wide by 5 long ish
20 or so fins (1/2 inch deep)
small fan (will be powered on)
Plastic covering for better air flow

This post was edited by Newguy27 on Sat, Feb 22, 14 at 1:45

The 20-30watt LED chip modules "will" produce a lot of heat. I think the ones you referenced (20w & 30w) draw approx. 700ma with a forward voltage of 30-34v ~ although, I could be wrong.

I really don't know if the ATI heatsink "alone" would be enough for passive cooling, but the heatsink/fan combination sounds workable. I would try to keep the heatsink exposed to as much air as possible, and not enclose it. Give it a try... beats having to buy a heatsink.

found a few 20 watters'ers (led and drivers) on ebay auctions for cheaper going try to to snipe one of them for 50-70% of the buy it now prices.

Thanks for your feedback.

I bought a couple of the 50W Leds warm white. I did some measurements with a meter of current and lux and took some thermal pictures of it on the heat sink. If you read the whole thread, its just me and another guy doing some research. Were growing Orchids. I have been using T8 florescent tubes and although the Leds are brighter if you compare I think the florescent are better. Primary because a 4ft tube covers more space and a single led is more of a spot, so to get the light evenly over 4ft would be very difficult, and the price is about the same. I not through with the research and my conclusion is up for debate. Here is the link. http://www.orchidboard.com/community/growing-under-lights/74275-cheap-ebay-diy-led-2.html#post658048

Thanks for the topic link.

My grow box is rather small (4x4 only using half atm) I thought about doing florescent tubes when building it but decided to try LEDS b/c the longer life and I had the heatsinks laying around.

ATM I have:

50w warm white on a quad core heatsink
*78-90F with fan on
*no lens
*Fan wire come loses once it probably hit 140-150f couldn't touch it

40w red/blue PCB with lens in a box with a fan
*gift from a mate something about red/blue light does better
*Temps hard to get but probably low with the 120mm fan going

30w cool white on a old P4 heatisnk
*78-85 with fan on
*no lens

23w CFL with reflexer
*going replace with a 30-50w led once I get a hold of another CPU heatsink

all placed in a diamond shape (2 foot wide 1.5 foot long) 8-12 inches above the plants. The new 20w would go in the center were the light is weakest.

Trying to grow a dwarf tomatoes and peppers they seem to be doing fine ATM just some of the tomatoes leafs started to curly (near the middle) so I think the 20watter would help.

The goal is 2xdwaft tomatoes, 2x peppers, and maybe some herbs on the side.

This post was edited by Newguy27 on Sat, Feb 22, 14 at 21:03

The led Watts you name are real light watts not equivalent. So you have 143 real watts or light without taking the color into consideration you have approx 8580 lumens. I am blooming cats and onc orchids with 4 2700 lumen t8 tubes or 10800 lumens and a little afternoon sunlight through a tinted glass window. So adding another 27 watts by replacing the cfc gets you to 8820 lumens (if my math is correct. Remember that Cfc is not directional but the leds are. You you will be really gaining more light on the subject. I bought 50W warm white leds with driver for $18 off Ebay. There are big arguments about using res/blue vrs warm or cool white leds. I have done just fine with approx 3500k (warm white) Fluorescent. They say 5000k is good for leaf groth and 3500k is good for flowering, but they also arguer about that. One guy has posted here that it really doesn't matter and says there a long thread about it. Im looking for it.Right now I do not see any advantage over T8 florescent tubes over leds. A lot less fiddling also. You can buy a good 4 tube shiny reflector hood with electronic ballast for $49 on Amazon, funny $11 shipping for 1 but only $6 for 2.