Quick question on LED panels

Supra,

Thanks for this great info. I read somewhere that using a few watts on cooling fans wasn't inefficient on bigger units. What do you think of the build quality and design of the new A51 units? I'm going to read through the KNNA thread.

@Buzerek - I am a medical grower and there are plenty of economic reasons to switch over the LEDs. Plenty of commercial grows are making the switch. Higher quality and more efficiency and longer lasting - when you factor in not having to run 10 tons + of A/C and not having a space re-wired for 100s of amps the upfront cost isn't as far off as you think. In a competitive market doing LED well will pay for itself quickly.

I've been playing around with the design. I think using wide angle lenses will allow me to get closer to the canopy and provide the side coverage I want without the frame taking up the whole space. It will also allow me to use more powerful emitters. 60watt cobs running at 40 watts in a hexagonal pattern is what I have in mind at the moment. 720 watts over 18 square feet with consistent par. Wide angle lenses should let me keep the lamp a foot away with no issues. I have someone willing to help me with parts and wiring so it looks like this is going to happen.

I'm still trying to decide on color values. The white Cree modules I'm looking at come in 2700, 3000, 3500, 4000 and 5000. Maybe use 2700s and mix in a few 3500s for the 'blues'?

Rahz sounds like you are well on yr way. I didn't know there were COB lenses very cool


RE Area51. Looks like they scrapped the reds and XPGs switching to XTE 3700K. If the drivers put out 700mA the LEDs should dissipate about 160 watts so ~$4/watt. Radiometric efficiency in the low 30s IF they got their hands on the very rare top bins and did not specify the bin. I suspect they are running very hot (check actual heatsink temps) but whites can deal with heat a lot better than reds do. I dont recommend all white LED for flowering (if given a choice) but I am open to being proved wrong

I did say lenses, but the cobs I have in mind (CXA series) emit at 115 degrees so no glass will be required.

I thought it interesting that A51 is using warm whites. The person giving me help has also built panels using warm white but chooses a combination of 2700K and 5000K at a 4:1 ratio rather than 3750K alone. There's room for debate regarding the most efficient setup. Plants don't care for green I know, but the question is whether getting broad spectrum red and blue is worth a little green. I can't answer that question but it looks like I'll be going white, so I'll hopefully get some gpw figures eventually to add to the debate.

I'll start a new thread when I start the build. I post any interesting developments here until that happens.

Beside the argument regarding lower efficiency (PAR watts) of white LEDs, I am also skeptical because of its tendency toward leafiness. The HPS spectrum (~2000K) tends to support nice hard nugs with a good calyx to leaf ratio. But they are also slightly lacking in frosting and flavor. So the idea of using warm white and adding a touch of blue for frosting and some reds/deep reds to get hard HPS type nugs without excess leaf.

Last time I experimented with cranking up the whites I did notice increased leafiness in the buds of cuttings I was familiar with. To be fair, back in those days all we had to work with was cool white and I have not experimented since. I see the same leafiness in outdoor buds and in many photos of all white LED grows.

DNA Cannalope Kush. This cut is very frosty but tends to be a bit on the leafy side.
600w HPS nug - acceptable ratio, good frosting. This pic does not do it justice.


Same cutting under red/white/blue LED - calyx/leaf ratio is still good, maybe better. but nugs are frostier

The problem is the world of color has not made it's way to cobs yet.

If you built a lamp with whites would you use only 2700K emitters?

Thatsa darn good point. Mixing 10 watt COBs (Vero18 at 350mA) with 1.5 watt red XPEs might not work out very well in terms of mixing and reach and defeats the point of COB simplicity. From counting boxes I estimated that an XTE 3000K spectrum has ~10% blue output so maybe 2700K has 8%. KNNA recommended a minimum of 15% blue for flowering but Stardustsailor has suggested that less is OK.

It would be sweet if Cree released a blue XML2 or a blue MKR. There is 1 big blue available the Luxeon M. I calculated the C5G bin to be 57.7% efficient at 700mA 50c and it will dissipate 8 watts. Not bad for $11.

I'm playing around with grow theory and wondering why blue is standard for veg. I can understand the desirability of blue in a sog, but in my scrog setup I have 3 plants vegging out to fill an 18 square foot area. For this reason it seems long internode length is desirable for the first several weeks. Blue would be added at 12/12 to slow vertical growth and provide a color balance for flower production. Let me know if that seems crazy.

I am very happy with the veg period I'm getting using 3000K CFL bulbs, not so happy with the stretch I get the first 3 weeks of flower.

In the above pic you can see the original layout. Outer lights (top and bottom of pic) would be off during veg, but this would be the opposite of what I'm considering now.

After thinking about it I'm considering leaving the layout as is, 4 5000Ks and 14 2700Ks at a 3.5:1 ratio. I can use my T5 panels to veg and use the LEDs for flower.