DIY LED lights

[ALToronto]

Has anyone here taken a bunch of individual diodes and connected them to make a light fixture? I'm planning on doing just that, for a totally custom-shape, thin profile fixture.

As much as I love Ray's lights, I'm making a plant stand for seedlings where neither screw-in lightbulbs, nor 4' tubes, will fit. So I've placed an inquiry with a Chinese (what else!) LED manufacturer for some high-power (3 W) diodes in daylight white, bright white, red and blue. I'm waiting to hear back on pricing, but I get the feeling that these will be by far the least expensive solution per lumen output.

I plan to combine the different colours into strips and/or panels of about 40-50 W total power input. If anyone has played with these, I would appreciate some advice. I plan to order the following:

6500 - 8000K, white, 3W
5000K, white, 3W
430 nm blue, 1W
660 nm red, 1W
50 W drivers

Am I on the right track? Have I missed anything?

[naoki]

If you are going for the initial cost, did you consider chip-on-board (COB) type? Here is an example:

https://www.circuitsathome.com/diy-2...ht-a-build-log

The web page uses Cree CXA, but I just got cheap 30W cool white + driver for $9 (from ebay). I'm going to use CPU heatsinks from old computers.

If you are going for individual diodes, you don't need blue. Most whites are blue diodes + phosphor, right? Especially higher K diodes have lots of blue.

For the white, Table 1 and Fig 8 of this:
http://cpl.usu.edu/files/publication...b__2576523.pdf
may be interesting. But I don't know which color of white has the high PPF/W (I think cooler ones have higher lumen/W).

One of the well-regarded LED grow light makers announced that they are going with 100% white next year (they used to make R+B, then W+R before this).

[ALToronto]

Thanks Naoki. I'll nix the blue, but I think I'll keep the red. I might get far red instead though, in the 730 nm range.

I'm getting individual diodes - I need the thickness of the light fixture to be no more than 1/2". This way I can mount the driver some distance away and not have to deal with the extra thickness.

[naoki]

Oh, OK. Can you get sufficient heat sink for such low profile fixture? Thickness of COB emitters aren't so different, but I guess that it would be tough to get thin heatsinks for COB.

Let us know how the build will go!

[DavidCampen]

What are you going to use for the driver; constant voltage or constant current? What are you going to use for the heat sink? The drivers and heat sinks will cost as much or more than the LEDs.

[ALToronto]

David, the manufacturer I contacted also sells compatible drivers, but in any event, since I'm connecting the diodes in series, it would have to be constant current, no? Also, I'm buying diodes with heat sinks attached, I will mount them on aluminum plates, and I will put in fans to provide additional cooling.

I've put diodes together before, so I somewhat know what I'm doing, but thanks for raising these points.

[DavidCampen]

Originally Posted by ALToronto

David, the manufacturer I contacted also sells compatible drivers, but in any event, since I'm connecting the diodes in series, it would have to be constant current, no?

Yes, constant current would be most the most appropriate type of driver when each driver is supplying a single series LED string. I was curious if you knew that there are different types of drivers. You can also use various other configurations of either constant voltage or constant current drivers with combinations of either or both series and parallel strings but constant current is the most appropriate for your application.

[naoki]

David, if it's not too much trouble, do you have some pointers to various configurations? I'm only familiar with constant current with serial diodes, so I'd like to learn about the others.

Sounds like it is really difficult to get 1/2" profile with active cooling, Alla.

[ALToronto]

All the diodes will be exposed, so I don't think it will be as bad as enclosing them in a covered fixture. And the backer plate will be one big heat sink. It will have some air space behind it.

I got the reply from the diode manufacturer - they're making single diodes up to 500 W! No, it's not a typo. So I think I'm going to go with 5W diodes rather than 3W, since they seem to produce more lumens/W than the low-power ones. When I fist started playing with LEDs in 2005, 1W was considered high power. And I was paying $20/diode. Unbelievable.

David, thanks for reminding me about the different configurations. My old supplier did mention that the best way to configure a string of LEDs was in series, with a constant current driver (since LEDs fail by shorting out), and he'd been supplying me with cc drivers. Now that he's no longer in business, it helps to remember that I need to specify the configuration.

[DavidCampen]

Originally Posted by ALToronto

I got the reply from the diode manufacturer - they're making single diodes up to 500 W! No, it's not a typo. .

I am skeptical.

I use these LEDs:
LED Engin
Reds can be driven at about 10 watts and blue and white at 15 watts but each package is actually a cluster of 4 diodes. I buy then surface mounted on a Metal Clad Printed Circuit Board (MCPCB) with the 4 LED chips already configured in series. You can buy them from Mouser for around $10 - $15 in single unit quantities.