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DIY LED fixture for 20g long!!

917 Views 4 Replies 3 Participants Last post by  BigMek
Good evening everyone!

Making my own LED fixture is a very appealing idea that I would like to pursue. I've spent the past 24 hours (at least) learning the basics of how LEDs work and looking at the variations of DIY projects. Right now my top two concerns are:

  • How do I figure out the number of LEDs needed for a PAR of 45-50 at my substrate level (10").
  • What is the ideal heatsink to use for my application.

I'm not quite sure what LED brand would be efficient. I know the CREE XP-E come in a wide arrange of colors, and that the Bridgelux Vero 18 LEDs has a high CRI.

I don't mind the thought of soldering, however I do like the idea of bolting the LED stars to the heatsink so that in the futrue I can replace any burnt out LEDs. Any ideas/suggestions of heatsinks that would allow this would be excellent! I do know of the makersled but I need 30" which is very costly. I don't necessarily mind the cost if its really that worth it, but if there are other heatsinks that are similar and not so expensive, it would be ideal.

Thank you in advance!
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I think that 30" Heat sink on a 20 maybe overkill. depending on how you plan to suspend or mount the light, I think a 12" Makers Heat sink would be more than adequate. The 12" kit should be good for up to 100 watts, and you don't need anywhere near that amount of power on a tank of that size. Bolt in the leds of your choice and be done with it. Even if you go over board on the led count or power level, a dimming controller can be used to dial in just the right amount of PAR.
I've recently done two DIY LED arrays (working on two more) and have been helping Sean W. with his so I'll happily share what I've learned. I went with some el cheapo 1W LEDs off Ebay - link below - and decided to use 1.2 Watts Per Gallon of LEDs. Yes I know WPG is outdated and useless, but I couldn't find any decent guidelines so I guessed and it worked. Unfortunately I don't have access to a PAR meter, but using a lux meter app on my phone I hit something like 2,000 lux at 14" through air. According to another thread here that gives me an estimated PAR of 28 at substrate level (Lux divided by 70 is approximate PAR) so you would probably need about half again as much LED power, so about 36 watts on a 20 gallon.

Ebay link if it works: [Ebay Link Removed] 3W 5W High Power Red/Green/Royal Blue/Blue/White LED Bulb With 20mm Star PCB | eBay[/url]

One thing to keep in mind when going with a DIY fixture is to cover as much of the useful spectrum as possible. I used a combination of Cool (6500k), Natural (4500k) and Warm (3500k) white LEDs as well as Royal Blue (450nm) and Red (620nm) to make sure I didn't have any holes in my spectrum. I made my own heatsink (access to a bunch of tools at the makerspace I work at) but it's basically aluminum u-channel with a bunch of slots cut to make fins. With a good thermal paste under the LEDs (I used Arctic Silver) they stay nice and cool and the heatsinks only get about ten degrees above ambient temperature. Edit: This is a passive cooling setup. No fans! :D

I'll put a link to the thread Sean W. started about his DIY array. A lot of it is focused on power supplies but there's some good reading there.
http://www.plantedtank.net/forums/20-diy/1106370-need-help-driving-70-1w-cree-smd-leds.html
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I think that 30" Heat sink on a 20 maybe overkill. depending on how you plan to suspend or mount the light, I think a 12" Makers Heat sink would be more than adequate. The 12" kit should be good for up to 100 watts, and you don't need anywhere near that amount of power on a tank of that size. Bolt in the leds of your choice and be done with it. Even if you go over board on the led count or power level, a dimming controller can be used to dial in just the right amount of PAR.
I plan on putting it right on my glass top. Is a 12" heatsink enough for a tank that's 30"L/12.5"D/12.7"H? If that's the case then I definitely won't have to worry about its cost!

Bump:
I've recently done two DIY LED arrays (working on two more) and have been helping Sean W. with his so I'll happily share what I've learned. I went with some el cheapo 1W LEDs off Ebay - link below - and decided to use 1.2 Watts Per Gallon of LEDs. Yes I know WPG is outdated and useless, but I couldn't find any decent guidelines so I guessed and it worked. Unfortunately I don't have access to a PAR meter, but using a lux meter app on my phone I hit something like 2,000 lux at 14" through air. According to another thread here that gives me an estimated PAR of 28 at substrate level (Lux divided by 70 is approximate PAR) so you would probably need about half again as much LED power, so about 36 watts on a 20 gallon.

Ebay link if it works: [Ebay Link Removed] 3W 5W High Power Red/Green/Royal Blue/Blue/White LED Bulb With 20mm Star PCB | eBay[/url]

One thing to keep in mind when going with a DIY fixture is to cover as much of the useful spectrum as possible. I used a combination of Cool (6500k), Natural (4500k) and Warm (3500k) white LEDs as well as Royal Blue (450nm) and Red (620nm) to make sure I didn't have any holes in my spectrum. I made my own heatsink (access to a bunch of tools at the makerspace I work at) but it's basically aluminum u-channel with a bunch of slots cut to make fins. With a good thermal paste under the LEDs (I used Arctic Silver) they stay nice and cool and the heatsinks only get about ten degrees above ambient temperature. Edit: This is a passive cooling setup. No fans! :D

I'll put a link to the thread Sean W. started about his DIY array. A lot of it is focused on power supplies but there's some good reading there.
http://www.plantedtank.net/forums/20-diy/1106370-need-help-driving-70-1w-cree-smd-leds.html
Awesome! I appreciate your suggestions. I know the DIY community is probably board to tears with all the diy led questions but I needed to find out the calculation for my own tank. Hadn't come a cross another 20g build. Most builds are either 55g+ or nano, so the specs are way different.

I'll definitely check out that thread as well as that new sticky!
I guess I forgot to mention, I haven't done a 20 yet. I was just extrapolating the needs of your tank from my own experience. I have a 10 and a 40 long, but I used the same general layout for the 20 and 30 gallon arrays I'm building. I'm only running a low tech setup though so getting super high light levels isn't a big priority for me. Getting good growth out of crypts and vals and my amazon sword has gotten quite bushy, but I also grow tons of algae. :(

Basically the thinking was 1.2 WPG = 2000 Lux @ 14 inches, approx 28 PAR. So for 45-50 PAR you'd need about half again as much light (3000 Lux ~ 42 PAR at 14 inches) which means 1.8 WPG, so 1.8 x 20 = 36. At the time I was measuring half the array on my 40 long so it's probably a fair estimation for a 20.

Your needs will probably vary somewhat since there's a big difference between 14 and 10 inches of water column. Also, my lights are mounted to my tank lid so I don't have any loss between the light and the water. If you can over-build a little and get a dimmable power supply that might be the way to go. That way you can balance your lights around any CO2/ferts/etc you're doing.
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