Designing and Building a LED Fixture

[Hoppy]

Originally Posted by evilc66

You're not kidding. It's taken me about a year and a half to get all the intricacies straight for reef lighting with the use of two colors of LEDs, and the different optics thrown into the mix. Throw that on top of the thermal and electrical requirements and you have the potential for quite a mess on your hands. It has been worth it though.

Those of us who do this have unique ways to relax after a day in the garage working on LEDs.

[evilc66]

Sometimes it feels that way. You have to admit, the results are worth it. I have to get started on my freshwater LED setup, but there is something very different appearance wise with LEDs over a reef. Some have described it as "high def", but either way it's difficult to describe. Was it the same for you when you fired it up over the tank?

[Hoppy]

Originally Posted by evilc66

Sometimes it feels that way. You have to admit, the results are worth it. I have to get started on my freshwater LED setup, but there is something very different appearance wise with LEDs over a reef. Some have described it as "high def", but either way it's difficult to describe. Was it the same for you when you fired it up over the tank?

The short time it ran before burning out the power supply, it fascinated me. The shimmering shadow look on the substrate was almost hypnotic, to the point that I couldn't decide if I liked it or not. Then, I ran to get my camera, and when I got back the lights were off. I'm looking forward to getting a longer time to enjoy and study it next time, hopefully before this week is over.

I have tested each LED with about 200 mA current, using a 10 volt DC adapter with 30 ohms in series, low current, in other words, and the brightness is still awesome. I just touch the solder pads and it flashes like a photoflash. It flashes because I wince at the brightness, losing contact with the pads. These things seem like witchcraft, they are so intense. All of that light from an almost invisible point!

[evilc66]

Looks like another project to add to the list. One of these days the list is going to get smaller instead of bigger

[original kuhli]

Hoppy, have been watching this thread for a long time...kudo's to you for helping the community learn to 'do it on the cheap'. Your frustrations will pay off!

[Hoppy]

Originally Posted by original kuhli

Hoppy, have been watching this thread for a long time...kudo's to you for helping the community learn to 'do it on the cheap'. Your frustrations will pay off!

Thank you, I'm glad it has been helpful. Now, if only we could help DealExtreme row that canoe across the Pacific

[Cactus Bastard]

Originally Posted by Hoppy

The short time it ran before burning out the power supply, it fascinated me. The shimmering shadow look on the substrate was almost hypnotic, to the point that I couldn't decide if I liked it or not.

I put a single P7 on top of a 10 gallon, and found the shimmering to be a little overbearing. I think on a larger tank, with multiple light sources it wouldn't be as intense. Also the ten gallon, it was really high frequency, since the ripples had so little surface area.

[Hoppy]

I keep my water surface well rippled by directing a Koralia powerhead slightly upward. I'm a little bit anxious about whether that will produce a dizzying shimmer on the substrate. If so, I suppose I can reduce the ripple a little bit.

[Hoppy]

The replacement LEDs arrived yesterday, but it was much too hot to work in the garage, so I installed them this morning. The photo is with the current at about 200 mAmps. So bright it still dazzles my eyes 30 minutes later. I hope to get this back over the tank this afternoon to take some PAR measurements, see how much shimmer I get, and most critical of all, see if it will run all day. Wish me luck!

[CL]

Nice thread hoppy!
If the lights last this time, you might get a whole led movement going on pt.

[Regloh]

Originally Posted by clwatkins10

Nice thread hoppy!
If the lights last this time, you might get a whole led movement going on pt.

I'm on board... I think I have an opening for a new project the middle of 2011. Right after the controller, a new canopy, a second fish tank (in the office), the list goes on. But that's why we call it a hobby, right?

Looks really nice and bright hoppy. I can't wait to see the picture with it installed above the tank.

[Hoppy]

Running at 200 mAmps



Running at 400 mAmps

At 200 mAmps I measured 30 micromols PAR at 3" above the substrate, and at 400 mAmps, 45 micromols at the same location. At 200 mA I got about 45 micromols just below the water line, and at 400 mA I got about 100 micromols at that location, and about 80 micromols at about 4" below the water line. All of those measurements were in the middle of the tank.

The PAR remained constant just below the water line at about +/- 8 inches from the center going from end to end, and dropped in half right near the end. From front to back the PAR remained constant at about +/- 2" and gradually dropped to half at near the front and back. The plants kept me from making that type measurement further down in the tank.

At 400 mA I have about the PAR I was hoping for, possibly a bit low, but not much, and I can always lower the fixture a little to increase it. Right now the LEDs are 7 inches above the tank rim.

The shimmer is fascinating. Every leaf, every ripple and every fish casts multiple shadows on the substrate and the lower leaves. It is disconcerting at first, but in 30 minutes it didn't bother me. And, the light has been on about 30 miinutes now, with the heat sink not even feeling warm.

EDIT: The actual calculated current these are running at is 425 mA for each parallel string, or 850 mA total, for a total power consumption of 40 watts. The light intensity I'm getting is almost exactly what I was getting with a 55 watt GE9325K bulb in an AHS bright kit, mounted at the same location. So, this is using 73% of the power for the same amount of PAR.

Because the light is distributed over most of the footprint of the tank, and not coming from just a small area, the rise in intensity as you go up in the tank is not nearly an inverse square relationship, but is much closer to being linear. So, the intensity near the waterline isn't as high as I would expect from a typical aquarium light giving the same PAR at the substrate. (This is a good feature.)

It has been about an hour now, and the heatsink is still not even warm, and, of course, the lights are still working - a miracle!

[Minsc]

Good to see it working, it is an awesome light fixture!

What are your thoughts on the color of the lights?
Also, in case I missed it, how old was the PC bulb you tested?

[Hoppy]

These are cool white LEDs, giving a crisp white, which looks to me like a 10,000K bulb or something like that. I like it, but I also like the GE9325K light, for different reasons. The LEDs bring out the "neon" like spots on my new black phantom tetras, but don't emphasize the reds in the white cloud mountain minnows. I have found before that my eyes quickly see almost all lighting about the same, even though they have different spectra. The GE bulb is about 18 months or so old, so it is not as efficient as it was originally. I can't guess its actual age, since I have two of them and run only one at a time. The actual age may be closer to a year.

Two hours, and they are still working, and the heatsink still isn't even warm.

[Hoppy]

I can't see any "spot lighting" effect from the individual LEDs, so I decided to look for it photographically. Here is a normal photo looking down at the substrate:


I can't see any spotlighting on that, so I tried cutting down the exposure, jacking up the constrast, and cutting down the brightness, to see if that will reveal any spotlight effect:


Even with that, I can't see any spotlighting. From that I think it is safe to say that a 3 inch on centers spacing of the LEDs works very well, at a distance of 20 inches or so. Perhaps at half that distance it might show spotlighting, but I can't tell about that without making the water cloudy so it shows the cones of light from the LEDs.