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post #1 of 32 (permalink) Old 06-17-2011, 07:15 PM Thread Starter
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LED my way

Not sure where to start here, but I wanted to share in hopes that it may spark some ideas in others.

So, I have this 70 gallon bowfront corner tank that I've been planting since I got it some 8 years or so ago. I've always been disappointed with the light I was able to get into it due to the bulky frame design and complex footprint.


Long story short, after some trial and error and mostly unsatisfactory results using more conventional solutions, about six months ago I settled on designing and building a DIY LED fixture.

I had several goals.
-1st and foremost was to provide good color rendering and high PAR levels throughout the tank
-2nd, I wanted to save energy compared to the ~250 watts of power compact lighting I was using at the time.
-3rd, I wanted to reduce maint. cost in the form of bulb replacements.
-4th, I wanted to have the ability simulate a dawn/dusk effect.
-5th, I wanted to reduce the audible noise.
-6th, I wanted to reduce heat transfer into the water column.

Much more to follow...
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post #2 of 32 (permalink) Old 06-21-2011, 07:08 PM Thread Starter
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First thing I wanted to do was see what I needed to produce good color. My very first look was to use a philips 120v LED PAR38 spot to get an idea of color and number of LEDs/lumens I would ultimately need. This test showed that a cool white alone washed out the color of my fish (white cloud mountain minnows) but provided good general light and excellent shimmer.

After looking at various options, I decided to use the LedEngin white. I liked their glass primary optic, spectrum, factory-soldered star (reliable thermal data), and long lumen maint. projection.

After that, I ordered a selection of colors to span the entire visible spectrum.

I built a couple simple test rigs. The first was for a single star-mounted LED powered by C-cell batteries. The second was for 4 stars powered by a PC power supply and allowed dimming for each of the four channels so i could check color mixing. For the single, I used a large northbridge heatsink. For the 4-channel rig, I used a large CPU heatsink.

I tested the following colors:

365nm (ultraviolet)
400nm (ultraviolet)
460nm (royal blue)
490nm (baby blue)
505nm (cyan)
5500k (cool white)
4100k (neutral white)
660nm (deep red)
735nm (far red)

Both of the ultraviolets produced objectional flourescence of the particulates and/or organisms floating in the water column so I did some research to see how important that part of the spectrum was to both plants and fish. It seems that UV-A is not terribly important and may even be harmful, so I elected to discard that portion of the spectrum.

The royal blue, surprisingly to me, induced a fair amount of flourescence in my fish, but it was a redunant part of the spectrum. All the white LEDs have a spike in the 450nm range and adding this to a white was just way too blue.

The 490nm blue proved a bit too blue to properly fill the response valley of the LedEngin whites. The 505nm works good color-wise, but the viewing angle is darn near 180 degrees. A wide-angle (90) optic is required.

Based on spectrum data comparisons I've done, I suspect that the 490nm would pair up nicely with a Cree white LED since they appear to be a bit more biased toward the deeper blues.

The 660nm red is a true "fire engine red", not one of the more pale red-oranges commonly found and labeled as "red". It is also centered on a photosynthetic response peak and really adds a lot of punch both to PAR readings and my fish's red colors.

The 735nm red is pushing the edge of infa-red as you can feel the heat on your skin and the light produced is very dark red and quite dim. since this color is present in sunlight I decided to add it even though most articles I read indicated that it was responsible for stem elongation. I may reduce or remove this piece of the spectrum at a later time depending on plant response.

Comparing a Cree 4000 kelvin white to a LedEngin neutral white:
(the purple and red vertical lines indicate the practical limits of photosynthetically usable wavelengths. The light gray trace is a response curve of overcast natural daylight (6500k))


Estimated effect of adding colors to achieve more even resonse:
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post #3 of 32 (permalink) Old 06-21-2011, 09:41 PM Thread Starter
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Having settled on a color selection of neutral white, 505nm, 660nm, and 735nm, I had to start working on determining the number of LEDs I would need to achieve a high light level. Not having any real data to work from (at least none I knew of), I started at the beginning...

This meant answering a few basic questions... How bright is bright? How is brightness measured/reported?

Obviously, LED manufacturers generally report the brightness of their high power models in lumens. Turns out a lumen is a difficult unit to define, but it converts easliy to lux. Fortunately, lux is commonly used to measure brightness in everyday situations that I could relate to. BTW, 1 lux equals 1 lumen per square meter. I made all my subsequent calculations assuming the LED illuminated 1 square meter and adjusted based on the actual footprint of my tank.

Various sources cite direct sunlight as being between 10,000 and 500,000 lux.
I measured my old Orbit fixture at about 3000 lux (at about 30" in air).

I sorta split the difference and set my goal at 5000 lux (5000 lm/m)at the substrate.
The Neutral White LEDs I chose are rated at 200 lumens across an angle of 125, but since the light isn't distributed uniformely within that cone, it's only 170 lumens across a more managable angle of 85. At a distance of 28", that 85 illuminates an area of about 1.34m or 79lm/m (equal to 79 lux)

My tank footprint is about .464 m, which is about 1/3 of the above, so I would need almost 100 LEDs to reach my target.

NOT HAPPENING!

Looks like I need some secondary optics. Unfortunately, there's not a great selection of optics designed specifically for the LZ1. I didn't need (nor want) a spot and the broadest I could find was about 45...so be it... Taking into account reported optical loss, the reflector essentially mutiplies the intensity of the LED by 5 times. That brings me down to a more managable 20 LEDs.

I also didn't know how the refraction of the water column and glass would affect the light, but I knew I would gain intensity from it. 15 to 20 LEDs seemed a safe bet.

After playing with LED placement, I settled on 12 whites and 6 each of the colors. I know...12...what happened to 15-20? My total LED count is 30. The Cyan LEDs each supply about half as many lumens as a white and the reds are basically unknown since I didn't feel like trying to convert their output in milliwatts to lumens...suffice it to say that they are quite bright for red...but I was comfortable that I would overshoot my goal by a comfortable margin and still save on electricity.

A rendering of what I had calculated and what I was working around as far as the tank was concerned (notice the big frame gussets at the corners. This reflects the shape of the frame AFTER I had removed a significant amount of bracing):


front:


side:
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post #4 of 32 (permalink) Old 06-21-2011, 09:58 PM
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It looks like you put a lot of thought into this. I am looking forward to seeing how it all turns out in the end.

Just one thought... I think that if you come anywhere close to the intensity of natural sunlight you will have way too much light to control. I just don't think it is manageable in our tiny little ecosystems. I know you aren't aiming for that much, just sayin'.


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post #5 of 32 (permalink) Old 06-21-2011, 10:29 PM
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Guess what happens when those light cones hit the surface of the water.... I've yet to see a mock up that shows refraction at the air/water interface.
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post #6 of 32 (permalink) Old 06-21-2011, 10:48 PM Thread Starter
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I'm aware. You'll no doubt notice I also didn't include any refraction from the glass...but I did consider its effect and mentioned as much in the text. I don't have ray tracing software and modeling all that by hand is a royal PITA.

As far as my data is concerned...well this is hobby work. I'm doing it as much for the fun as anything. I like to learn and I like to build, but I'm only investing as much time in the details as I feel is necessary to achieve a positive outcome. Too much worry and the fun turns to work. Anyway, none of my luminance numbers used more than about 80% of the published total output of the emitter and even that data was culled from the middle bin and assumes running them at 1000mA. They are capable of running up to 1200, so if needed I could boost light output ~15% just by bumping up the current.

If I was ~really~ serious about this, I would have ponied up the dough for a PAR meter and done some real testing. (not saying I won't still do that...just to find out what I've really got...)
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post #7 of 32 (permalink) Old 06-22-2011, 08:35 PM Thread Starter
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That brings me to the point of figuring out how to mount and cool the LEDs.

I decided to use active cooling and a single fabricated "manifold". It uses air moving thru the inside to help cooling. My plan was to use a single blower pressurizing the manifold and exiting thru six outlets. Unfortunately, I couldn't find any blowers that were quiet enough. I was shooting for 30 dB or less. Ended up splitting the manfiold into two circuits and going with six small (40mm) fans. Four fans pressurize and two exhaust with an additional single passive exhaust.


1"x2" aluminum tube:



Airflow thru two circuits:
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post #8 of 32 (permalink) Old 06-22-2011, 08:43 PM
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Ahh... another struggle to light up a bowfront corner tank! I love my 54g bow corner, but wow it's hard to light that sucker up.



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post #9 of 32 (permalink) Old 06-22-2011, 08:45 PM Thread Starter
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Moving up the top level...this model shows all the LEDs and fans installed on the heatsink which in turn is installed on the...what? Cover? Lid? I dunno.





Side view:


...and just because I think it's a kinda cool rendering...a closeup of a cluster with the Boomerang installed:
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post #10 of 32 (permalink) Old 06-22-2011, 08:50 PM Thread Starter
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First fan plenum bent up...





Used to working on computers, this 40mm fan seemed awfully small compared to an 80mm.
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post #11 of 32 (permalink) Old 06-22-2011, 09:02 PM
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This is a great project. Thanks for documenting it. Can I make a suggestion?

Have you thought about trying to "aim" the front row of led's toward the back and vice cersa? I have played around with the idea some and find the effect to be noticably more appealing than direct overhead lighting. Kind of like when you go to the strip... local shakespeare theater.
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post #12 of 32 (permalink) Old 06-22-2011, 09:06 PM Thread Starter
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Good suggestion. I wish I had heard it a month ago.
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post #13 of 32 (permalink) Old 06-22-2011, 09:08 PM
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Nice nano ductwork!
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post #14 of 32 (permalink) Old 06-22-2011, 09:29 PM
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Very nice work! Are you running the wires inside the aluminum tube?


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post #15 of 32 (permalink) Old 06-22-2011, 10:15 PM Thread Starter
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I considered running them inside, but decided it wasn't worth the effort. It's all hidden behind the valence anyway.
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