I’ve started a prototype DIY LED project which is basically just a proof of concept to see if the idea is even feasible and if I like the end result.
So here is some background, when I started my 20g aquarium I put in some plants, mostly of the low light variety. The tank only has a single 18″ T8 florescent tube for a light which is most certainly low light. My wisteria, which is suppose to be a fast growing plant, is actually growing quite slowly. In the future I plan on having a 120g aquarium that wouldn’t be much better off for light, so I was worried I’d have to upgrade if I wanted to do anything spectacular with my tank. The problem though is a 48″ dual tube T8 fixture is quite expensive, over $100 expensive. Yuck!
As an Electrical Engineer by day, I began to think, you know, I could make my own LED light fixture! I cost the project out, and it’s reasonable. Cheaper than any commercially bought LED fixture for sure. The LEDs themselves are only $5 each and each one produces the same lumen rating as an 18″ T8 bulb. Now, before you go running off to buy out the store of these super cheap $5 LEDs know that there is a lot of other stuff you have to buy in addition to the LEDs to get them to work!
You need a heatsink (these high power LEDs get HOT!), thermal paste, an AC/DC power supply, a constant current source, something to mount all this to, a pcb to assemble your circuit on, a power switch, a power connector, and all the various mounting hardware. And when you’re done, it will not look pretty unless you spend a lot more on a nice looking enclosure (or are handy with woodworking/metalworking and can make one yourself). Now, me personally I don’t care about aesthetics, at least not on my prototype project.
So, without further blabbing I’ll show some photos of the project so far. It is still a work in progress. This first photo shows you the LED itself mounted onto a blank anodized aluminum heat sink. Ignore the screws with their heads broken off. Pretend they don’t exists… and ignore the bad solder job, I learned the hard way to solder before attaching to the heat sink next time ;) If you don’t understand why, it’s because you need high heat to melt the solder, which comes from the soldering iron. But if you have a huge heat sink attached … you guessed it, it is much harder to get it hot enough to melt the solder! Lesson learned, I’m an engineer, I work on theory and paper, not a tech who actually builds the stuff I design =)
The brightness of an LED is a function of the amount of current going through it. The higher the current, the brighter it is. However, the higher the current, the hotter it gets and the hotter it gets, the lower its lifespan. For this particular LED a current of 350 mA will produce an output of 685 lumens at a color temperature of 5665K, for comparison an 18″ T8 6500K fluorescent tube is 700 lumens.
The current however is variable on many things, it depends on the input voltage, it depends on the value of a current limiting resistor, and it depends on the temperature of everything. In short if you just used a current limiting resistor with a DC power supply you would not have a constant, predictable current and thus brightness among all your LED elements. To solve that, you need what is called a constant current source, and if you can’t guess what that does I can’t help you ;) Below is a picture of the circuit I build following directions online (why reinvent the wheel?). It is simple and fairly inexpensive to build, but is not all that efficient. I plan in the future to try making a much more efficient design, but it would require a custom PCB which is very expensive to do.
See, pretty simple, just two resistors, two transistors, and a zener diode.
Okay, enough talking, here it is in action. The first photo is a picture under the 8000K fluorescent light I have, and the second is the 5665K LED (only a single LED, I plan to have 2-3 of them). You can clearly see the difference in color spectrum, but brightness wise I’m impressed on what that single LED can do!
Feel free to leave comments with any questions! I know the number one thing people will want is a schematic… I’ll think about it, but that would require me to draw it up and I’m quite lazy ;)