I've had a LED fixture in the works for several months. I had the time to look through the forum here yesterday and realized several others are done with or part way through the process as well.
The following is my work so far along with some comparison pictures. Once fully completed I will follow up with more pictures and a parts list.
First of all, why am I doing this? I wanted to replace a 16 inch florescent fixture. With the exception of Catalina Aquarium, no one makes stock lights in this width. Thus, time to DIY it. When it comes to the question of florescent vs LED, LED wins because its way cooler, more fun to build, and the parts came at little to no cost to me. Without that last one I would have built my own 18 W compact florescent fixture due to the cost. Either way this fixture will need to fit into the plastic housing the old light came in.
Design questions? How many LED do you need? I gave up on trying to figure this out. There is not enough information to easily compare wattage on PC bulb to lumens from a LED array. In my opinion the problems comes in that lumens out of a PC bulb is measure in a way that collects light from all directions and directs it to a detector. This is not how we use PC bulbs in an aquarium though. A good reflector still has some loss in addition to light spilling out of the tank and restrike to the bulb. So you can compare diffrenet types of florescent bulbs but there are some assumptions that break down the comparison when moving to LED's. Light from a LED does not need to be reflected, and comparing power consumption (watts) breaks down because LED are more energy efficient.
In the end I just guessed how many LED's to get. I settled on 10 6500K 1W LED's at 55 lm each. I added 3 blue 1W LED at 11 lm each. The blue were to serve as a moon light but I am rethinking that now. More on that later.
Constant current Led drivers are the way to go. No need for resistors, they are flexible in terms of the number of LED's they can drive, are dimmable on the fly and if you blow a led to an open circuit the driver still supplies the same current. I am driving these LED's with 2 LuxDrive Boost pucks.
Now to some pictures. Forgive the soldering, I'm a chemist not an electrical engineer.
13" extruded Heatsink. These LEDs generate a fair bit of heat. Over the course of an hour the heatsink will become warm to the touch. When installed in the housing there will be two small fans moving air across this.
The business side
The LEDs are arranged (from left to right) a blue led, a cluster of 5 white, another blue, another cluster of 5 white and then a final blue. Each color is arranged in series 3 and 10 LED's long respectively.