Gonna try this nifty little inline PWM dimmer, it's for brushed motors, but I don't see any reason it won't work on LEDs (PEMENOL Motor Speed Controller PWM DC 5V 12V 24V 150W Adjustable Speed Regulator with Stepless Variable Rotary Switch PWM Signal Generator Driver Module):
Total for all that (and ten 5.5mm power connector sets) was about $60. Sure, I can buy two basic LED aquarium light units for $5 more, BUT where's the fun in THAT? LOL
There are fancier/better/cheaper/more efficient items available, but these seemed to be good matches for my budget and needs (as I currently understand them) as well as they had specs I could determine.
Aside from the little "odds and ends" like hookup wire, solder, glue, screws, etc. (most of which I already have) the two main remaining pieces of the lighting puzzle are the "body" of the light (details TBD) and the mount (1/2" or 3/4" PVC frame, painted black, mounted to the stand... already know how this is gonna work.)
I'm planning on two units making up the light, one at the front and one at the back, which is required to avoid nasty shadows from the big black hinge strip running down the middle of the glass lid. Each half will have 2 runs of white and one red, about 30 inches long, for a grand total of 12 feet/4 meters of white and 6 feet/2 meters of red. I'll likely make each half tiltable, to keep the light within the confines of the tank. We'll see how that goes.
Aluminum extrusions have gotten so danged expensive! I'm trying to figure out something inexpensive to act as a heatsink/light mount, yet be visually acceptable... or which can be mounted within something that is. I have a few ideas, will report back when I actually build something. Also need to source an inexpensive clear cover for the lights, as plexiglass is really pricey now too.
Anyway, hope to have more soon. Good to finally be doing something other than overanalyzing and fretting. Worst case, I'll learn what doesn't work... that worked for Thomas Edison, so....
I have built loads of LED fixtures for tanks ranging from 10 gallon on up to 120 gallons. With LED lights for a planted tank the first thing to scrap is any measuring of lumens. the reason is you can build a LED fixture for your 40 gallon with 20,000 lumens and it is inadequate or with 400 lumens and it is over kill. The point being you need the right wavelengths for the plants rather the amount of visual light. I used to build my fixtures with a combination of warm white (3,500K) and daylight (6,500K) leds to get a balance. But I found to get enough light you had an extremely bright system.
My new approach is firstlook at the balanceo f light for the major photosynthesis frequencies which is basically red and blue LEDS. For a 40 breeder tank I d go with about 8 watts of "royal blue" leds and 6 watts of "red" LED's. This would produce the major photosynthesis the plants need. However your tank will look purple and many minor areas photosynthesis will be low on light. It only takes a small amount of neutral white (5,000K) leds to fill that gap. for photosynthesis. But to wash out the purple hue there is lot of personal preference involved so to be pleasing to your eyes you need something from the minimum of about 6 watts to up to an 24 watts of white LED's to create a pleasing combination to your eyes.
the end fixture would be someplace between 20 watts and 38 watts of LED's. I prefer using the Cree leds that can handle up to 5 watts each but running them at a around 2 watts each for more efficiency (light per watt uf power used),