As i mentioned in my previous log, i received led strips from china : http://www.aliexpress.com/snapshot/6379239770.html

I also have waterproof ones, but since they are molded into a silicon strip, i have yet to figure how to solder it. I thus started working with those ones. First of all, they are very bright. The strip is said to consume a bit under 9W per metter. For my smallest aquarium, i cut 3 strips of 45cm, so it should draw aproximately 12W. Each strip of 45cm produces more light than a fluocompact bulb. So here, i'll be increasing the light output and cut the power to less than 1/3 of the previous power usage.

Those strips use 12V DC, so for 1m, they use 0.75A, according to the specs. Here, i'll be using roughtly 1A of current. This is good, because i don't have to use thick wires, nor use beefy transistors. The plan here is to control the LED with a TIP120, driven by an µC pin.

I did try it, and it succeeded. I used an Arduino variant, and i could send PWM to the LED. It worked properly, effectively dimming the LED. They are easy to solder and to work with. A slight downside is that it is not a continuous strip : smaller strips have been soldered together to produce a 5m strip. It causes the strip to be slightly non flat on some bits, and it could be harder to cut if you want to cut exactly where is the solder. However, with a cutting tool it works without any problem. And the strips are really cheap (5-7$ including shipping... for 5 meters!).

If i can send PWM to the LEDs, it means that i can fade the light in, rather than brutally turn it on. I thus made fading functions, with the possibility to specify the total fade time. So now, if i send setLights1FadeIn:time through serial, the strips will fade in in "time" seconds. Without the time argument, it will fade for the duration stored on the chip. I obviously made the corresponding fadeout function. So now, rather than just turn the lights on or off, i will fade them in, in order to reduce the stress for the aquarium inhabitants. I can also now set the max luminosity, so i can adjust how bright the aquarium is lit.

At first, i considered using three relays to turn each light bulb on, to have a "sunrise", but now with the LED i can do it properly.

This first aquarium will thus have 3 strips of 9 packs of LED, each pack containing 3 LED, for a grand total of 81 LED.

According to the spec, i should have 40-55 lumen per LED. If i consider 30Lm per LED, that is still 2430Lm for my aquarium. The previous lights had a max of 800 lumen per bulb, but a significant part were wasted , despite of the reflectors. Here, the light is directed towards the water. Furthermore, i should have little to no light quality degradation over time. As an example, i just noticed that the middle bulb in my aquarium is dead, so less light.

If i consider 40Lm per LED, that's 3240Lm total, and if i consider 55, that's 4455Lm.

I know that the manufacturers often lie about the products, but it is also valid for light bulbs, so this values are a mean of comparison.

For now, i'll underestimate the light output of my system, and dim it if needs be, rather than overestimate, and have to add more LED. Plus i like 81, as it is a power of 3, which is cool, uh?

My second aquarium is 70cm long, and a bit higher. I'll thus use strips of 70cm or less (you have to cut after a pack of 3 LED).

Since it's higher, i'll increase the amount of LED strips (4 to 5). So if i use 65cm strips, that'll consume 5.85W (let's say 6W) per strip, and draw aproximately 0.5A per strip. I'll thus need 6*4=24W to 6*5=30 of power, draining 2-2.5A, still good for a TIP120.

I have 0.6 LED per cm, so i should have 39 LED per strip, producing a low estimate of ~1200Lm per strip, and according to spec, 1560-2145 Lm per strip, for a total low estimate of 4800-6000Lm, and an "spec" estimate of

6400-8580Lm for 4 strips, and 7800-10725Lm for 5 strips.

Considering those numbers, i may end up using only 3 strips, for 3600Lm low estimate, and 4680-6435Lm for "spec" estimate... Or simply use more and dim it if needs be.

More LED means a better light distribution, so why not, after all?