LED's talk about LED
LED's are a very unique source of light. And before building up this daylight simulator, it's better to take note of the pro's and cons of them....
Off course there are different kind of LED's with all their own characteristics. The LED's I am talking about are RGB LED's, and more specific: the ones sold as LED strips.
The quality of light
As RGB LED's are actual 3 LED's in one housing, they do not really produce white light: they blend red, green and blue to create the desired color. These three colors are rather pure: their spectrum is small. On the left side, the spectrum of an RGB LED, right the spectrum of a light tube for fish tanks. The white line in both spectra shows the spectrum which is needed for photosynthesis.
Blending the light with an RGB controller cannot fill-up the gaps: Parts of the spectrum which are absent cannot be repaired. The TL on the right does a better job, although it's also not perfect. So, if your tank contains plants which need of good light, you can consider using tube lights for at least a couple of hours a day.
I want to use LED's for saving electricity
On the web, you can find manufacturers with nice stories about high efficiency, lots of light... The small RGB LED's on strip do not have a high rate of efficiency, and the promised light output may be a little lower. The movie of my tank is made with 300 RGB LED's on a strip, of the type WS2812 IC 5050 RGB LED, with the specs below:
|Red||620-630 nm||550-700 mcd||20 mA||2.0 V||40 mW|
|Green||515-530 nm||1100-1400 mcd||20 mA||3.1 V||62 mW|
|Blue||465-475 nm||200-400 mcd||20 mA||3.3 V||66 mW|
As my white point seems to be red: 100%, green: 71%, and blue: 35%, every LED uses 40 + 44 + 23 = 107 milliwatt. For all LED's together, we are talking about 32 Watt. And the level of light is definitely below the light of one 18-watt TL.
I want to use LED's for saving money
The lifespan of a LED is very long. But actually, lifespan is the wrong term. Most of the time, LED's do not stop working, they just shine less bright. Technically they are not broken, and their lifespan hasn't ended yet. But still they become unusable. The picture shows two led strips (not RGB, white LED strips). One is unused, the other has been used for about 10.000 hours (3 years).
Nowadays, LED's become cheaper and cheaper. But for this project, you need some things more, all with their own lifespan. And as I mentioned above, you won't save money on electricity either, I guess.
LED systems like this have the advantage like all DIY projects that they have a high rate of replaceability: one thing damaged, one thing replaced. My old light hood of the tank was made for tube light, and had its starter unit sealed in. Unreplaceable. Therefore, a broken starter-unit charged me for almost $ 80.00.
Other points about LED's
As I am a DIY person and not a high skilled electrician, I prefer the fact that my light hood only uses 5 Volts. (or 12 Volts, depending on the kind of strips) Besides that, I also like the fact that the temperature in the hood does not raise to destructive levels anymore. And off course the biggest advantage: the customizable colors. Even if you use a standard RGB controller and 5-10 meters of strip with no color changing at all: you can change the appearance of your tank with one button press. With tubes and other lightsources you even get surprised when you first light them and the color is a little "different as expected", Get used to it, you will see that color for long times.
As most of the TL lights have the same efficiency, many tank-owners think about "watt per liter/gallon". Nowadays there are so many light sources with different specifications, that it becomes difficult to compare them. What about lux, lumen, candela and mcd? Take a look at the picture below. The red and white desk light have the same intensity of light, and blue and white have the same size of beam... So, all are different.
Talking about lux is talking about intensity. As you can see, the white and the red light have the same intensity. Because of its wider beam, red produces more light, but still has the same intensity. Therefore, Lux is impractical to determine the amount of light sources needed.
Candela is the luminous intensity in a given direction per steradian. In other words: the total amount of light within a certain direction (a steradian). This is actually also a quantity of light-intensity. In the picture, white and red have the same amount of Candela, blue has more.
One MCD (micro Candela) is 1/1000th of Candela.
Lumen tells you something about the total amount of light which emits from the light souce. In the example above, red and blue have the same amount of Lumen, white has a lower amount. The fact that blue has a smaller beam causes its beam to have a higher intensity. For your tank, you need to use the amount of lumen to decide the amount of light sources. It is possible to calculate lumen if you know candela or lux, as you also know the radiation angle of the source. Conversion can be done on many sites on the internet (click).