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Algae use mostly deep red 660nm light. Not much blue, and no green. The reason for this is because algae (unlike trees) grow underwater. And guess what color water filters out the most? Red.

If you go down a few meters in a reef, it gets blue quickly. This is because the red light is removed quickly by the water; then the green is removed. This leaves blue light to go deep. But where does algae grow the most? At the surface, especially on rocks where waves are crashing. Algae can actually drill down into the rocks so that attachment can be made, and thus not washed away. This is how much the algae prefer red light, especially with turbulent air/water (and rocks) at the surface. So why not make all scrubbers with just red lights?

Well, LED lights come in many colors, and for scrubbers the main colors currently used are red, pink or white. Red light grows the most algae, followed by pink (which is red+blue), followed by white. White light, however, poses a problem. White light, especially from white LEDs, has very little red light in it. "Cool" white light has almost no red light; even "warm" white LEDs do not have much red. Compared to a pure red 660nm deep red LED light that has 10 watts of real light (which is maybe 20 watts consumed at the power plug), a white LED light would need at least twice this wattage to grow the same amount of algae, and probably more like three times the wattage. So why would you use white light if you could instead just use the red or pink that algae prefer? Because of glow.

Glow occurs when a light is used inside of a non-black case. A white case, especially, produces the most glow. Since light travels easily through white plastic, especially acrylic, light inside of a white case can glow enough to illuminate a room at night. This is why you would not want a better-growing and lower-wattage red light in a white case, because it would illuminate the room or cabinet a red color and would look like an airport beacon. So, you choose a white light. But this requires 2 to 3 times the wattage (and heat).

Although a 30 watt white LED light (compared to 10 watt red) does not sound like a lot of extra power, is can be a lot of heat, especially if there are 2 or 4 of these lights on a scrubber, and especially if the power supply for the light is on the inside of the light instead of in a separate power supply box near the power plug. And also if the scrubber is in an enclosed sump cabinet area. There additionally is a safety issue with lights that have the power supply inside the light; see our for details.

Enter the black case. Black plastic blocks all light, so you can use as much red light as you want and it will be not travel through the case at all. The only light which escapes is through small openings needed for operation. So with red, you can reduce your operating wattage (and heat) to 1/2 or 1/3 and get the same growth. Some people think the red has a pleasing feel too, like a deep sunset.

An interesting thought, is that 660nm deep red is the same color used for "red light skin therapy" in spa salons, and it's the same color as fully oxygenated blood. And don't forget that the growth can be used for skin therapy itself, by putting it in a warm wet towel on your skin. Multi-algae fun!