Great thread, maybe too passionate?
I can only chime in and discuss my research. So JIMO:
Color absorption in seawater is a fact, higher energy blue penetrates deeper and as a result, deep water corals have adapted to that spectrum. But the effect requires a much deeper water column than any of our tanks represent. You start loosing the warmer frequencies around 10' depending on the clarity of the water. Few home aquaria are this deep, so the effect is pretty meaningless. All frequencies penetrate just fine in a 3' deep tank. So we are dealing with evolution here. The colors the corals can absorb depends on the color of the symbiotic algae. That algae can change in most instances to adapt to whatever is available. Depending on flow and other effects, this can either go well for the coral, or badly.
As far as wattages, photons are photons. I disagree with X on one count that 1 watt LED's don't grow coral. That's too broad a statement. Depending on LED efficiency and lenses (if installed) the photon density can be reached with a series of 1 watt or 3 watt. Generally though, 3 watt emitters are later generation and more efficient. But read this:
These guys build a lot of fixtures.
"We source top-bin LEDs from some of the best/largest LED manufacturers in the world. You are correct....it is not the LED wattage that is important. Remember, we are not lighting our tank with electrical watts, but rather radiometric watts. Hence, we tend to focus on 1) how much light the LED produces, 2) how efficiently the LED produces the light, 3) the lifetime reliability rating of the LED and 4) the cost of the LED. These are all very important considerations for building high quality, low cost lighting systems. We are continually evaluating LEDs from various companies, as we will only use the products that allow us to meet the above design considerations.
Here is a brief summary of the 1W vs 3W question I posted on the site last week:
We use both 1W and 3W LEDs in our fixtures. However, we believe the industry is too focused on the wattage of the LEDs. Alternatively, consumers should be looking at the Delivered Efficiency Rating (DER) of an LED lighting system. This is calculated by dividing the amount of light output that reaches the intended target (i.e. inside the aquarium) by the electrical input watts. This takes all of the marketing & hype out of the equation, and puts the focus on the metric that actually matters to consumers. As an analogy, focusing on the LED is synonymous to focusing on the engine of a car. By itself, it does nothing, and without a good drivetrain (i.e. optical and thermal management system in an LED fixture), a high performance engine will simply cause the customer to consume more gas than necessary to achieve highway speeds
In our design philosophy, the goal of an aquarium lighting system is to consume the fewest watts possible to deliver the required light levels with the best intensity and color uniformity ratios possible. Why use 140 watts if you can achieve this goal with 70 watts?"
So, yes, lower wattage LED's can be used as long as you remember the efficiency statements made above.
The color question is pretty complex as there are various factors, flow, placement, where the coral evolved and at what depth and what effect the spectrum you are using is having on the symbiotic population. That also controls how much total light they need during a day. Under high flow, they can take more, than at low flow. In general, they can grow just under blue light, but in many opinions that is not how we want to see them. As a underwater photographer I totted big lights down to the reef to add those warmer colors and get the corals to look natural, not just shades of blue. So the Reds and greens are more for us than the corals. A coral can get some benefit from even a red light but it may cause the algae to change (brown) to be more efficient at absorbing that warmer color, or if that color causes the coral to overproduce algae.
Halides grow corals, T5's grown corals, plasma grows corals and even natural sunlight (
can grow corals. LEDs certainly grow them as well when designed properly. Each to their own, I just find the advantages of LED now vastly outweighs the benefits of the other technologies in price and efficiency. I have had cheap fixtures that would only grow SPS if just inches away and I have had some that would grow coral from across the room. Color, efficiency, lensing and total radiological wattage is what determines the distance you can operate at and the amount of total PUR you can deliver to the coral over so many hours.
So everybody is right to a degree IMO. A crummy led fixture "can" perhaps grow SPS, it just depends on the distance, spectrum and duration.
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