Why are LEDs so great despite having low wattage?

[jayjay5531]

e.g. I heard someone recommend 3-watts LED lights... how can that provide enough energy?
Other question: How does one ensure that the full spectrum of lighting is covered? are you supposed to use LEDs in conjunction with fluorescent bulbs?

 

[snakeblitz33]

Quote:
Originally Posted by jayjay5531 http:///t/395547/why-are-leds-so-great-despite-having-low-wattage#post_3521810
e.g. I heard someone recommend 3-watts LED lights... how can that provide enough energy?
Other question: How does one ensure that the full spectrum of lighting is covered? are you supposed to use LEDs in conjunction with fluorescent bulbs?
It's not the wattage that is significant.... it is the PAR value that is significant. PAR is Photosynthetically Active Radiation - it's a number that gives of the amount of actual useable "light" that is available to corals ... more specifically... to their zooxanthellae algae that lives symbiotically within their tissues. The algae makes glucose and the corals provide a safe haven for the algae to live. The land equivalent of say... lichens. (And for those science geeks out there, I know the difference between a cnidarian and a fungus.)
So, lets say that a metal halide that is 250 watts produces a PAR reading of 300 at the bottom of a 21" tank (roughly). An equivalent LED light that produces a PAR reading of 300 at 21" of depth can be only 80-120 watts, but still produce the same amount of PAR. (And for you technical geniuses out there, I just pulled those readings out of you know where, as an example.)
Full spectrum - well, that is where things can get a little tricky. Many people have been able to grow corals under blue and white light only successfully, but there are many out there that argue that these blue and white only LED systems make corals look really bland over time. I agree. Corals, for the most part, have adapted really well to using two ends of the spectrum - the first being blue light, which is one of the last light spectrums filtered out of the water at a deeper depth. Red is one of the first light spectrums to loose intensity with increasing depth, however, corals have adapted well to using only 10-15% of the red light that is available to them...
Now, saying this - what we as aquarists want, for the most part, is our tanks to look like a Dr. Seuss book. Full of color and life. To do that, we have to provide a full range of light to our corals, so that the zooxanthellae in their tissues can reflect back unusable color spectrums. For example, a red acropora does not process the color red - it reflects it. blue - blue and so on and so forth. If you want your greens to look green, your lights simply have to have the spectrum available for the algae to reflect.
As a side note, I have seen some tanks with those ultra royal blues and cool whites only, and I have found the corals colors quite lacking as well. It even made halimeda algae turn black - and halimeda algae to me is supposed to be a really pretty light green.

 

[jayjay5531]

Thanks so much for your detailed response! Is there any way I can check the PAR value of lights to compare, or is that info usually not available? Also, out of curiosity, what combination of lights do you use in your tank(s) (I'm assuming you have a full color spectrum based on what you said)

 

[heymybigfish]

very good read snake. i think i learn something everytime i read one of your posts...
but i have a question, i have the older style peg lights. (compact)... the bulbs are blue(actinic) and white (10k)...when i had my 1st reef tank set up, my corals were pretty ridiculous. i only had a few easy kinds (mushrooms, hammer, and zoos) but i had a pretty nice array of colors, green, blue, whitish-pink pale color, and orange.
so how did i have multi colors, only have a blue light? or is actinic, not technically a 'blue' light?

 

[snakeblitz33]

You can usually find par readings on forums if you do a search. But, you have to understand what a good par reading is before you know what your looking for. Read the lighting articles on reefkeeping magazine to get a better idea.
I currently have a four bulb t5ho system over my 75g tank. I am purchasing a reefbreeders photon48 this summer. It is a full spectrum led lighting system.
Florescent tubes and metal halides all have a wide spectrum of light they put out. Even though your bulb may say 10k daylight, it will contain a full spectrum and look white to your eyes. Over time a flourescent bulb looses its intensity and its spectrum also shifts to the red side of the spectrum. That is the main reason why you replace your bulbs every x number of months.
Leds on the other hand are light emitting diodes. And im not up to all the technical stuff, but they can be fine tuned within +-5-10nm (nanometers) which means that they lack a full spectrum of light that florescent bulbs have. White stays white, blue stays blue etc. thats the reason why people have been seeing bland colors with leds- is because they lack a full spectrum of light that makes corals pleasant for our own eyes to look at.