Led q&a

Looking forward to any data you have. I'm very excited to here that man speak at MACNA. I think I'm looking forward to that as much as just being there. Once my build is done I'm going to break down and buy the Apogee MQ-200. It'll be a handy tool to have around. The hold up on my project is mainly due to the lack of data available on what matters most to aquarium applications. I don't want to spend 300-400 dollars on a light and still have to place all of my sps up high on the rocks. lol

 

Dang I was really hoping you had some data. Lack of it is my biggest concern and is why I haven't moved forward with my project.

 

Here is a setup that I was gonna add to my 225 build. It is made with Cree LEEs and I was going to have three sets made for each opening. I mean that fixture with one more set of LEDs.

 

Reefmonkey, I know for a fact that the photons produced by LEDs are more linear than halide light so naturally LEDs will hold their PAR for longer until the photons start to loose their trajectory. For reference, fluorescent bulbs produce light that is not very linear at all and that is why it looses it's PAR much faster than halides and LEDs do

 

Cool this is the kind of stuff I'm after. I'm not trying to disprove anybody, there's just no data readily available that is very helpful for use when it come's to growing and sustaining corals. I really would like to know a lot more about LED's before I commit to building a fixture.

 

Great questions you have here Steve, thank you for asking! here are the answers:
1. PAR is surprisingly high with LEDs, comparable to halides. The photon trajectory is very linear so the PAR levels remain high at deeper depths than what was previously achieved by MH bulbs. The spectral output of LEDs is very controlled and this is great for us because it means that nearly 100% of the PAR released from the diode can be translated to PUR... None is lost as UV radiation (which can still be used by most sps) and very little is lost as infrared radiation (above the red wavelength). When you get into the specific colors (blue, red) they only emit a VERY narrow range of wavelengths so the color you see is the only color being released. The levels of PAR are very comparable, if not slightly better than the very best of both t5 and MH lighting.

2. Cree has taken an obvious role as the forerunner in LED lighting... their values for lumens per watt are beyond anyone else! another brand worth mentioning is Luxeon. Cree comes out with a new LED every couple of months so the standard is constantly being set higher.

3./4. This is a function of the types of lens you use on your LEDs and how hard you drive them. The lens will direct the beam from 100-120 degrees to a smaller radius such as 60 degrees. this actually causes the PAR in the center of the field to be drastically higher than that of the outside... the formula for dissipation of lumens for a lens closely resembles a normal distribution curve, whereas the loss in lumens can be calculated in standard deviations from the center (calculus, and i dont think anyone of us wants to go there right now). LEDs can be driven at different amperages. This is done by a driver that can either be constant or variable (variable is ability to dim). Typical values are between 300 mA and on the most cutting edge, 1300 mA... With an average at about 700 mA. The lower the amperage, the less light put out and the longer the life... the higher the amperage, the more light and less lifespan. At 700 mA LEDs are in a very happy medium between output and lifespan (50,000 hours).
In order to avoid shadowing you can switch out the type of lens for a more broad or narrow one, or you can elevate the LEDs higher above your tank to get more uniform distribution.

If im not mistaken, the formula to solve for diameter of a beam is:
tan(degrees of optic) * (distance from LED to sandbed) = (diameter of beam)

Thank you Steve