The Planted Tank Forum - View Single Post - DIY led lighting - have I got it right before purchasing
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Old 01-05-2013, 06:30 AM   #11
ced281
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Quote:
Originally Posted by -Az- View Post
cheers mate.

I'll do a little digging on the ratios.
I've written down in my notes that 1rb:1cw = 10000-12000k ( I haven't noted where I got that info from).
the addition of the extra cool whites (5000-8300k) should soften the effect. can anyone confirm if I've got this right?

I'll have a look at the cheap LEDs. from my understanding the crees put out more light using less energy ( thus meaning less driving power for each string or more LEDs)
as well as what you mentioned with the accurate wavelength peaks. if the led peaks at the wrong wavelength then it potentially could be useless to plants become purely mood lighting ( eg red (670nm) and far red (730nm which is outside PAR).
I think you're right about the generic LEDs being less efficient at converting watts to lumens than the crees. But I think you can partially work around that by buying the "high power" LEDs which are supposedly rated at 160+ lumens. Here are 3W LEDs from China which generate 170-190 lumens.

[Ebay Link Removed]

If you look at the specs for the Cree XP-G's their 5W LEDs generate 260 lumens at 700mA.

http://www.cree.com/~/media/Files/Cr...g/XLampXPG.pdf

Anyone know how to calculate the lumens per watts for these? Will a 5W Cree really run at 5W if you're only running at 700mA instead of it's max 1.5A?

From back in my high school days, P=IV so Power = Current * Voltage. I'm assuming that the voltage doesn't change for these guys so if you decrease current the power (wattage) should decrease proportionally.
> So the power consumption of a 5W Cree running at 700mA is closer to 2.3W.
> Which means the lumens per watt is ~113
> Whereas the lumens per watt of these "high-power" Chinese LEDs are ~60 (180lumens/3W)
> Which means the efficiency of the Crees is almost 2x!
Does that make sense???

Quote:
Originally Posted by -Az- View Post
thanks for doing that steve

there seems to be a lot of yellow and green in the spectrum (wasted energy?)

i'm still concerned with the kelvins ( in regards to penetration)

"It is also noteworthy that many "terrestrial plant lights" as well as many aquarium plant lights (often are lower in kelvin temperature) have more "red nanometer spikes" than higher kelvin 6500k, 10,000k & higher lamps.
The problem with these lights is that while all plants utilizing photosynthesis require the same essential ABCs of PAR (see the PAR section), the facts of light energy penetrating water requires higher kelvin (6500k +) be added to provide maximum PUR (see Useful light energy/PUR section). Aquatic Plants and corals have adapted/evolved to the natural light energy at certain depth of water and the misguided attempt to adapt these terrestrial plant lights is not going to be 100% effective as a light with more water penetrating blue & slightly lower red nm energy."
aquarium lighting by carl strohmeyer

I,m starting to think about adding some reds in strategic locations about the substrate
Some of the limitations of light penetration by lower wavelength colors can be somewhat dealt with by using more focused beams (who knows how much it can be avoided though).

Having greens and yellows can be argued to be "wasted" light because they don't aid in photosynthesis, but the more green and yellow light you send into the aquarium, the more those colors will shine off your plants and into your eyes.

I would be careful about having too many red likghts. I read somewhere (I think in the lighting sticky) that algae is better at utilizing red than blue light, so having high levels of red light without proper plant load could be conducive to algae blooms, etc.

More food for thought! Let us know what you're planning.

If I end up having more free time I might start up a thread documenting my DIY lighting for my DoAqua 90P tank. I just got my makersled fixtures and am waiting on my LEDs from China =]
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