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post #19 of (permalink) Old 06-15-2011, 02:26 AM
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Join Date: Aug 2010
Location: Wake Forest NC
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Originally Posted by BlueJack View Post
Quick question...I have two of those 12 smd led bulbs over my fluval edge. I think they're .25 watts each smd? I haven't been able to grow anything with those, even low light plants. They basically just have enough power to keep things alive but not growing. Why is that? I know it's because they aren't putting out enough light, but what's the difference between the .25 watt smd's and 1-3 watt smd?
Originally Posted by BlueJack View Post
^Added to above question. I know chlorophylls a, cē, and peridinin have a "sweet spot" for using Photosynthetically Active Radiation between 465nm-485nm. That is pretty much where LED's have a good drop off. Would this lack of PAR "spike" be a reason for my stunted growth?
I would recommend you start a fresh thread on this so that you can get more responses, but in a nutshell, here's my take on this.

*Those low output 1/4 watt LEDs are not nearly as efficient as better-brand 3-watt class LEDs (Cree, Luxeon, Bridgelux). That's part of the reason they aren't working for you.

*The low-output LEDs are also nowhere near the power (literally 12-20X less powerful, per LED) than the 3-w class. They just don't put out much light for plants. That's the other reason they aren't working for you.

Basically, they are just too dim unless you use massive numbers of them.

You mention the 460nm color spectrum (blue) but honestly most white LEDs I've graphed on a radiometer show a considerable spike in that exact region.
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