The best LEDs for plant growth are at about 430 nm and 680 nm. Blue 430 nm LEDs are very expensive $2-$3 a piece. Until I am ready to make refinements I am not willing to shell out those kinds of bucks. I am going to see if the 80-20 rule can be applied in this case, that is that 80% of your result can be achieved through 20% of your effort. The cheapest source of LEDs I have been able to find is from Jameco, they sell a one pound grab bag of LEDs for about 36 bucks, probably all red, green and yellow, a total of 1900 LEDs at about 2 cents a piece. I estimate that will create about an 84 Watt light panel, as I can afford it I will expand on it. Cheap sources of LEDs would be needed for such a project if you consider the large energy values involved, we're talking about replacing the sun here.
So, how many LEDs will it take? A 5 kW LED light panel is huge, 158 square feet. Gee, I wonder what an equivalent 20 year supply of sodium vapor lamps would cost? The power generating requirement would be greater too. Efficiency is the key to making the whole system work. To measure efficiency in the test reactor what one really needs is an sensor to measure oxygen generation. Otherwise one would have to spend a lot of time taking samples and doing chemistry, it will really slow things down.
LEDs are not characterized by light power output, but by luminous intensity, you can arrive at light power output by doing some calculations. A typical super bright LED I checked (I was not drinking) showed to be about 35% efficient. There are special high efficiency types that are even better than this, but cost more, the trick will be to tweak the design so we get the highest efficiency at the lowest cost. How does this compare to a sodium vapor lamp? Looks like a 400W sodium vapor lamp is about 21% efficient. By the way, blue LEDs are out, it appears that the typical efficiency for a blue LED is about 1%, the cost is prohibitive also.
Offered by Steve
Sharp produces Blue Led, High Luminosity Led, and Super High Luminosity Led, and others are Full Color LED Units, Chip LED, Laser, IR. Devices, and Fiber. There is a problem with discarding Blue LED's because they are very costly. Problem is according to the summary published by NASA in conjunction with several universities is Blue is essential to plant growth. Recommendation from that study is from 1% to 20% blue LED depending on plant and growth requirements.
Offered by John.