LIGHTING
Plants grow is two specific areas of wavelength. Blue for leafy and hardy growth and red for flowers and fruits.
For lighting Cree's XP-E2 were selected both for their high powered output and the desired wavelength. The XP-E2 is a 3 watt LED which is capable of handling 1 amp of current. 700 mA of current was selected because it gave slightly higher lumen output. It also would be cooler then running at 1 ampere so a smaller heat sink could be used.
Royal blue, red and white were selected based on their wavelengths. Royal blue was the lowest on the blue wavelengths being somewhere between 450-465 nm. Red was on the opposite side being somewhere between 620-630 nm. Finally a warm white was selected to even out the curve and give an overall full spectrum.
All images from Cree's datasheet on the XP-E2
Heating is a concern when it comes to LEDs. LEDs lose effeciency when they get hot especially red LEDs. A heat sink with 4.7°C/W was chosen to help dissipate the heat in an attempt to keep the junction temperature down. Since there is 700 mA coming into the 6 LED array we can calculate that there is roughly 11.83 watts that is going into the array. To err on the side of caution we will say that 70% of that is going to be heat.
After waiting for the temperature to stabilize we see that the star board that the LED sits on was at 52°C which was well below our very conservative estimate. From this we can look at any loss of lumens in the LEDs, specifically the reds.
Looking at the red curve we can see that we are only losing about 20% lumens from the red LEDs. This is acceptable given the sharp losses that the red LEDs exhibit.