I have some extra 1n4007 diodes, and was wondering whether, instead of using a power supply to drop the voltage, could I could power LEDs by just making a full wave rectifier, Using a capacitor to smooth out the power and powering n LEDs in series?
Here is the spec sheet: http://www.jameco.com/Jameco/Products/ProdDS/2095171.pdf
These LEDs are rated to go as high as 2.6V (red) or down to 1.9V. Could I create a series of 120/2.1 = 58 of them? With voltage going up as high as 128V, that's still 2.2V, well within spec.
This would mean that each LED would be less bright than maximum but would run cooler. Would that result in less efficiency? From the spec sheet, it looks like within a fairly large range, light output is pretty linear.
The current for this would be somewhere in the 20-30mA range. Aside from the potential for failure of one LED in series to kill the light, is this a reasonable hack? It seems to me that it's at least very efficient. The only losses I can see in this circuit would be in the diodes. I should see perhaps a 1V drop in the 1n4007?
Is there anything more efficient I can do?