If they're miraculously a perfectly consistent Vf, determine how much current that 300 will use, wire them in parallel then drop that over the surplus voltage across high-power resistor(s) on the positive or negative leg.What is the best way to do this?
LED tape, fairy lights also potential options.Best or easiest? I would just buy a string of holiday lights.
What form does this take: what length, or multiple lengths; can you use ac power or use battery; how bright, and have you already acquired (the) LEDs? If yes to last point, specs of the LEDs?I would like to wire 300 blue LEDs to one power source in order to light up a tree. What is the best way to do this?
They are correct for 3mm, 5mm and 10mm leds, and i have done almost same thing (just less leds) with such leds more than once. since OP never mentioned what leds he had in mind, but did mention he is is about to wrap a tree with 300 of those, i assumed it would be cheap 3 5 or 10mm leds.Some of your numbers are off. Most small white LEDs are in the range of 2.6v to 3.2v at low current (say 5-10mA) etc. I worked on component 2nd-sourcing and went through this is detail.
In any case connecting LEDs directly across the line without proper current limiting is a bad idea, regardless of how you try to balance the voltages. Perhaps it worked for you, I do not recommend it.