The "K" rating is actually the color spectrum of the bulb. 6500 K is best for seedlings. Lite is white, and not a harsh color. LEDs burn very cool, so cool that seedlings can grow to touch bulb and not be burned.
LEDs, last twice as long as CFLs, so with that, and there efficiency, they will more than defray the extra intial cost.
Coverage rate for all, is basically the size of reflector.