to regulate circadian rhythm you want something that hits melanopsin, which is optimally excited at 484 nm. most LEDs have a gap in the spectrum there. like another commenter mentioned, waveform has some good products with engineered phosphors. they sell some reels of LED and heat sink channels which I used to make my SAD lamp. shitty ikea, costs a little more and you have to put it together yourself. still cheaper than off the shelf SAD lamps though