Why are my seedlings so leggy when they get enough light?

Hey, a little bit of stretching is normal under SanLight LEDs as they emit not so much blue but more red in their light spectrum. If it really would have been 10cm long by now without adding soil on top, you may have had the light a little too far away for the first 2-3 days...it should be fine now with the adjustments and start to make bigger leaves while slowly getting bigger with the stem thickening. A good indicator is the color of the stems, they shouldnt be too light in colour, thats when you dont have enough light. Good luck!