I don't know anything about the LED's and how they compare to fluorescent (you wouldn't use incandescent in any case).
But light intensity varies by the inverse square of the distance. That means if you have a light that is 6" away from the plant and you move it twice as far, to 12", the plants are now getting one quarter the light. If you move it four times as far, to two feet, the plants are now getting 1/16th the light. So a fluorescent that was 3 feet overhead would be doing next to no good. Does the LED give so much more light intensity to make up for this? I don't know.
Probably does depend on the LED. They come in a whole big price range from very cheap to very expensive. Last year I tried some LEDs for seed starting. They were the kind that look just like fluorescent tubes and they were the very cheap ones (me being me
). And they did nothing. My plants sprouted, but then just sat there. I have seen other people say the same thing. Not saying LED's don't work, just that there are a lot of different LED's and it helps to have some idea of what you are doing.
This year I went back to the fluorescent tubes I am used to. Everything else about the set up is the same. So far anyway my little seedlings are doing fine.