10 years ago
If you just wanted to do it once all you have to do is plug it in to a series of batteries (or any one battery) that hold(s) a charge greater than what the LED can support. However, I'm sure you could do this with a switch and a few transisters and resistors - do a search on Instructables and you ought to be able to find something.
once per switch throw would be good. going from dim to its full extreme brightness like a laser charging up(scifi space ship) I would thing the charge up time would run about 1.5sec no longer.
Just once? Or periodically? How long, in seconds, is the gradual turn-on period?
How gradually ? An R-C circuit, with a pair of transistors wired like a thyristor would do it.