how to fasten chip Led's to Lionel train cars, double stick tape, hot glue, blue tack?
Original Post
Yes. (Any or all of the above will be fine.)
Just make sure that if you're gluing down, or taping, to a conductive surface, e.g. metallic, that the electrical contacts that you've soldered wires to on the LED don't touch it.
If you need to insert an insulator between the chip and the surface please do so. (This could easily mean that you need to glue ir bond the chip to an insulator first, then glue or bond that assembly to the metallic or conductive structure next.)
Mike
