How can I identify lights?

[NorthAlabamaTrains]

How do I know if they are LEDs or incandescent? Also, there specifics like size? Just from a quick inspection.
Thanks.

[freebrickproductions]

These pages should be of help:
http://www.rxrsignals.com/102/Light_Inserts/
http://www.rxrsignals.com/102/Signals/
(Note, for whatever reason, the second page uses flash images instead of .png images for the titles of the subpages, so you may have to tell your browser to run flash. I'll see about getting this fixed at some point in the future.)

Also, the easiest way to tell the difference between an LED and incandescent light is that incandescent lights generally "fade" on and off, while LEDs usually "snap" on and off. There are some LEDs that are designed to fade on and off, but they're also more of the "dotted" variety with a bunch of diodes across a breadboard, which looks very different from an incandescent light. Many LEDs, especially older ones, also have their lenses stick way out from the light-head, while most incandescents (and a fair number of LEDs) don't.

[NorthAlabamaTrains]

Thank you so much! That all makes sense. Also, just want to say, I love your channel. Keep up the good work.