Quote Originally Posted by David Brown View Post
do LEDs produce (less) heat (than) tungsten,
Yes, if I understand correctly.

Quote Originally Posted by David Brown View Post
and do they damage relay circuits?
Maybe, see below:

Quote Originally Posted by David Brown View Post
Does it make a difference if the relays are mechanical or electronic?
Thanks, everyone. This has been interesting and informative. Allow me to narrow the follow-up question:

Regarding the relays: I doubt much of anything would be damaged in an old TIme-O-Lite enlarger timer. It's basically the same as a light switch. However, what I would be concerned about is my RH Designs Stop Clock (APUG sponsor alert). I don't want to fry its electronics with the wrong type of bulb, if that's possible. I am going to email the company and ask specifically, but it would be interesting to hear actual field experience, if there is any.