Quoted from Aniraf:
Definitely not the sockets. Incandescent bulbs work great, and new LEDs of the same type are perfect. Removing one of the dim LEDs then moving it to another socket still results in a dim LED.
not sure this is true in all cases.
I have a paragon with those old style 44 sockets and they worked great with incandescent bulbs.
as soon as I stuck an led in there it kept flickering or dimming.
I replaced the socket with new ones, still the same...So I finally crimped the casing a little bit so there was better contact.
works great now. I've had the same thing happen with the 555 LED's, a lot of times you need to bend the contact out to the side so there is solid contact with the socket.