Quote Originally Posted by mgb74 View Post
......As I understand, the standard Thomas-supplied bulb is 35w. I don't know if the Thomas bulb is proprietary (wouldn't think so but who knows). This site shows a number of sodium vapor bulbs with what I understand is the proper base, including an 18w:

Any experience with using a different bulb?.....
I purchased that 18w bulb--it does work in the Thomas (no, the Thomas bulb does not have a proprietary base), and I'm still using it almost one year later. But I didn't notice much difference on the light output. It was still too bright without cardboard shields covering about half the opening.