The brightness of the clock was about the same as a tired old VFD that has consumed most of its phosphor but this was something much simpler and something anyone could figure out how it worked once they saw the insides. The general look was closer to the nixie tubes the other commenter mentioned but these grids did not emit the light, the light source was a standard bayonet base bulb or two behind the mechanism. I think the smoked plastic on the front was also part of how it worked, it acted as a filter and without it you saw everything but the numbers you wanted to see.

Might have to go dig into that box in the garage and see if I still have it. I had intended on making a stand alone clock from it; the radio is not very good and the case has seen better days, so I was going to make a case for just the clock mechanism, perhaps its time.