There are some that use phosphor and tritium filled tubes, and those will glow for about 20+ years before they get dim enough where you probably will want to replace it...the half-life of tritium is 7-years, so in 21-years, it would be about 1/8th the brightness of when new, but still visible (1/2 after 7, 1/4 after 14, and half that again at 21, or 1/8).
I have one with this from -
http://www.ballwatch.com/html5/index...k=1&lang=en_US . It's not very common, but you can find this tech on some others, but I think Ball does it best and with more of it than others. And, they have some designed by BMW with their logo, if you want this (I have a Fireman Stormchaser DLC Glow - not one of the BMW designs; I wanted more tubes!).
FWIW, wearing it 24/7, the radiation is equivalent of about 1/1000th of a chest x-ray in a year...you get FAR more in on one trip in an airplane.