I took in a old 50s Altimeter to work today, to use various instruments to see if there was any gamma radiation being emitted from it..
If the 50s instrument was not a gamma emitter then it wasn’t luminous in the first place. I can’t quote them from memory but the relevant half lifes are such that the time elapsed since the 1950s pales into insignificance.
Luminous instrument usually show a thick dark brown paint applied to only some of the numbers and letters. They are also ferocious gamma emitters and do not glow in the dark. One of the problems with luminous was that it needed frequent re-painting due to failing luminosity. The mechanism for this is the radiation knocking hell out of the fluorescent paint, and nothing to do with half life. (In contrast, the modern Tritium gas luminous devices do have a short half-life.)
Fluorescent instruments which are more common in the 1950s light up very prettily if exposed to UV light, for example from a forged note or security pen lamp. You could try this out, the other giveaway is the lack of gamma radiation (although there are some instruments which have been reworked from luminous to fluorescent and are lightly contaminated with Radium).
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