I have a question I could not find an answer for on the 'Net.
Radium (used as ingredient in Luminous paint for dials in the old days) is Radioactive all the time (very long half live).
Why do you need to "charge" it under a lamp or sun to get the max. and most long lasting lume?
Should it not be luminous at the same strength at all times, not depending on the charging?