Ron,
The watch dial is photoluminescent paint that "stores" light energy and then glows in the dark until the stored energy is drained (something to do with exciting molecules to a higher energy state that then emit photons (light) until they drop back down to a stable energy state). Radium on the other hand emits radiation (alpha particles I think) that excites a phosphorescent coating causing it to emit light/photons. Radium has a fairly short half-life, radioactively speaking, and eventually due to the combination of reduced radiation and aging of the phosphorescent coating the sight loses its ability to glow. Exposing it to light doesn't restore it. I am afraid my sights, like me, have lost their vigor and no longer shine.
I probably should have included a close up of the back of the rear sight in my first post so that it would have shown that there are also radium inserts in it. In the dark it presents a sort of "three dot" night sight picture (actually a dash-dot-dash picture
)
