Radioluminescent Chain Pulls (ca. 1930s)
These small glass vials, sometimes referred to as "acorns," contain a radioluminescent material so that they can be seen in the dark. They were attached to a bead chain that served as the pull for a light switch—an electric light is no help unless you can find the switch. The radioluminescent material is a mixture of radium-226 and zinc sulfide.