Reply #4: From their patent application.

[drm604]

http://www.freepatentsonline.com/y2007/0200074.html

This invention relates to a means for more efficiently and more safely providing self-luminous lighting devices for use in signs, markers, indicators and the like. The present invention provides self luminosity by means of a plurality of glass or polymer microspheres containing both a light-emitting phosphor and a radioactive gas. The “soft” emission of electrons from the beta emitting gas cannot penetrate the glass or polymer wall of the microspheres, thereby constituting no radiation hazard. A further advantage of the present invention is that the plurality of individual containment microspheres minimizes the escape of radioactive gas in the event of any physical damage to an assembly of such microspheres. A still further advantage of the invention is that the radioactive gas completely surrounds the phosphor particles, thus causing light emission from one hundred percent of the surface of the particles.

This doesn't sound very "green" to me.