Light in the darkness
I'm not sure whether this particular style is still available new; I would guess that it's not as popular as when it was first introduced. I rarely see anyone actually using one for prayer. For sheer rock-bottom cheapness, it's been superseded by another type, where the beads are molded directly onto a connecting string:
Collectors, however, still like the "classic" chain-structured form like the one I bought, and rosaries like that one sell very well on eBay for close to the same price as new rosaries.
The commercial use of chemicals that absorb energy in daylight and glow dimly in the dark afterwards dates back at least to the 1930s. Zinc sulfide with minute amounts of copper added was one of the first such compounds discovered, and since it's quite cheap and easy to make, it begins to show up in specialized markets as early as 1947. Unlike the glowing hands of some wristwatches (which require no "recharging") no radioactive materials are involved -- it's a purely chemical process, and even relatively nontoxic -- the FDA allows small amounts to be used for Halloween makeup.
Glow-in-the-dark plastic hit the consumer market in the late 1950s and early 1960s and became an instantly popular gimmick for all kinds of uses, ranging from practical (light switches) to ridiculous (fright wigs). Zinc sulfide produces a rather dim greenish glow -- you really have to be in almost complete darkness to see it. It also doesn't last very long, glowing for anywhere between fifteen minutes and an hour or two. Other "phosphors" (as the glowing substances are called) discovered more recently, such as strontium aluminate and various cadmium compounds, will glow for several hours. Newer compounds may also be brighter and glow in different colors.
The reason to own a glow-in-the-dark rosary somewhat escapes me. I'm sure it is rationalized as "you can find it in a dark bedroom," and perhaps others do wake up from nightmares at 2:00AM and reach for the rosary more often than I do.
But I suspect its real appeal is the pleasure (usually an innocent one) of having a rosary in a new and fashionable material. A somewhat childish pleasure, I admit, but did not Jesus say we must become like little children?