"Maintenance-Free Emergency EXIT Sign Never Needs Electricity," proclaims the catalog. One such sign sells for $13.35 and lasts forever. Another sells for $344 and expires in 10 years. Which is the better buy?

OK, it's a trick question. The cheap exit is printed on vinyl in glow-in-the-dark letters and is designed to be tacked to the wall; when the lights go out, it starts fading. The costly exit is spelled out in glowing tritium gas and enclosed in a frame; when the lights go out, its letters stay bright.

Sparked by recent office disasters, upgrades of emergency signs are "the latest safety bandwagon," reports D&G Sign & Label, a Northford, Conn., manufacturer and distributor. Thus, there's increasing demand for signs illuminated by tritium -- an isotope that, when combined with phosphor, releases light but requires no outside energy source. Tritium signs meet Occupational Safety and Health Administration and other safety standards. -- Researched by Phaedra Hise

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