Cyalume Chemlights/Chemsticks

[FelixEstrella]

I had a bunch of green ones that didn't "go off", but they'd been sitting around for 15 years.

[The Wizard]

well ill chime in
we use chemlights for everything over here marking turns, low wires, IEDs, pot holes, trailer lights, downed vehicles, hell we even hacky-sacked with them at night and the only ones i have ever had that didnt work were already cracked. i know that if you leave them in the sun all day they arent as bright as if they werent in direct sunlight but they still work.

[Aegis]

I had a bunch of green ones that didn't "go off", but they'd been sitting around for 15 years.

It's possible that the chemicals inside leaked around the isolating capsule, in small enough quantities that it would never be noticed glowing on its own, but just enough for the chemicals to deplete themselves over the course of the years.