My girlfriend got herself a pair and taped them to corners of her desk. She doesn't want to turn on the light when she gets up at night but she also doesn't want to bump into the desk. Tritium vials fit that use case well.

Could we have gone with dimmable lights or something homebrewed with low-power LEDs? Sure, but tritium vials are affordable and don't need a power supply, a remote, or much in the way of setup; they'll just keep doing their thing for about a decade before you have to even think about their light output.

They're a solid choice if you have the specific use case of wanting something to be easily located in (near-)complete darkness but you don't want to use electricity for some reason.