That's called a 'Light Emitting EPROM' and
it's an expensive and
short-lived alternative to an LED.
Is this related to things like the SER (Smoke Emiting Resistor -- one
where the power rating is massivle exceeded), SEC (Sound Emitinf Capacitor
-- an electrolytic wired backwards), the Friode (a diode that's
open-circuit both ways), etc?
-tony