What is this light-emitting component?
Looks like and EL panel.  EL= ElectroLuminescent.
They glow when they have a sufficient electric potential across them.  They do not consume much power, as they act like a capacitor.  Your's may have a built in diode, or they are just relying on the small capacitance to not pass much current.
EL Panel on Adafruit.com