WTF? Phosphorescent power supply

I’m not sure what to make of this: last evening I played around with a new hardware device (a TP-Link TL-MR3020 router, but that’s not the point). I was leaving the room and just as I turned off the lights I noticed a green spot on my desk. The USB power supply of the device emitted a green phosphorescent glow (Wikipedia).

Phosphorescent power supply (under normal lighting)

Phosphorescent power supply (ISO 100; 30 seconds exposure)

I’m not sure why the manufacturer used a phosphorescent material for the case of the power supply, but the effect is quite impressive (creepy) and lasts for some minutes. By the way, it’s a Huntkey Switching Power Adapter model HKA00605010-3B.