Light Detector

This hand-sized metal plate is covered with a thin layer of light-sensitive transparent paste. If exposed to light, the paste darkens and becomes opaque, depending on the amount of light. Bright light causes it to fully darken in 1 round, normal light in 3 rounds, dim light in 10 rounds. It is mainly used by creatures with darkvision to determine if creatures have recently passed through an area carrying light. The plate is sold wrapped in a thick black cloth to prevent accidental light exposure from ruining the plate.