The Thieves Light takes the form of a lense, which can be attached to a bullseye lantern, or else hung from a string as an amulet. Any light passing through the lense is invisible to anyone who isn't either holding the lantern, holding the lense itself (if it was targeted by a light spell) or wearing the lense. There is one notable exception. Of 2 people are touching the lantern the lense is attached too, both see the light. If the light is centered on the lense itself, anyone holding the person wearing or holding it can also see the light. 

There is 1 notable weakness. Anyone currently in an effect that allows them to ignore invisibility can always see the light, giving away the user's position.

Notes: Utility, Jewelry