While in use, the blacklight illuminates a cone-shaped area in front of the player with purple UV light. Unlike other light sources, the UV light from the blacklight does not anger Squiddles. Using a blacklight will slowly drain its charge until empty, at which point the blacklight will become inoperable unless recharged with batteries. Using a battery will give the blacklight an additional 50% charge, and allow it to be used for 36 more seconds.
The blacklight has a shorter battery life and weaker light output compared to other light sources, making it difficult for regular use.
While the light from the blacklight does not anger Squiddles, other player interactions, such as standing too close, will still cause them to attack.
Unlike many items, the blacklight gets held at the player's hip level unless it is on, meaning players who have their blacklight off will not generally see the blacklight's model in first-person.
Gallery
The player holding a blacklight in a dark room
The player safely shining a blacklight at a Squiddle
Research. If the player has the "We Die in the Dark" achievement, the blacklight can be purchased from the Pre-Round Shop for 100 
Kroner.
The player holding a blacklight in a dark room
The player safely shining a blacklight at a Squiddle
