The Blacklight

The Blacklight
The blacklight is one of the three main tools. Unlike the hammer and screwdriver which require you to press the button multiple times to unlock them, the blacklight requires you to flick the switch that is unlocked after typing 312213 into the roman numerals.

Behavior
When picked up, the blacklight allows you to gain access to clues that are impossible to find without it and get an achievement called 555-2368.

Gives clues to
Ending 13 (Only in the 3D remake)

Ending 23

Ending 24

Ending 25 (In the 2D remake)

Ending 26

Ending 30

Ending References
Ending 4 (At the floor of the room in the 3D remake)

Ending 5 (At the whiteboard in the 3D remake)

Ending 10 (At the binary buttons)

Ending 16 (On the button)

Ending 25 (In the 3D remake) (At the clock)

Ending 29 (At where the hamsters would be in)

Trivia

 * Using the blacklight, one can find 5 strings of numbers on the right side of the console. Decoding these strings using the A1Z26 cipher (A=1, B=2, C=3, etc.) will return the phrase "DECIPHERING IT WAS COPLETELY MEANINGLESS". Interestingly, the "M" in completely is missing, which could be a reference to something, or even a hint towards a bigger secret. In all likelihood, however, its probably just a developer oversight or something similar.