Light source
From IFWiki
Many classic games and most standard authoring systems include a built-in simulation of the presence or absence of light. The simulation generally takes into account questions such as whether the light source is inside containers and whether the containers are open or transparent.
Many puzzles have centered around the problem of getting a light source into darkness. While it is frequently possible to move into or through dark locations, it is usually treated as impossible to do anything in them. Interacting with objects by feel is rarely implemented.
Infocom games tended to punish movement in darkness by having the player-character be eaten by a mysterious light-fearing carnivore called a grue.