The Spotlight is a gimmick/obstacle that appears in the Sonic the Hedgehog series. It is a light tower that can be used for various actions.
Shadow the Hedgehog
The Spotlights made their first appearance in Shadow the Hedgehog, where they only appear in Digital Circuit. When stepping into their light column, Shadow is transported through said light column to another area, which is often a necessity. At times, Shadow passes through the source of the Spotlight, causing it to shatter. Sometimes, the player cannot reach the Spotlight's light column alone, so they have to skip across enemies with the Homing Attack to reach it.
Sonic the Hedgehog (2006)
In Sonic the Hedgehog (2006), the Spotlights consist of large metallic quadpods with supports and a large searchlight on the top that shines white light. They are only found in White Acropolis and End of the World.
In gameplay, the Spotlights are warning system to the player's presence. If the playable character enters the Spotlight's light column, it will track the playable character's movements and cause enemies to appear around them. However, the Spotlight can be disabled by destroying its searchlight.
In Shadow's version of White Acropolis, the player has to destroy five Spotlights with the Buggy to complete this Action Stage for the normal version and all of them in the Very Hard Mode version. If the player destroys one of the Spotlights' glasses and leaves the area, the glass will be restored upon return. In the Very Hard Mode version of the same stage, breaking a Spotlight's glass can open Cases and make Keys appear. In the battle with Egg-Cerberus, the spotlights also help the boss locate Shadow. In End of the World, they are most likely controlled by Solaris as they help his minions locate the player.