On and Off Barrel
From the Super Mario Wiki
As suggested by their name, On and Off Barrels act similar to light switches. They are either found on the ground or in mid-air. By default, every On and Off Barrel has the white text 'OFF' painted on them. If Donkey Kong and Diddy Kong touch an On and Off Barrel, all of them change to 'ON'. This causes the level to illuminate for a few seconds, allowing the Kongs to see the path and the enemies ahead. On and Off Barrels are similar to the Stop and Go Barrels from Stop & Go Station.
In the Game Boy Color remake, Loopy Lights is not as dark while the On and Off Barrels are turned off. In the Game Boy Advance remake, the level has a maroon tint while they are off, making it even less dark.
In Donkey Kong Land 2 during the level Glimmer's Galleon, there is a type of barrel similar to the On and Off Barrels. They have a small light bulb icon displayed on them, and when Diddy and Dixie touch one of these barrels, they temporarily brighten up the level.