Copper bulbs are found naturally in trial chambers and can be crafted from three copper blocks, one blaze rod, and one lightning rod arranged in a specific pattern. They function as a light source with an unusual toggle mechanic: a redstone pulse switches them between lit and unlit states rather than keeping them powered only while the signal is present, so a single click from a button or comparator changes state permanently.

Light level depends on oxidation stage. A fresh or waxed copper bulb emits level 15; exposed emits level 12; weathered emits level 8; oxidized emits level 4. Because oxidation in open air gradually reduces brightness over time, builders often apply wax with a honeycomb to lock the bulb at the desired brightness stage.

Copper bulbs are the only light source whose brightness declines without player intervention, making them both a functional lamp and a natural long-term timer. When powered by redstone they emit one level lower than their oxidation state and appear slightly dimmer, useful as a visual indicator of circuit state in compact builds.