Bulbs glow because a thin filament resists the current and heats until it shines.

The longer version

A thin filament inside a bulb resists the flow of current, and that resistance turns electrical energy into heat. The metal reaches such a high temperature that it glows, emitting visible light along with a great deal of infrared radiation. Most of the energy leaves as heat rather than light.

Ordinary metal would burn away instantly in air, so the filament sits in a sealed space with little or no oxygen. Tungsten is used because it melts only at a very high temperature and can glow brightly for a long time. Eventually it thins and breaks, ending the bulb's life.

Where this entry sits

Everyday physics and chemistry hide small wonders in plain sight, from kitchen reactions to the light in the sky. These short facts explain matter, energy, electricity, magnets, sound, and the simple units we use to measure the world. The full list sits on the Science and Physics page, where every entry is listed in order.