Incandescent lamp

1. How it Works

Incandescent bulbs work by sending electric current through a resistive material. Typically materials will glow before reaching a melting point. Most materials will glow a dull red color when they reach around 525 Celsius. Most materials will catch fire or melt and can not make a good filament.

Filaments are made from materials that have a high melting point. Tungsten can reach up to 3422 C before it melts. This is a higher temperature than any lamp will reach (except the carbon arc lamp which gets to 3500 C). Other materials have made good filaments or parts of filaments including tantalum, molybdenum, and carbon.

Why does the material emit light when you pass electrical current through it?

When you pass current through a filament material, the resistance creates heat. Atoms in the material absorb energy. Electrons around the atoms are excited and temporarily reach an orbital which is further from the nucleus. When the electron orbit collapses to a lower orbital it ejects the extra energy in the form of a photon.

Incandescence is thermal radiation. Heat is constantly emitted from objects around us, we just can't see it. When heat gets intense enough it reaches wavelengths that we can see. It starts with red and goes up the spectrum. The wavelength/color of the light is a matter of how much energy is being released and what kind of atom is doing the release. In an incandescent bulb most of the heat energy (90%) is emitted in the infrared spectrum which is just below visible light. This is also what makes the lamp inefficient. We don't use that part of the spectrum for the lamp's purpose, we only need the visible spectrum. This is a basic explanation.