Light bulb operation

Most devices we call light bulbs use electrical energy to excite atoms to produce photons. Photons are light energy. A typical incandescent light bulb is constructed of a bulbous, thin-walled, glass envelope. Sealed inside the glass is an inert gas such as argon or nitrogen. Also inside the glass is an electrical circuit. It consists of a resistor called a filament. The filament allows current flow through it by means of a pair of contact terminals on the socket of the bulb. The filament is typically made out of tungsten. Current flow heats the tungsten filament up to a white-hot temperature. Like any heated metal, the tungsten becomes white hot, something in the region of 4,500°F (2,500°C). A metal heated to these kinds of temperatures emits both heat and visible light in a reaction known as incandescence. Visible light energy is radiated as photons.

Incandescent light bulbs use a thermal radiation principle. Thermal radiation light bulbs are not especially efficient because much of the electrical energy consumed is radiated as heat as well as photons. A typical light bulb lasts until the tungsten in the filament vaporizes, creating a high-resistance spot, following which the bulb burns out.

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