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ELI5 Yahaaa

A wire too hot to stay dark

How Does Electricity Become Light?

A filament bulb makes light by heating a thin wire until it glows; an LED skips the heat.

A glowing bulb A coiled wire, white-hot
The wire fights the current, gets hot, and glows.

  1. Step 1 of 5

    One thin section does all the work.

    Thick supply wire — coolcarries chargeinThin filament — whitehotwhere theresistance sitsThick supply wire — coolcarries chargeback out

    The wires feeding a bulb are thick and stay cool. Only the filament is thin, and that is where the current has to squeeze through.

  2. Step 2 of 5

    Resistance turns electricity into heat.

    Electrons bumpthrough the metal The wire heats up

    Electrons bump their way through the cramped metal, and every collision leaves energy behind. That energy has nowhere to go except into heat.

  3. Step 3 of 5

    Anything hot enough starts to glow.

    Warm — 200°Cinvisible heatonlyDull red — 800°Cyou can just seeitWhite — 2,500°Cbright enough toread by

    Heat and light are the same family. Warm metal radiates invisibly, dull red metal is just visible, and metal near 2,500°C pours out white light.

  4. Step 4 of 5

    The glass is there to keep oxygen out.

    Glass envelopeArgon or vacuum insideNo oxygen, so noburningCoiled tungstenfilament

    A wire that hot would burn away in seconds in open air. The bulb is filled with argon or emptied entirely, so the filament can glow without burning.

  5. Step 5 of 5

    An LED skips the heat entirely.

    Filament bulb Light as a side effectof heatLED Light made directly,barely warm

    Instead of getting hot, an LED nudges electrons across a gap in a crystal, and each one gives up its energy directly as a packet of light.

    An old filament bulb turned only about 5% of its electricity into light and the rest into heat. A modern LED manages around 40%.

The short version

A filament bulb makes light by heating a thin wire until it glows, which wastes most of the energy; an LED makes light directly instead.

Try it yourself

Turn a dimmer switch up slowly. The bulb goes dull red, then orange, then white — one wire at rising temperatures.

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