Why are streetlights orange?

03 April 2012



Why are streetlights orange?


The reason that most streetlights are orange is because they contain the chemical sodium.

Some electricity is passed into the lightbulb and this gives energy to the sodium. Sodium, when it gets excited by the energy, gives out a lot of orange light, making it a very cheap and efficient way to illuminate a very large area.

But to produce white light is very complicated. To make white light you have to mix lots of different colours of light together and it's the mixture that looks white.

The way in which lamp designers make this happen is to use a mixture of different chemicals. When each of those chemicals gets excited they then produce different colours of light which you then see mixed together so it appears to be white.

Because it's more complicated and involves more chemicals, it's more difficult to do and it's more expensive and because orange light does a good enough job, most of the time we use orange sodium lights rather than white ones.


I’m from South Africa but I now live in the USA. I notice every time I fly into Cape Town at night, I can see orange street lights everywhere. It’s very interesting. It must be because it’s cheaper like you said.

I am wondering who discovered and or invented this, and am particularly insterested if this person is from New Hmapshire. Thank you.

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