UK only, why are street lights in the UK orange ?

Those are "Sodium Vapor" lamps----Sodium has a distinctive "yellowish" color when electrically excited---SO that's why they look "orange", or more properly. a "brownish yellow". It's so bright it almost looks "white", but colors of objects do not look quite right under them. The bright BLUE lights are the "Mercury vapor" lamps--which use an excited MERCURY vapor.

Actually Sodium vapor lights are MORE light polluting---especially as far as observatories go. The Blue/White mercury vapor lights can be filtered out at the telescope---The Sodium ones cant.

Why aren't they pure white?----Only a few vapors or gasses will produce useful light, with good efficiency, when an electric current is passed through them---Mercury and Sodium work the best, so w have to be happy with the colors we get.

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

http://www.thenakedscientists.com/forum/index.php?...

So They don't create as much "Light Pollution." :)

What kind of dumb *** question is that