sodium vapor light

[mozhigopi]

Why sodium vapor light glowing yellowish?

Edited July 19, 2008 by swansont
turned volume down

[Klaynos]

Please don't edit your font size, it's just a bit annoying.

 

It's to do with electron energy levels, the highest emission from the energy level transitions in sodium is for photons with an energy that are yellow.

[iNow]

Hello mozhigopi,

 

The simple answer is that they are yellowish in color because that is the wavelength of light that they emit (about 589 nm wavelength).

 

As you may know, the different colors of light have different wavelengths associated with them. In the visible range of the electromagnetic spectrum, the wavelengths break down roughly per the image below, where reddish colors have a longer wavelength than blueish and purplish colors:

 

 

 

 

 

Sodium, when studied using spectroscopy, turns a bright yellow color.

 

 

 

There is also a good article on wiki that describes this in greater detail. Please review it and let us know if you have other questions. I may not know all of the answers, but there are a good group of members here who, when working together on an explanation, can help us all to fill gaps in our knowledge and understanding.

 

http://en.wikipedia.org/wiki/Sodium_vapor_light

 

 

Enjoy.

[YT2095]

pure electricity alone will actually give a Violet to UV light 1`st, Then with the addition of heat you`ll get yellow.

 

</interesting factoid>

[John Cuthber]

What do you mean by "pure electricity alone will actually give a Violet to UV light 1`st, Then with the addition of heat you`ll get yellow."

[YT2095]

probably easier if I show You.

here you can see the plasma conduit taken (Very Carefully) from a sodium vapor lamp, and it has a high frequency high voltage current passing through it, and you can clearly see the UV light coming from it.

this is can also be seen to a less exagerated degree daily when a sodium street lamp 1`st fires up.

 

 

this of course is quite useless as a light source, so Heat is needed to give the Yellow light, as seen here:

in a Street lamp, this heat is achieved by having 2 electrodes close together on one side of the conduit and a high current pass through them to make the gas hot, in my instance I`m using a simple bunsen burner instead. the very old ones actually had a heater wire close to the tube.

 

I hope that clears it up nicely for you

Edited July 20, 2008 by YT2095

[John Cuthber]

"you can clearly see the UV light coming from it."

A clever trick.

That light is from the innert gas filling, rather thasn sodium. Until the Na gets warm there's no Na vapour in the tube to emit yellow light.

[YT2095]

and indeed typical of sodium street lamps (where I got this tube from), I suppose it is quite clever how they arrived at this design and mixture, although I`d be somewhat hesitant to call it a "Trick".

 

the sort I`v shown above is the Low Pressure type of sodium light, and although not quite clear in the picture is a Very distinct electrical arc inside it, you can also see condensed particles inside on the tube wall (probably sodium amalgam).

[mozhigopi]

But, I saw some times, when I switch on the sodium lamp its glow in pink color in beginning. Why?

[John Cuthber]

"you can clearly see the UV light coming from it."

Last time I checked UV was invisible, that makes it a clever trick.

Many street lamps contain neon in order to get the lamp started. If they just had Na in then, when they were cold, there would be no vapour to cary the current. Once the current through the neon warms up the sodium it carries most of the current.

[YT2095]

a clever trick because the cam is sensitive to UV?

yeah, they can do all sorts of wonderful things with CCD technology nowadays, I think you`re getting off topic though.

[insane_alien]

Last time I checked UV was invisible, that makes it a clever trick.

 

ah so microscopes, telescopes, TV/radio receivers, internet modems, electrical power distribution networks, MRI scanners etc. etc. are all clever tricks too then? they all rely on stuff that we cannot interpret with our senses and often deal with invisible stuff.

 

we can detect them through machines, no trickery involved. if he was to pull a rabbit out of the light then there might be some trickery afoot but alas i see no rabbit in the photos. quit with the over obsessive nitpicking, even nasa will say that when they are showing you pictures from a UV sensor.

[John Cuthber]

OK, I apologise for going off topic. BTW since the OP is about yellow light from sodium could someone let me know how on-topic UV light from some other element (Ar, Hg, whatever because it's not clear why the Na would be amalgamated unless they happen to be using Hg as a filler gas) is?

 

The point I made is that the blue colour (UV in the original) isn't due to sodium. As soon as you warm the tube and get some sodium vapour, the light turns yellow. Hardly nitpicking to say that non- Na lamps don't glow yellow.

Also, since the camera renders UV as blue it's not clear that I'm seing UV- I couldn't tell if I was seeing blue or UV.