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Discussion in 'Exposure Discussion' started by Mike Kennedy, Jul 15, 2010.
Is there a filter I can use to eliminate the nasty yellow cast?
From my days as a Facilities Engineer (1970's), I recall that sodium vapor lights have a very limited spectrum. The low pressure ones especially so. There is just no blue end, so filtering out the red-yellow would leave practically nothing.
They're not like flourscent which has a discontinous spectrum but does have red and blue parts.
The "no blue" applies to the high pressure variant (though it should read "almost no").
The rest of the spectrum they produce is patchy, with gaps, but with some of all colours represented. Maybe (never tried it myself) a tungsten balanced film, without filter, will produce better results. A filter used on daylight balanced film would do not much good,
Low pressure sodium has just the double D line.
There's only one thing you could do using a filter, and that is remove the little there is and be left with nothing at all.
Both sodium and mercury vapor lamps have what is called a discontinuous spectrum. There are no filters which can produce satisfactory results. If you wish to get good images under such lighting conditions use B/W.
I think you should try tungsten film. I've seen examples of urban night photography that are very good, though can't say for sure if they're sodium vapor per se.
Also, here are spectra.... http://en.wikipedia.org/wiki/Sodium-vapor_lamp
Update.... aahhh, actually you're probably screwed... http://www.flickr.com/photos/grooveb/383751061/
Sodium street lights used to use cadmium as a lower temperature starter (that's why they were a dirty orange colour when they started), then the sodium warmed up enough. So you had cadmium and sodium lines.
Do a google search for sodium spectrum to see what the light looks like.
The Wiki linked to above is pretty good.
Unusual for Wikis, but hey!