LPR filters

[wulfrunian]

Is there any way of finding out whether your particular light pollution matches an LPR filter? Or is it just a case of trying them out to see?

[michael.h.f.wilkinson]

If you can get hold of one beforehand (borrow one from a fellow astronomer) and look through it at the offending lights, you can see whether these lights all but vanish. Alternatively, find out what lights are used predominantly in your neighbourhood. If they are the (orange/yellow) low-pressure sodium types, many LPR filters will do a great job. Slightly greenish-white mercury-vapour lights have both strong line emission (which is suppressed well) and a continuum (which is not suppressed well). High-pressure sodium lights are even worse in this respect. You will need stronger filters to see deep sky in that case.

[wulfrunian]

High-pressure sodium lights are even worse in this respect. You will need stronger filters to see deep sky in that case.

I've just looked on Wolverhampton council's website, and their street lighting policy says that high pressure sodium is their lighting of choice

[michael.h.f.wilkinson]

LPR filters still help. There is still a very strong line emission component in high-pressure sodium lights. Besides, LPR filters also block out part of the continuum, allowing mainly the hydrogen and oxygen emission lines of the DSOs to pass.