[avandonk]

In my opinion the 'best' light pollution reduction filter is the Hutech LPS-P2.
Below is a picture of spectra I made some time ago.
From the top
Kenko 'H Alpha'
Hutech Nebula filter
LPS filter (brand unknown) but this is typical for most LPR filters.
Hutech LPR filter
Mercury street lamp
High pressure Sodium street lamp
Tungsten globe

As you can see the Hutech LPR has two extra peaks between the light pollution spectral lines. This gives it better colour balance as well as higher useful total transmission of light from stars and nebulae.

All of the pictures I have produced have been from my home in Eltham which is about 20k from Melbourne.

I can expose for ten minutes at an ISO of 400 at 640mm F6.4. At 300mm at F2.8 and ISO 200 I have even exposed for twenty minutes.
With the nebula filter even longer than the LPR filter. The other very good thing about the Hutech filters they are optically very good and If you exchange the Nebula filter for the LPR filter, focus does NOT change. They are optically identical.

Bert