That depends on the source(s) of light pollution, but the best way to know for your location would be taking a few alternate exposures with a Lum filter and a light pollution filter and see which one has the highest SNR. If light pollution is heavy though, then I would drop the idea of using LRGB filters altogether and do narrowband only (that's what I used to do when I lived in Sydney and Brisbane).
I used to use LP filters (tried them ALL, including the VERY expensive one from Cyclops). I got FAR better results by using no filter and letting PixInsight deal with it instead. The results are QUITE noticeable. I still do OSC, and also now mono LRGB-Ha.
MY LP issue has been stated a buzzillion times - it is horrendous.
I am under the impression that the LP Filter would reduce the LP much more than the 'L' filter,,,
Have a read through my recent thread : Does LRGB Imaging cut through Light Pollution http://www.iceinspace.com.au/forum/s...d.php?t=169584
Hope helps ?