The Optolong L-Pro (L-Professional) is a multi-band filter designed for visual observation and photography, improving the visibility of various Deep Sky objects by selectively reducing the wavelength transmission corresponding to artificial emission. Thus, it cuts out the mercury vapor emission line (mercury lamps), the light of sodium lamps, both low and high pressure sodium vapors, and also the natural emission of atmospheric oxygen ( skyglow ). At the same time, the lines O-III, H-beta, N-II, H-alpha and S-II pass through with high efficiency.
The difference between the L-Pro and the UHC and CLS is in the better color balance in the case of the L-Pro, which on the one hand gives a high transmission in the lines of interest to us, and on the other hand, a natural color balance.
More information about Optolong filters and the manufacturer on the product page (active link 06.2020): optolong.com/cms/document/detail/id/15.html