The Baader UHC-L filter is an all-round anti-light pollution filter that also blocks the emissions from LED lamps in the blue part of the spectrum.
The two pass bands transmit all light emitted by the known emission nebulae (the H-alpha and H-beta lines of fluorescent hydrogen as well as the OIII oxygen line).
In addition to stray light from LED lamps and classic street lamps, these filters also block the light from bluish car headlights. Even the atmosphere’s natural night sky glow (airglow/skyglow) is largely blocked.
The transmission curve shows how much incident light of a given wavelength can pass through the filter.
The UHC filter transmits the colours emitted by the universe’s emission nebulae, but blocks other wavelengths that do not occur with these astronomical objects. This greatly increases image contrast.