Total losses in output depends on both the LED and the filter. Here is the XM-L2 spectral distribution graph I referenced before along with a visible light spectrum added at the bottom, most lights will be using the 5000K-83000K CCT (aka Cool White) LED's:

Green light is generally around 510-560 nanometers in wavelength, red runs from around 640nm to about 700nm.
Unfortunately most filters will not allow the entire range to pass through -in fact, even at it's peak designed wavelength most decent filters only let through about 85% of the light IIRC. The only saving grace for using a filter on something like the XM-L2 is its frankly beastly luminous flux; of course then you run into the issues of surface brightness and viewing angle which are working against you when trying to collimate that light into a reasonably tight beam for spotting/hunting.
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