AstroSG Please enlighten me. Thanks.
White light spectrum wavelength is from approx 380 nm to 750 nm. That's about 370 nm worth.
If you are using a dual band filter where each band is 5 nm wide, that filter is letting through 10 nm worth of the white light, or 2.7%, or a factor of 37.
In practice, it will depend on the background light pollution spectrum. Just measure it yourself after you buy the filter. For the above, just start at 40 and then measure, measure, measure.
Chen
