It is a kind of filter that has a very high transmittance, and the light of other band has a very low reverse (pass through). For example, long wave, double pass band, three, RGB Filter, etc..
Main technical index:
Narrow band: half width is much smaller than the cut-off band width, known as the narrow band pass filter; such as XBOX, Leap Motion narrowband sensing equipment such as body.
Spectral characteristics (for reference)：