These filters can be used in astronomy and astrography to block the parasitic radiation of urban and industrial lighting, 

determining the increase of contrast for observations in:

H-alpha (656.3nm), N II (658.3nm) and SII (673.1nm) for the visible spectrum

and all wavelengths of interest in the IR: Ca II (854.2nm); S III (906.9 nm) etc.

These filters are also useful in any didactic or laboratory experiments where it is necessary to select the red + IR spectrum (l > 600nm - see the graph in photo gallery)