The Schott heat absorber filter glass KG3 permeable to UV radiation and blocked infrared radiation down 900nm due to absorption. I offer this filters with a additional dielectric UV/IRcut interference coating block until IR 1200nm on the first surface.
The 2nd surface is AR coated to reduce reflections.
Filter band pass is 400nm...680nm wavelength.
These filters are used in conjunction with an ERF filter in front of H-alpha systems or Herschel wedge to eye safe observe the sun.

The 20mm size (no cell) is recommend as replacement for the blue-green filter in the Lunt B600, B1200 and B1800 blocking filter modules if you want a brighter H-alpha image in the double-stack modus with a 2end etalon filter.