The filter glass types KG 1, KG 2, KG 3, KG 4 and KG 5 exhibit high transmission in the visible and effective absorption of infrared radiation (heat radiation) in the long wave spectral region and therefore make excellent heat absorption filters (heat protection filters). They are used, for example in slide projectors to protect the heat-sensitive slides from too great a thermal load. These filters are also used as heat protection filters in photocopiers.

An additional application area is the use of these filters in operating room lamps. The essentially colourlessness of the KG filters is the visible spectral range hinders any undesirable colour falsification in operating rooms.