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Heat Absorbing Filters

SCHOTT KG1, KG2, KG3, KG4, & KG5 filter glass

Special Properties

  • Broadband heat blocking range
  • Absorbs IR-energy
  • Transparent for visible light
  • Almost angle-independent transmissivity
  • Can be thermally hardened for higher operating temperatures
  • Largely color neutral
  • High optical density for infrared radiation

Typical Applications

  • Heat absorbing glass filters in lighting systems
  • Sensor technology
  • Standard IR-absorbers
  • Heat protection filters
  • Protective filter for projector optics

Related filters, coatings, and information

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Heat absorbing filters made of KG1, KG2, KG3, KG4, and KG5 filter glass materials allow to remove heat energy from an optical system in a targeted manner. Due to their high optical density in the infrared wavelength range, such filters are referred to as heat-absorbing glass. This kind of glass filters is often used in lighting systems to absorb the thermal energy emitted from a light source. While absorbing heat, the glass filters also offer a high, relatively color-neutral transmission of visible light.

Heat-absorbing filters in lighting systems warm up during operation. Therefore, the heat can efficiently be dissipated from an optical system by direct cooling or ventilation of the absorbing filter glass. Whenever heat-absorbing filters must withstand increased operating temperatures, it is recommended to thermally harden the filters after the polishing and shaping processes.

KG-Filters are not only used for lighting applications. Many other optical systems profit from the unique properties of these standard SCHOTT glass filter materials. As the KG-absorption glasses have the advantage of a much more broadband blocking of the infrared wavelength range compared to coated filters (Hot Mirrors) they represent a better solution whenever a wide IR-spectrum should be blocked.

Our high-quality KG glass filters are fabricated from original SCHOTT filter glass which exists as unpolished raw material squares or rolled sheet materials. The heat absorbing filter optics are ground, polished, and shaped to customer's specifications. Please use our inquiry form to request a quotation for your custom-made heat-absorbing filters. For further details and specifications, please email us.


How can I order the heat absorbing filters?

All polished optical glass filters at dimensions up to 50 mm x 50 mm or up to a diameter of 49 mm and at filter thicknesses of 1,00 mm, 2,00 mm or 3,00 mm typically ship within one working week. Other dimensions up to 160 mm x 160 mm are of course possible too.

To get a quotation for an KG-heat absorbing filter, please click the button below:


Request for Quotation



NEW! Our SCHOTT-Filter Online Calculator

Use our online SCHOTT-filter calculator for the analysis of the transmission of all available color glass filters made of SCHOTT filter material. You can use our online calculator free of charge. The calculator allows you to compute individual filter transmission curves and to choose to display the internal transmittance or the external transmittance of the glass filters including surface reflection losses. All KG-heat absorbing filters can be analyzed with our SCHOTT filter app.



View transmission curve of KG1, KG2, KG3, KG4, and KG5
IR-absorbing glass filters at 200-1100 nm

View internal filter transmission curve at 1000-4600 nm



  • Original SCHOTT KG1-KG5 filter glass


Thermal Tempering

  • minimum filter glass thickness for full thermal tempering: 3 mm


  • Depending on filter material and thickness of the filters
  • Other on request

Surface Quality

  • typ. 80-50 scratch & dig (MIL-0-13830A)
  • Other on request

Max. Dimension

  • 164 mm x 164 mm (square filters)
  • ø 150 mm (diameter filters)
  • larger filter sizes possible at large quantities

Further detailed information about all KG-glass filters is available on request.


All given details and specifications are mean reference values and are not guaranteed. Also, please consider our "Notes on technical specifications".

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