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Heat Absorbing Filters

SCHOTT KG1, KG2, KG3, & KG5 filter glass

Special Properties

  • Transparent for visible light
  • Absorbs infrared energy
  • Huge heat-blocking bandwidth
  • Almost angle-independent transmissivity
  • Can be thermally tempered for use at higher operating temperatures
  • Largely neutral optical transmission
  • High optical density for infrared radiation
  • More than a hundred different filter materials are kept in stock

Typical Applications

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

Related filters, coatings, and websites

Request for Quotation


Heat absorbing filters made of KG1, KG2, KG3, and KG5 filter glass materials remove heat energy from an optical system in a targeted manner. Such filters are also called heat-absorbing glasses due to their high optical density for infrared wavelengths. KG glass filters allow the absorption of the thermal energy emitted from a light source in lighting systems. While absorbing heat, these glass filters also offer a high, almost color-neutral transmission of visible light.

Heat-absorbing filters in lighting systems get hot during operation. The heat is efficiently dissipated from an optical system by either direct cooling or ventilation of the absorbing filter glass. We recommend the filters' thermal tempering after the polishing and shaping processes whenever heat-absorbing glass must withstand an increased operating temperature range.

KG-Filters do not only work in lighting applications. Many other optical systems profit from the exciting properties of these standard SCHOTT glass filter materials. As the KG-absorption glasses have the advantage of much more broadband blocking of the infrared wavelength range than coated filters (hot mirrors), they represent a better solution whenever you want to block a broad IR spectrum.


Please click on the button below to get a quotation for any SCHOTT KG filter.


Request for Quotation


Online calculator for all SCHOTT filters

Use our online SCHOTT filter calculator to analyze the transmission of all available colored glass filters made of SCHOTT filter material. The calculator allows you to compute individual filter transmission curves and explore the internal and external transmittance of all available glass filters, including surface reflection losses. Of course, you can also analyze KG-heat absorbing filters with our SCHOTT filter app.



KG1, KG2, KG3, KG4, and KG5 Filter
transmission at 200–1100 nm

Enlarge the curve to show details

KG1, KG2, KG3, KG4, and KG5 Filter
transmission at 200–1100 nm

Enlarge the curve to show details


Standard Thicknesses and Dimensions

We fabricate KG absorption filter optics from raw materials in the form of unpolished filter plates. Hence, there are generally no standard thicknesses.

However, a quick delivery (typically 1–2 weeks) is possible for a filter thickness of 1 mm, 2 mm, or 3 mm up to a diameter of 49 mm or, for square parts, up to a dimension of 50 mm × 50 mm. If required, please send us your inquiry, and you will receive our offer immediately.

  • Dimensions max. 165 mm × 165 mm
    (At very high quantities, larger filter sizes are possible)
  • Minimum thickness of 0,5 mm
  • Maximum thickness up to about 4 mm
    (depending on material)


  • Original SCHOTT KG1-KG5 filter glass
    (KG4 has been discontinued)


Thermal Tempering

  • The minimum filter glass thickness for complete thermal tempering is 3 mm


  • Depending on the filter material and thickness of the filters

Surface Quality

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

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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Last update: April 20, 2024