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Heat Absorbing Filters KG1, KG2, KG3, KG4, & KG5


Special Properties

  • Very 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

Request for Quotation


The SCHOTT glass filters KG1 to KG5 allow the absorption of thermal energy. They are called heat absorbing filters due to their high optical density in the infrared wavelength range. The glass filters are often used in lighting systems to absorb the thermal energy emitted from a light source. At the same time the glass filters offer a high relatively color-neutral visible light transmittance. Absorbing filters in lighting systems heat up during operation. Therefore the heat can be easily be removed from a system by direct cooling or ventilation of the absorbing KG glass. If heat-absorbing filters must withstand increased operating temperatures it is recommended to thermally harden the filter glass after the polishing and shaping processes.

But KG-Filters are not only used in lighting applications. There are many other optical applications that profit from the special properties of these standard SCHOTT-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 an ideal solution whenever a wide IR-spectrum should be blocked.

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


How can I order the heat absorbing filters?

All polished optical glass-filter optics at dimensions at up to 50 mm x 50 mm and below as well as diameter 49 mm and below at thicknesses of 1,00 mm, 2,00 mm or 3,00 mm typically are shipping within one working week. To get a quotation for a 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. The calculator is online at your free disposal. You can compute individual filter transmission curves and choose to see 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 filter app.



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

View internal transmission curve at 1000-4600 nm



  • Original SCHOTT KG1-KG5 filter glass material


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 filter products are available on request.


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