Heat Absorbing Filters
SCHOTT KG1, KG2, KG3, & KG5
Special Properties
- Transparent for visible light
- Broadband thermal absorption
- Wide IR-blocking bandwidth
- Almost angle-independent transmissivity
- Can be thermally tempered for higher operating temperatures
- Largely neutral optical transmission
- High optical density for IR radiation
Typical Applications
- Heat absorbing glass filters in lighting systems
- Sensor technology
- Standard IR absorbers
- Heat protection filters for lenses and lens systems
- IR-laser blocking applications
- Protective filter optics for projectors
Related filters, coatings, and websites
- SCHOTT Filters (> 100 different stock filter materials)
- SIR-Series (dielectric heat-reflecting hot mirrors)
- SIR-IR Series (heat reflection filters (extended IR-blocking range)
- SCHOTT filter calculator (filter curve generation)
Heat-absorbing filters made of KG1, KG2, KG3, and KG5 specifically dissipate heat energy from an optical system. 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 either by direct cooling or by ventilating the absorbent 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 IR 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.
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 material. The calculator allows you to compute individual transmission curves and explore internal and external transmittance, including reflection losses. You can also compare filter types in one curve and simulate cemented filter combinations. Of course, you can also display and analyse all KG heat absorbing filter curves.
Where is the KG4 filter?
Production of the KG4 filter material was discontinued many years ago. However, we may still have some remaining stock on hand. Please send us your inquiry if needed.
Specifications
KG1, KG2, KG3, and KG5 filters
Spectral transmission at 200–1100 nm
Display transmission curve in the filter calculator
KG1, KG2, KG3, and KG5 filters
internal transmission at 200–4200 nm
Display internal transmission in the filter calculator
Note: Spectral transmission includes the naturally occurring reflection losses in air and therefore provides a realistic representation. Internal transmission does not account for these reflection losses. In our filter calculator, you can select the type of transmittance you want to view and freely adjust the wavelength range..
Standard Thicknesses and Dimensions
We fabricate KG absorption filter optics from raw materials we keep in stock 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 up to 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 stock material)
Materials
- Original SCHOTT KG1-KG5 filter glass
(KG4 has been discontinued)
Coatings
Thermal Tempering
- The minimum filter glass thickness for complete thermal tempering is 3 mm
Flatness
- Depending on the filter material and thickness of the filters
Surface Quality
- typ. 80-50 scratch & dig (MIL-0-13830A)
- Other surface qualities on request
Further detailed information about all KG glass filters is available on request.
All data and specifications given are average guide values and are not guaranteed. Moreover, please consider the “Notes on Specifications”.© 1994 – 2026 Präzisions Glas & Optik GmbH
Last update: March 26, 2026