A so called hot mirror is a dichroic optical heat filter that is mainly used to remove undesired infrared energy from a light beam. Such mirrors reflects infrared wavelengths while it is transparent in the visible spectrum, which is the opposite function principle of a cold mirror. Since a hot mirror reflects and filters IR-light, it can be called a filter or a mirror.
Our SIR heat filters offer a decisive advantage over ordinary hot mirror coatings and heat absorbing filters: The transmittance of visible light is higher and more neutral in color, while the thermal radiation up to 1100 nm (near infrared light) is reflected significantly more efficiently. Because of its 100 % dielectric optical coating construction and the temperature-resistant quality BOROFLOAT® substrate, the SIR mirrors can withstand a high thermal load. The optical filter can therefore be used at operating temperatures of up to 400 °C, which enables the use in lighting systems. Furthermore, our heat reflecting hot mirrors don't warm up as strong as heat absorbing filters do, because the warm infrared radiation is deflected instead of being absorbed. But there are also purely optical applications where our SIR hot mirro doesn't have to remove thermal energy. For example our SIR filters are often used as detector trimmers in front of digital camera chips to prevent the optical image sensor from saturation, caused by the near infrared light for which many optical camera sensors are very sensitive.
The non-metallic filter coating design makes the SIR hot mirror resistant to humidity and in terms of many other environmental conditions. The SIR filter coting is designed for maximum optical transmittance of visible light and at the same time for maximum reflectivity in the NIR range at an angle of incidence of 0°. If however a shifting of the cut-off is acceptable, even our standard SIR mirrors can be used at incidence angles of 45°, while still transmitting most of the VIS light spectrum. The reflected IR-image maintains a good imaging quality when the SIR is used as a 45° mirror. Hence, the SIR hot mirrors can often be used for optical eye-tracking systems without modification. If you want to utilize our SIR filters at other optical incidence angles than 0°, please contact us by email or simply use our support form to get further information and typical transmittance curves of our hot mirror at 45° incidence.
All of our heat reflecting mirror coatings can be modified in regards to optical transmittance and reflection wavelength ranges, as well as to the cut-on and cut-off filter wavelength and angles of incidences. Please use our inquiry form for custom optics, to conveniently inquire your custom designed hot mirror or just contact us for help, further information and details.
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All given details and specifications are mean reference values and are not guaranteed. In addition, please consider our "Notes on technical specifications"