What is a hot mirror?
A hot mirror is in essence a thin film coating applied to substrates in effort to reflect infra-red radiation either as a means to harness the reflected wavelengths for an application or to remove them from an application.
Hot mirrors are often misunderstood due to their name and understandably so. Judging by the name it would be reasonable to believe that these kinds of coatings reflect heat by reflecting the infrared spectrum. Along that line of thought it would seem that objects illuminated by visible light passing through a hot mirror would be cold, however that is not entirely the case.
It’s true that a hot mirror reflects a significant amount of heat through it’s effect on the infrared spectrum. There is still a measurable amount of heat generated through high energy visible light photons. These shorter length visible light photons actually carry more energy than those in the IR band. This means that if you implement a hot mirror and measured the temperature of the illuminated subject, you would still see a rise in temperature, albeit less of one than if you were to forgo the use of the hot mirror.
So this shows us that it’s not actually heat that they reflect, but the IR band and sometimes the UV band. As demonstrated by our HM-VS-1600 Hot Mirror which specifies that the average transmission is to be more than 85% from 425 to 675 nano-meters (nm) and the average reflectance is more than 90% from 750 to 1150 nm and 80% from 1150 to 1600 nm, but also indicates a high reflectance under 375 nm shown by the graph.
Another aspect of hot mirrors to be aware of is that most hot mirrors are colored a light yellow. This can adversely affect some applications that require the light to be as white as possible. For this reason ZC&R includes color neutral hot mirrors in our standard line.
For more information about Hot Mirrors and other Heat Control Coatings call 800-426-2864 or email us.
Abrisa Technologies is a recognized global supplier of high quality, fabricated glass components, optical thin film coatings, and custom glass solutions for a wide variety of industries. From our US based Abrisa Industrial Glass fabrication facility in Santa Paula, CA and our ZC&R Coatings for Optics division in Torrance, CA we serve diverse industries such as microelectronics and displays, semiconductor, military, automotive, aerospace, medical, biomedical and scientific R&D. We provide custom specialty flat glass and coating products for applications such as: flat panel display, touch and gesture recognition; visible to IR imaging and surveillance; entertainment, indoor and outdoor lighting; advanced instrumentation; and photonics.