Hot & Cold Mirrors

• Reflects infrared, transmits visible/UV light (hot mirrors) or reflects visible, transmits infrared (cold mirrors)
• Key specs: cut-off wavelength, bandwidth, angle of incidence
• High transmission/reflection coefficients for optimal performance
• Applications: projectors, fiber optics, lasers, cameras
• Available in various sizes and specifications

2 products

Major Specification of a Cold & Hot Mirror

The major specifications of hot & cold mirrors include:

  • Cut-off wavelength: The wavelength at which the transmission or reflection of light changes abruptly. For example, a hot mirror may have a cut-off wavelength of 700 nm, meaning that it reflects light above 700 nm (infrared) and transmits light below 700 nm (visible and ultraviolet).
  • Bandwidth: The range of wavelengths that are transmitted or reflected by the filter. For example, a cold mirror may have a bandwidth of 400-700 nm, meaning that it reflects light within this range (visible) and transmits light outside this range (infrared and ultraviolet).
  • Angle of incidence: The angle between the incoming light beam and the normal to the filter surface. The angle of incidence affects the performance of the filter, as different angles may result in different cut-off wavelengths and bandwidths. For example, a hot mirror may have a cut-off wavelength of 700 nm at normal incidence (0 degrees), but a cut-off wavelength of 650 nm at 45 degrees.
  • Transmission and reflection coefficients: The percentage of light that is transmitted or reflected by the filter at a given wavelength and angle of incidence. For example, a hot mirror may have a transmission coefficient of 90% at 500 nm and a reflection coefficient of 10% at 800 nm.

What’s the difference between hot and cold mirror?

The main difference between hot and cold mirror is that they have opposite effects on the spectrum of light. A hot mirror reflects infrared radiation (heat) and transmits visible and ultraviolet light, while a cold mirror reflects visible light and transmits infrared radiation. This means that a hot mirror produces a cooler beam of transmitted light, while a cold mirror produces a warmer beam of reflected light.

Applications of Hot Mirror & Cold Mirror

Hot and cold mirrors are useful for heat control and wavelength selection in optical systems. Some examples of applications are:

  • Projectors: A combination of hot and cold mirrors can be used to filter out unwanted UV and IR light from the light source, such as a metal halide bulb, and produce a bright and pure beam of visible light for projection.
  • Fiber optics: A combination of hot and cold mirrors can be used to isolate visible light from UV and IR light, as optical fiber is damaged by these wavelengths.
  • Lasers: A combination of hot and cold mirrors can be used to overlay two beams of different wavelengths, such as an invisible IR laser for cutting tissue and a visible laser for guiding the scalpel.
  • Cameras: A hot mirror can be used to block IR light from reaching the sensor, as IR light can cause color distortion and reduce image quality.

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