How does a dichroic work?

Understanding How a Dichroic Filter Works

Dichroic filters, also known as dichroic mirrors or dichroic beamsplitters, are optical components that selectively pass light of a small range of colors while reflecting other colors. They are constructed using thin film technology, which involves depositing many layers of dielectric materials onto a glass or other transparent substrate. The unique properties of dichroic filters come from the interference of light waves as they pass through or reflect off these multiple layers.

Key Principles Behind Dichroic Filters

  • Interference: The core principle behind dichroic filters is optical interference. When light waves reflect off the different layers of the filter, they interfere with each other. This interference can be constructive or destructive, amplifying certain wavelengths of light while canceling others out.
  • Thin Film Coating: The precise control over which wavelengths are reflected and which are transmitted is achieved through the use of thin film coatings. These coatings are made up of many layers of dielectric materials, each with a different refractive index. The thickness and sequence of these layers determine the filter's spectral properties.
  • Angle of Incidence: The performance of a dichroic filter can also depend on the angle at which light strikes its surface. Changes in the angle of incidence can shift the wavelengths that are transmitted or reflected, making the filter's response angle-dependent.

Applications of Dichroic Filters

Dichroic filters have a wide range of applications in various fields, including:

  • Lighting: In stage lighting and architectural lighting, dichroic filters are used to create vibrant, saturated colors that do not fade over time.
  • Photography: They are used in some camera systems to split light into different color channels, improving color separation and image quality.
  • Scientific Instruments: Dichroic filters are essential components in fluorescence microscopy and spectroscopy, where they are used to separate different wavelengths of light for analysis.


Dichroic filters are sophisticated optical components that exploit the principles of interference and thin film technology to selectively transmit and reflect light. Their ability to precisely control light makes them invaluable in a variety of applications, from enhancing the visual appeal of lighting designs to improving the accuracy of scientific measurements.

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