Solar simulators are light sources with specialized characteristics that make them similar to natural sunlight in quantifiable ways. At minimum, solar simulators resemble natural sunlight in their specific spectral match, their low spatial non-uniformity, and their low temporal instability.

Solar simulators are described in terms of their classification in the format: “Class XYZ” in which the position of the letters is fixed:

Class XYZ: X represents spectral match: the output irradiance is measured in several wavelength intervals. The percentage output irradiance in each interval is measured, and any one interval with the lowest classification match determines the total ranking (e.g. if all intervals but one are Class A, and one is Class B, the spectral match is Class B).

Class XYZ: Y represents spatial non-uniformity: the output irradiance is measured at a set of evenly spaced points throughout the target area. The upper and lower range of those points determines the spatial non-uniformity classification. It is important to note that this parameter uses broadband measurements and does not break down the light into wavelength intervals.

Class XYZ: Z represents temporal instability: the output irradiance is measured over a specified time interval and the upper and lower range of these measurements determines the temporal instability. It is important to note that the relevant time scale for these parameters was determined with regard to silicon photovoltaics, so other applications may have different (including less stringent) requirements.

Classifications of A+, A, B, and C for each parameter are defined by internationally recognized standards. Class A+ is primarily intended for use in calibration laboratories and is not considered necessary for manufacturing and qualification testing.

Other features that are not included in the standard classification but which may nonetheless be important in specific applications include:

Collimation: the degree to which the rays of light are parallel. Due to the extreme distance between the sun and the earth’s surface, natural sunlight is highly collimated. In many applications, this is not highly relevant, but in others, especially space applications, it may be important.

Air Mass Filter: Depending on the specific conditions the solar simulator is intended to simulate, different spectral conditions will need to be adhered to. For example, greater UV output and greater overall intensity is required when simulating the environment just outside of the earth’s atmosphere (AM0) rather than simulating the environment present outdoors, on the ground, and at mid-latitudes (AM1.5G).

Terrestrial or Space Solar Simulator: Depending on the specific conditions the solar simulator is intended to simulate, different spectral conditions will need to be adhered to. For example, greater UV output and greater overall intensity is required when simulating the environment just outside of the earth’s atmosphere (space solar simulator or AM0) rather than simulating the environment present outdoors, on the ground, and at mid-latitudes (terrestrial solar simulator or AM1.5G). AM1.5D and AM1.0D are less common air masses used in terrestrial solar simulators.