Effective aperture

The position of the diffuser's entrance aperture needs to be known for accurate calibration. Because the diffuser has a hemispherical shape the effective entrance aperture is not exactly located at the front surface.

Experiments with the lamp at 1.5 m and 0.5 m show that according to the inverse square law the location of the effective entrance aperture is 1.4 mm (±1mm) behind the front surface of the diffuser.


Info, questions and remarks, contact: Richard McKenzie 

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Emeritus Researcher – Atmospheric Radiation