On 1 July 2025, NIWA merged with GNS Science to become Earth Sciences New Zealand.

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 [ r.mckenzie@niwa.co.nz ]