A safe and inexpensive, hand-held reflectometer has been developed to provide reflectivity measurements near one wavelength for mirrors in the field and laboratory. The principle used is: the specular reflection of a parallel collimated light beam from an LED, focused onto a large area pin diode, so that the beam throughout is always intercepted. The beam is chopped and filtered by an electronic circuit to make it immune to fluorescent and other ambient light conditions except bright sunlight. The response is shown to be linear and the 100 point can be calibrated by an extension tube which brings the beam in line with the detector, or a fresh aluminium mirror can be used. The small power drain enables the calibration to be retained.
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