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ASNT Level III Visual Testing, VT

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2.14 Types of Photometers<br />

2.14.1 Optical Bench Photometers<br />

Optical bench photometers are used for the calibration of instruments for<br />

illumination measurement. They provide a means for mounting light sources<br />

and photocells in proper alignment and a means for easily determining the<br />

distances between them. If the source is of known luminous intensity<br />

(candlepower), the inverse square law is used to compute illuminance,<br />

provided that the source-to-detector distance is at least five times the<br />

maximum source dimension.<br />

Charlie Chong/ Fion Zhang

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