Photo-multiplier tube based portable photometer
min. 0.01 cd/m² | PR-1500 Photo Research, Inc.

Over four decades ago, PhotoResearch invented "spot" photometry when it introduced the Spectra Screen Brightness Meter for the motion picture industry. A few years later, a military customer inquired about measuring aircraft instrument panels and Photo Research produced the first Spectra Spotmeter microphotometer

The PR-1500 Spotmeter is a sensitive, versatile photomultiplier-tube photometer that can measure luminance(photometric brightness) at any distance from 1¾ inches (44 mm) to infinity without the need for accessory lenses or changes in calibration. The PR-1600 SpectraSpot, a silicon-cell photometer/radio meter, is designed for applications requiring the inherent stability and near infrared response of the silicon cell, without requiring the higher sensitivity of photo multiplier tubes.