Retroluminometer

a retroluminometer for measuring retroreflectivity of signs or markings at their actual point of use comprises (1) a source of alternating light; (2) optical means for both directing the alternating light onto a sign or marking that is to be tested and for transmitting light retroreflected by the sign or marking onto a panel within the retroluminometer; (3) a matrix of light-transmitting means arranged on the face of the panel; (4) photosensing means optically connected to the light-transmitting means and adjustable to sense and measure the light from different ones of the light-transmitting means, thereby measuring retroreflection at different angles of deviation from the axis of the light beam incident on the sign or marking; and (5) electric circuitry for presenting the photosensed light as a visually-readable measurement. The electric circuitry includes filtering circuitry for filtering out signals having a frequency different from that of the alternating source so as to eliminate the effect of ambient or extraneous light.

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Description
Patent History
Patent number: T987003
Type: Grant
Filed: Jul 31, 1978
Date of Patent: Oct 2, 1979
Assignee: Minnesota Mining and Manufacturing Company (St. Paul, MN)
Inventors: Norbert L. Johnson (Oakdale, MN), Michael J. Knowd (New Brighton, MN)
Application Number: 5/929,299
Classifications
Current U.S. Class: Of Light Reflection (e.g., Glass) (356/445); With Modulation (e.g., Flicker Beam) (356/447)
International Classification: G01N 2148;