The authors illustrate the use, and give the background theory of the operating principle of contrast-reducing visibility meters. The meter described in the article operates on the same principle as the Eastman visibility meter where the ceiling luminance is provided by the tank background itself. No lenses are used in the meter, the field is restricted by the aperture of the exit aperture or the length of the slits in the rotating discs which combine luminances at constant visual adaptation. The two 15 cm aluminised perspex discs can be moved relative to one another while they rotate on the same spindle at the same speed. The authors claim that rotating discs have several advantages as a means of combining luminances over other conventional optical methods. No transmitted light is lost through absorption or scattering. The prototype meter described has a circular field of view of about 5 degrees and a dynamic range of approximately 100. A refined version is commercially available. /TRRL/


  • English

Media Info

  • Features: Figures; Photos; References;
  • Pagination: p. 163-166
  • Serial:

Subject/Index Terms

Filing Info

  • Accession Number: 00145378
  • Record Type: Publication
  • Source Agency: Transport and Road Research Laboratory (TRRL)
  • Files: ITRD, TRIS
  • Created Date: Apr 13 1977 12:00AM