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Method of measuring light levels and device for implementing this method

  • US 5,323,226 A
  • Filed: 06/26/1992
  • Issued: 06/21/1994
  • Est. Priority Date: 06/27/1991
  • Status: Expired due to Term
First Claim
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1. A method of monitoring exterior light levels in a zone of approach to a tunnel in which vehicles are moving, for adjusting levels of minimum illumination inside the tunnel, comprising:

  • measuring light levels in the zone of approach to the tunnel by using a photo-sensitive cell which is axially recessed in a tube relative to an end of the tube, the tube having a longitudinal axis which intersects said cell and on which said cell is centered and having first structure effectively defining a cone having an apex on said axis at said cell, coaxial with said tube and increasing in diameter towards said end of said tube;

    whilelimiting the quantity of light rays entering into said cone at said end of said tube by placing effectively across said end of said tube a second structure having a preselected pattern of light transmissivity which pattern is centered on said axis.

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