Patent ID: 6376829
Filing Date: 2002-04-23
Classification: G01B,G01N

Abstract:
A method of inspecting surface irregularities of a transparent plate comprising:irradiating a beam of light from a light source toward a surface of the transparent plate at an angle of incidence ranging from 60 to 89 degrees; polarizing said beam of light from said light source by a polarizing element disposed between the light source and the transparent plate so that said beam of light from said light source is incident on the surface of the transparent plate as one of a P-polarized light beam and an S-polarized light beam; projecting a reflected image of said beam from the surface of the transparent plate on a screen; and inspecting irregularities of the surface of the transparent plate on the basis of said reflected image projected on the screen; wherein said angle of incidence of said S-polarized light beam and said angle of incidence of said P-polarized light beam are in the range from; 85 to 89 degrees and 87 to 89 degrees when a visible ray transmittance of said transparent plate is 90% or more and less than 100% respectively; 84 to 89 degrees and 87 to 89 degrees when said visible ray transmittance is 80% or more and less than 90%, respectively; 83 to 89 degrees and 87 to 89 degrees when said visible ray transmittance is 70% or more and less than 80%, respectively; 81 to 89 degrees and 86 to 89 degrees when said visible ray transmittance is 60% or more and less than 70%, respectively; 78 to 89 degrees and 84 to 89 degrees when said visible ray transmitted is 50% or more and less than 60%, respectively; 72 to 89 degrees and 82 to 89 degrees when said visible ray transmittance is 40% or more and less than 50%, respectively; 60 to 89 degrees and 75 to 89 degrees when said visible ray transmittance is 30% or more and less than 40%, respectively; and 60 to 89 degrees and 60 to 89 degrees when said visible ray transmittance is less than 30%, respectively.