A method of and apparatus for identifying the presence of thin photocatalytic (PCAT) coatings on glass surfaces. An apparatus is disclosed that can determine whether a PCAT coating (which may comprise titanium dioxide, for example) having a thickness of less than about 100 .ANG. is present on the surface of a substrate such as glass. The apparatus may measure the reflectance of electromagnetic energy (such as light energy) at the surface of a substrate using energy at selected wavelengths or wavelength ranges. The apparatus may determine reflectance values for PCAT coated surfaces of any thickness, as well as for uncoated surfaces.