An apparatus for measuring specular reflectance of a sample is provided including a light source for transmitting a beam of light at an angle of incidence onto a surface of a sample; a polarizing filter comprising a wire grid that avoids a need for collimation of the incident beam of light; a sample holder for mounting the sample; and a detector assembly for detecting a beam of light which is specularly reflected from a surface of the sample; wherein the sample holder and detector assembly are mounted for relative movement, such that the light source, the detector assembly and the sample holder are relatively positionable for a specularly reflected component of a transmitted light beam to be detected for different angles of incidence of the light beam.