AN ANALYSIS OF THICK-SAMPLE EFFECTS IN THE MEASUREMENT OF DIRECTIONAL-HEMISPHERICAL TRANSMITTANCE

Materials that are both thick and scatter light pose special problems in the measurement of transmittance. Traditional small-beam measuremen t techniques are not, in general, accurate when used with this type of material, due to the lateral displacement of light as it is transmitt ed. The technique of transmittance measurement using broad-area irradi ation can overcome this lateral-displacement problem, but it is subjec t to certain errors caused by non-uniformity of the irradiation. This paper examines the problems associated with transmittance measurements on thick and scattering samples in both small-area and broad-area irr adiation techniques and develops methods for determining the errors as sociated with each type of measurement.