Chapter 53 - Optical Properties Measurement of Dry and Wet Transparent Materials

Abstract

The directional-hemispherical and the directional-conical transmittances and the bidirectional transmittance distribution function of a single clear glass (SG) plate, a low-emissivity coated glass (LEG) plate, a low-density polyethylene (LDPE) film, and a diffusive co-extruded polyethylene (DPE) film were determined in the laboratory. Experiments were carried out on the dry materials, as well as on the materials covered with condensate, for normally incident radiation. When dry, both glass plates behaved as highly transmitting non-scattering materials. The presence of condensate drops on the glass plates caused a strong forward scattering, since only 19% of the transmitted radiation was regularly transmitted. The total radiation transmitted through the glass plates, 89% for SG and 85% for LEG, was not changed significantly by the condensate. Even in the dry state, the plastic films showed forward scattering due to their surface roughness. About 90% of the incident radiation passed through the LDPE film, half of which was scattered. For the DPE film, 78% was transmitted, 80% of which was scattered. The presence of condensate enhanced the forward scattering of both plastic films. About 22 and 7% of the transmitted radiation (67 and 62%) passed regularly through the LDPE and the DPE film, respectively.