The suitability of a pigment for inclusion in "cool" colored coatings with high solar reflectance can be determined from its solar spectral backscattering and absorption coefficients. Pigment characterization is performed by dispersing the pigment into a transparent film, then measuring spectral transmittance and reflectance. Measurements of the reflectance of film samples on black and white substrates are also used. A model for extracting the spectral backscattering coefficient S and absorption coefficient K from spectrometer measurements is presented. Interface reflectances complicate the model. The film's diffuse reflectance and transmittance measurements are used to determine S and K as functions of a wavelength-independent model parameter σ that represents the ratio of forward to total scattering. σ is used to estimate the rate at which incident collimated light becomes diffuse, and is determined by fitting the measured film reflectance backed by black. A typical value is σ=0.8. Then, the measured film reflectance backed by white is compared with a computed value as a self-consistency check. Measurements on several common pigments are used to illustrate the method.
BT - Solar Energy Materials and Solar Cells DA - 12/2005 DO - 10.1016/j.solmat.2004.11.012 IS - 4 LA - eng M1 - 4 N2 -The suitability of a pigment for inclusion in "cool" colored coatings with high solar reflectance can be determined from its solar spectral backscattering and absorption coefficients. Pigment characterization is performed by dispersing the pigment into a transparent film, then measuring spectral transmittance and reflectance. Measurements of the reflectance of film samples on black and white substrates are also used. A model for extracting the spectral backscattering coefficient S and absorption coefficient K from spectrometer measurements is presented. Interface reflectances complicate the model. The film's diffuse reflectance and transmittance measurements are used to determine S and K as functions of a wavelength-independent model parameter σ that represents the ratio of forward to total scattering. σ is used to estimate the rate at which incident collimated light becomes diffuse, and is determined by fitting the measured film reflectance backed by black. A typical value is σ=0.8. Then, the measured film reflectance backed by white is compared with a computed value as a self-consistency check. Measurements on several common pigments are used to illustrate the method.
PY - 2005 SP - 319 EP - 349 T2 - Solar Energy Materials and Solar Cells TI - Solar spectral optical properties of pigments—Part I: model for deriving scattering and absorption coefficients from transmittance and reflectance measurements VL - 89 ER -