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• TEM
• TFS
• TIR
• TIRM
• TM
• T-matrix method
• TOT
• transmissometer
• TSM

Transmissometer - an instrument for measurement of the transmission, T, of light by a medium. It consists of a light source emitting a unidirectional light beam and a detector (usually with a small acceptance angle) coaxial with that beam. The detector measures light power transmitted through a know thickness, z_m, of the medium that separates the light source and the detector. By using the Lambert law, expressed as T = exp(-cz_m), the transmission can be converted to the attenuation coefficient, c, of the medium. Hence another, frequently used name for the transmissometer is the attenuation meter. The magnitude of the acceptance angle of the detector is of no consequence for media that solely absorb light, given that there are no secondary light sources in the medium. However, it must be minimized when the transmission measurements are used, via Lambert law, in calculating the attenuation coefficient of a light scattering medium (see Lambert law: Scattering corrections, Radiative transfer equation and transmission measurement, and Attenuation coefficient: Measurement). [MJ]