transmissionsfaktor

Transmissionsfaktor, in English commonly referred to as transmission factor or transmittance, is a dimensionless quantity that measures the fraction of incident energy that passes through a material, optical element, or system. It is defined as the ratio of transmitted power (or irradiance) to the incident power (or irradiance): T = P_trans / P_incident (or I_trans / I_incident). Values range from 0 to 1 (often expressed as a percentage).

In optics and spectroscopy, the transmission factor describes how much light at a given wavelength passes through a medium. For a homogeneous, absorbing medium, Beer–Lambert law gives I = I0 e^{-αL}, so T = e^{-αL}, where α is the absorption coefficient and L is the path length. Real systems may also involve scattering, anti-reflective coatings, or multi-layer filters, causing the wavelength dependence of T to vary. Consequently, coatings and filters are characterized by a transmission spectrum T(λ).

Relations to other quantities: for non-scattering, non-emissive surfaces, transmittance T combines with reflectance R and absorptance A such that R + T + A ≈ 1. In radiative transfer and atmospheric science, the transmission factor is often written as T = e^{-τ}, with τ representing optical depth.

Applications and examples: optical windows and lenses, solar panels, camera filters, and atmospheric transmission studies rely on the transmission factor to predict how much light reaches a target. A clear pane might have T ≈ 0.9 in the visible, while specialized filters may transmit only a small fraction at certain wavelengths.

Notes: The term Transmissionsfaktor is used in German contexts, while transmittance (Transmittanz) is the common English counterpart.