Transmittanssia

Transmittanssia, or transmittance, is a measure of how much incident radiation passes through a material or medium. It is a dimensionless quantity, often expressed as a ratio or as a percentage, and is denoted by T. If I0 is the intensity of the incoming radiation and It is the transmitted intensity after passing through the sample, then T = It / I0. In spectrophotometry and optics, transmittanssia describes how transparent a substance is for light at a given wavelength.

Transmittanssia depends on several factors. Wavelength is crucial because many materials absorb specific wavelengths more than others. The thickness or path length of the sample and the concentration of absorbing species directly affect T. Surface reflections at interfaces can reduce transmitted light, and scattering within a medium can alter the amount of light that emerges in the forward direction. In simple, non-scattering, homogeneous media, transmittanssia is related to the absorption coefficient α by T = e^(-αx), where x is the path length. When absorbance is measured, transmittanssia and absorbance A are connected by T = 10^(-A) and A = -log10(T).

In practical measurements, transmittanssia is often obtained as a transmittance spectrum across wavelengths using a spectrophotometer. A blank or reference sample is used to calibrate the instrument. In solid samples, it is common to distinguish direct (unscattered) transmittanssia from diffuse transmittanssia, especially in scattering media like Turbid solutions or powders.

Applications of transmittanssia include evaluating optical coatings and lenses, characterizing filters and solar cells, and studying atmospheric or optical-path transmission. In many contexts, transmittanssia, together with reflectance and absorptance, helps describe how a material interacts with light.