In transmission, waves are transmitted through a medium
, whereas in
reflection they are reflected by a medium and in absorptionthey are
absorbed.The magnitude of transmission is given as the trans
mittance.This is the quotient of the transmitted energy, that is, the energy transmitted by the medium, and the energy in front of the medium.
The transmittance, or transmission coefficient, is denoted by T, or the Greek tau, and is a dimensionless number between 1 and 0. If the entire energy is transmitted by the medium, the transmittance is 1; if no energy is transmitted, the value is 0. There is a direct mathematical relationship between the transmittance, reflection factor and absorption
coefficient: the sum of the three factors is 1.
In optical systems, the transmittance represents the light transmission of the material.