Jun 19 2014
Transmittance is the fraction of incident light of a specific wavelength which passes via a sample. It is also defined as the ratio of the incident power (P) to the resulting power (P0).
T = P/P0
Transmittance is a numerical value between zero, i.e., all light is absorbed, and one i.e., no light is absorbed. Percent transmittance (%T) can be obtained by multiplying the definition by 100%.
%T = P/P0 x 100
Percent transmittance ranges between 100%, i.e., all light is transmitted and 0% i.e., no light is transmitted. When the transmission spectrum is plotted, 100% is at the top of the plot while 0% is at the bottom. However, the baseline of the graph is at 100% as no signal is present.
Visible transmittance is the amount of visible light passing through a glazing material. It is greatly influenced by glass coatings, the number of panes and the type of glazing. Visible transmittance of glazing ranges from over 90% for uncoated water-white clear glass to less than 10% for high reflective coatings. UV transmittance, on the other hand, is influenced by heavier elements of glass such as lanthanum, titanium, niobium, barium and lead. The infrared transmittance is mainly affected by the OH content in the atomic surrounding.
Sources and Further Reading