What does transmittance mean?
Transmittance is a technical term for the proportion of incident radiant energy that passes through a surface, material, or system. It is normally expressed as a fraction or percentage, making it a dimensionless measure rather than an amount of energy. The word is especially useful in optics, spectroscopy, solar-energy engineering, and the design of windows, lenses, filters, and photovoltaic equipment. For example, a coating with high solar transmittance allows much of the sun's radiant energy to pass through, whereas a darker coating may absorb or reflect more of it. Transmittance should not be confused with transmission, which names the broader process of passing energy or information along. It also differs subtly from transmissivity, which often refers more generally to a material's intrinsic capacity to transmit radiation. The term is formal and largely international in use.
nounThe ratio of the radiant energy transmitted through a surface to the radiant energy incident upon it, usually expressed as a fraction or percentage. The term is chiefly used in optics, spectroscopy, and solar-energy engineering.
- The proportion of incident radiant energy that passes through a surface, material, or other system, expressed as a fraction or percentage.
"The window's high solar transmittance allows most of the sunlight to pass into the greenhouse."
"The spectroscopist measured the spectral transmittance of the tinted glass at several wavelengths."
"Engineers selected the film for its high optical transmittance and low heat absorption."
The plural is possible but uncommon; transmittance is generally used as an uncountable term for a particular measurement.
"The researchers compared the transmittances of the different window coatings."
Transmittance is the invisible fraction of light that makes it through—essential for designing windows, sunglasses, filters, and solar panels.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does transmittance come from?
Transmittance was formed in English by adding the suffix -ance to transmit. Transmit ultimately comes from Latin transmittere, meaning “to send across,” with trans- indicating movement across or through and mittere meaning “to send.” The same Latin root produced related English forms such as transmission, transmitter, and transmissivity.
How transmittance is actually used
This is a formal technical term, especially common in physics, optics, spectroscopy, architecture, and solar engineering. In everyday usage, transmission is usually preferable when referring broadly to the act or process of sending or passing something.
Easily confused with transmittance
Transmission is the process of sending or passing something, whereas transmittance is the specific ratio of energy that passes through a surface.
Transmittance describes the transmission through a particular surface or layer, while transmissivity more often describes the intrinsic ability of a material to transmit radiation.