Light transmittance (tL)

The light transmittance tL indicates what proportion of the visible radiation passes perpendicularly through the glass. Visible radiation is understood here to mean wavelengths from 380 nm to 780 nm, relative to the brightness sensitivity of the human eye. Only about half of the solar radiation energy is visible sunlight. Put simply, this means that the higher the tL-value, the more light penetrates into the room from outside. Light transmittance is expressed as a percentage and is reduced by, among other things, glass thicknesses, glass reflection and glass coatings.

The light transmittance of thermal insulation glazing, for example, is 0.76 (76%).