Total energy transmittance
The total energy transmittance is the sum of radiation transmission ST and secondary heat emission Qi to the inside.
ST + Qi = g-value
Besides the U-value, the total energy transmittance is the most important parameter for glazing. It indicates how much of the external solar energy ultimately reaches the interior of the room. For optimum passive use of solar energy, the g-value should be as high as possible and as low as possible for optimum sun protection.