Also total energy transmittance. Percentage of incident radiation that is allowed to pass through the glass as a whole. Serves to use free solar energy gains. In contrast, solar control glasses have a low g-value to avoid excessive heating in summer.

The g-value is also known as energy transmittance. It indicates how much energy can penetrate through the window from the outside to the inside. The value is given in percent. In general, the higher the g-value, the more solar radiation can be released into the room through the glazing as radiant heat. A high g-value can therefore achieve an equally high heat gain in the room. In the winter months this is more pleasant, but in summer the high g_value contributes to a significant heating of the rooms. This value is particularly important for passive houses that rely on solar gains (up to 60% of the heating energy).