Infra-red (IR) is the major part of solar radiation that contributes to heat. IR is absorbed by the interior materials and skin, making them warmer. The lower the IRT, the less heat is transmitted through the window. You may also find the term spectrally selective being referred to as a film with high VLT and low IRT.
The percent of Infra-Red that is reflected by a glazing system
The percent of total ultraviolet light that is rejected from passing through a glazing system.
For safe driving and to meet the legal regulations, RTA stipulates a 70% VLT for the front windscreen and 2 front windows and 50% for the rear windscreen and the 2 rear side windows. Professional window film installation centres have an equipment called a Tint Meter to measure the VLT, after the film has been installed, to demonstrate that it meets RTA's compliance. Always ensure that the VLT reading you get for VLT compliance is the window's VLT after the film has been installed and not the film's VLT specs alone.
The percent of total visible light that is reflected by a glazing system.
Total Solar Energy Rejected (Tser) is the combination energy rejection of the visible light, infra-red and ultra violet. A high Tser reading need not necessarily mean a high heat rejection as it could also mean a high visible light rejection. Therefore a darker film gives a better Tser rejection than that of a lighter film. To ensure that a film has a good heat rejection performance, it is best to look at the infra-red rejection specification.
To distinguish, a high performance film from one that is low, also look for the Total Solar Absorption (Asol). To effectively cut off heat, solar radiation has to be 'reflected' rather than be 'absorbed'. A high Asol would simply mean that solar heat is 'absorbed' by the film and once the film reaches its thermal capacity, the 'absorbed' heat is re-radiated back into the car cabin. High Asol may also cause unnecessary thermal stress on the windows due to heat build-up.'
The percent of incident solar radiation that is absorbed by a glazing system.
The ratio of incident solar radiation that directly passes through a glazing system.
The ratio of solar heat gain through a glazing system to the solar heat gain of a single lite double-strength glass. A measure of degree of efficiency of a glazing system to control solar energy. The lower the shading coefficient number, the better the solar shading qualities of the glazing system.
The overall coefficient of heat transfer by conduction equals the reciprocal of R value. The lower the U-Value, the better the insulating qualities of the glazing system.
A measure of the ability of a product to reflect long wave radiant energy. The lower the emissivity, the better the insulating qualities of the glazing system.
The ratio of daylight transmission to solar heat transmission which passes through a glazing system. This is determined by dividing the visible light transmittance by the shading coefficient. The higher this number the better it indicates how much of the transmitted solar energy is useful visible light rather than heat.
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