A measure of the ability of a surface to absorb and re-radiate energy; in simple terms, emissivity is the fraction of long wave infra-red energy remaining after reflection back to the source. A low value reduces the rate of heat flow through the glazing; window film can reduce emissivity of glazing to less than 0.4. Example: An emissivity of 0.33 means that 67 % of the long wave infra-red energy is reflected back to the source.
This is the percentage reduction of visible light transmitted through glass with film installed, compared to clear 3mm glass.
IR Heat Rejection
Infra-Red Heat Rejection - Infrared (IR) light is the part of the EM spectrum that people encounter most in everyday life, although much of it goes unnoticed. It is invisible to human eyes, but people can feel it as heat. Some window films, often know as spectrally selective films, reduce the heat from the IR part of the spectrum whilst maintaining a virtually invisible appearance.
In most cases this is the thickness of the base material excluding the thickness of the adhesive.
Non Reflective – These are films that have no or very little metallisation in them, therefore they tend to absorb more heat as they are unable to reflect it. With these products you should be more careful on which glass types you apply non reflective films to.
Pressure Sensitive – This is the most common type of adhesive used on window films. It has a tacky residue and provides faster adhesion to the glass than a water-activated adhesive.
A ratio of solar heat gain through a window with window film installed compared to the heat gain on a standard glass pane under the same testing conditions. The lower the shading coefficient the more efficient the window film in rejecting solar energy.
Solar Energy Absorbed
This is the ratio of the amount of solar energy that is absorbed by the glass to the amount of total solar energy falling onto the glass.
Solar Energy Reflected
This is the ratio of the amount of solar energy that is directly reflected off the glass to the amount of total solar energy falling onto the glass.
Solar Energy Transmitted
This is the ratio of the amount of solar energy that is passing through the glass to the amount of total solar energy falling onto the glass.
Total Solar Energy Rejected – This is the total amount of heat that is rejected by the window film. The higher the percentage the more amount of heat that is rejected away. This energy is rejected either by reflecting or absorption by the glass.
Ultra-Violet (UV) Rejected
The portion of Ultra Violet light that is rejected from entering the building by the filmed glazing expressed as a percentage.
The U value is a measure of the rate of heat transfer through the glazing (or other building material) and is given in units of W/m².K. A method of calculating the U value of glazing is given in EN 673 “Glass in building. Determination of thermal transmittance (U value). Calculation method”. The portion of Ultra Violet light that is rejected from entering the building by the filmed glazing expressed as a percentage.
Visible Light Transmission – The total amount of light that passes through the window film. Usually the darker the film, the lower the percentage, the more heat it rejects.
Water Activated – This is a non-tacky adhesive which must be applied with water to activate the adhesive. The curing time tends to be longer with water activated adhesives and it takes longer to adhere to the glass.