Glossary of Terms
Solar Control Window Films
Absorbance - The fraction of incident radiation that is absorbed.
Ashrae – Abbreviation for American Society of Heating, Refrigerating and Air-conditioning Engineers.
Conduction – Process of heat transfer through a material from a warm surface to a cool surface.
Conduction Factor – Difference in the “U-values” before and after film application to glass multiplied by 24 hours / day. This factor is used in calculating heating energy savings.
Convection – heat transfer by the movement of fluid or air.
Emissivity – Measure of ability of a surface to emit room temperature radiant heat energy. Also a measure of the ability of the surface to reflect room radiant energy since, for window systems, the emissivity and the reflectivity of room radiant energy add up to unity. A low emissivity means a high reflectivity of room radiant energy.
Glare Reduction – Ratio of the difference in visible transmission of the glass before and after installing film. It is expresses as a percentage and is determined by the respective visible transmission values of the glass with and without film.
Heat Gain – Transfer of heat from outside to inside. Both heat loss and heat gain are measured in terms of fuel consumption required to maintain a comfortable indoor temperature.
Heat Loss – Transfer of heat from inside to outside by means of conduction, convection and radiation through all surfaces of the building.
Heat Loss Reduction – Ratio of the difference in heat loss through the glass after installing film; to the heat loss through the glass with no film. It is expressed as a percentage and is determined by the respective “U” Values of the glass with and without film.
“R” Value – A measure of resistance to heat gain or loss (insulative ability). “R” Values, rather than thickness, can be compared for different materials.
Shading Coefficient – Ratio of solar energy entering through a window compared to that which enters through a window of clear 1/8” (3mm) double strength sheet glass. Solar energy which enter includes both that which is transmitted directly through the window and that portion of the energy absorbed in the window that is transferred to the interior.
Solar Heat Reduction – Ratio of the difference in total solar energy entering before and after installing film on the glass to that entering through the glass with no film. Expressed as a percentage, it is determined by the respective shading coefficients of the glass with and without film. This considers both solar energy transmitted and re-radiated absorbed solar energy.
Solar Heat Gain Coefficient - SHGC measures how well a product blocks heat caused by sunlight. The SHGC is the fraction of incident solar radiation admitted through a window, both directly transmitted, and absorbed and subsequently released inward. SHGC is expressed as a number between 0 and 1.
The lower a window’s SHGC, the less solar heat it transmits.
Total Solar Energy – When solar radiant energy strikes the exterior surface of a window, the energy is reflected , absorbed and / or transmitted as defined above. The total of the three parameters must add up to 100 percent.
Total Solar Energy Absorbed – Ratio of solar energy absorbed by the window and converted to heat in the window to total solar energy impinging on the window. Typically expressed as a percentage.
Total Solar Energy Transmitted – Ratio of solar energy transmitted directly through the window where it is absorbed by interior surfaces to the total solar energy impinging on the exterior window surface. Typically expressed as a percentage. It does not include heat reradiated from energy absorbed in glass.
Total Solar Energy Reflected – Ratio of the difference in solar energy entering the interior (including both transmitted and
re-radiated energy ) through glass and film to total energy impinging on the window.
“U” Value – measurement used in determining the ability of different structural components (such as windows) to conduct heat. The “U” Value of a window is measured by the number of watts that will pass through each square metre of area per degree Celsius (W / m2 / oC) from one side of the window to the other. “U” Values can tell you how well your windows will hold in heated or cooled air. The lower the number, the better.
Visible Light Reflected – Visible light is defined as the portion of the solar energy spectrum under average daylight conditions that is visible to the human eye. Values given are based on the response of the human eye. The ratio of that which is reflected away from the surface of the window to that impinging on it is called the percentage of visible light reflected.
Visible Light Transmitted – A ratio of the human eye weighted average daylight that is transmitted through the window to that which is incident upon the window.
Visible Radiation – The spectrum containing radiation with wavelengths in a narrow band from about 400 nanometres (violet) to the 750 nm (red). At the earth’s surface, about half the solar energy is in the visible range.
Definitions supplied courtesy of the
Window Film Association of Australia and New Zealand
