DAYLIGHT TRANSMITTANCE: The percentage of visible light that a glazing transmits through glass.
SHADING COEFFICIENT (SC): Measures the total solar heat gain through the glazing compared to 1/8″ clear glass under the same conditions. It includes both the solar energy transmitted directly plus any absorbed solar radiation that is re-radiated as heat into the interior. The number ranges from 0.0 to 1.0. Standard insulating glass has a SC of .81 The lower the shading coefficient, the lower the solar heat gain.
RELATIVE HEAT GAIN (RHG): A number which represents the amount of heat entering a building due to both solar radiation and conductive/convective heat gain. The total heat flow through the glass for a specific set of conditions. This value considers indoor/outdoor temperature differences and the effect of solar radiation (Btu’s/hr./ft 2 ).
SOLAR HEAT GAIN COEFFICIENT: The percentage of Solar Energy either directly transmitted or absorbed and then re-radiated into the building.
LOW EMISSIVITY COATINGS: Coatings applied which allow shortwave energy to be transmitted through glass, but reflect long wave infrared radiation. The lower the emissivity, the lower the resultant U-value.
U-VALUE: Measures the heat loss or gain due to differences between indoor and outdoor air temperatures (Btu’s/hr./ft2). The U-value equals one divided by the R-value (U=1/R). The lower the U-value, the better the insulating performance.
R-VALUE: Measures the insulation effectiveness of the window. The R-value equals one divided by the U-value (R=1/U). The higher the R-value, the better the insulating performance.
PYROLYTIC LOW-E: Glass with a coating, either visually reflective or low emissivity, applied at high temperatures and fired into the glass surface during float glass production.
SOFT COAT LOW-E: Glass with a coating applied in a secondary process at ambient temperature within a vacuum chamber.
HEAT MIRROR™: A high performance soft-coat low-e sputtered directly on an optically clear substrate then suspended within the airspace of an insulated glass unit.
| EFFICACY FACTOR: The ratio of Visible Transmission (Tvis) to Shading Coefficient (SC): |
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A simple ratio of Light to Heat. The higher the number, the more light per amount of heat. A low number means that either it is a dark glass or a lot of heat gets through. A superior, spectrally-selective glass will have a K> 1.0 This may also be called Light to Heat Ratio (LHR) or Coolness Factor.
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