The ratio of the solar heat gain passing through a glass unit referenced to the 3mm clear glass (defined value of 1.0). The lower the value, the less solar heat transmit through the glass, that being said, the shading ability is better. Generally, the shading coefficient of 3mm clear glass is 0.87.
Solar Heat Gain Coefficient
The Solar Heat Gain Coefficient (SHGC) is the percent of solar energy incident on the glass that is transferred indoors both directly and indirectly through the glass. The direct gain portion is the solar energy transmittance, while the indirect is the fraction of solar energy incident on the glass that is absorbed and re-radiated or transmitted through convection indoors. The SHGC ranges from 0 to 1 as a dimensionless(explanation 1.) number. Therefore, when the glass has a lower SHGC, it can resist the solar heat entering the room, effectively reducing the energy consumption of the A/C.
(explanation 1.)Dimensionless quantities in physics are those that require no unit.
Visible Light Transmittance
Visible Light Transmittance (VLT) (green building>=0.5) describes the percentage of visible light (approximately 390 to 780 nanometers within the solar spectrum) transmitted through the glass. It is determined by the glass color and thickness. Clear glass has 75% to 92% VLT; colored glass has 14% to 85% VLT.
Visible Light Reflectance
Visible Light Reflectance (VLR) (green building<=0.25) is a ratio of visible light that is reflected from a glass building materials when illuminated by the light. The higher the VLR, the light reflectance problems could be greater.
The blocking rate of ultraviolet light. When the value is higher, the better the UVR is.
Angular Optical Properties
The characteristic parameters are determined for quasi-parallel, almost normal radiation incidence. For the measurements, the samples shall be irradiated by a beam whose axis is at an angle not exceeding 10° from the normal to the surface. The angle between the axis and any ray of the illuminating beam shall not exceed 5°.