Selectivity is a factor that looks at the relationship between Visible Light Transmittance (VLT) and Solar Energy Transmittance – ie. Solar Heat Gain Coefficient (SHGC).
Where strong Solar Control is required (eg. Commercial buildings and warm-hot climate Residential buildings), a lower SHGC value is needed - representing less heat from the sun entering inside the building, and therefore, more heat from the sun being blocked. There is a correlation between lower SHGC and lower VLT in glass products. This is because the darker the glass, the more heat from the sun is blocked from entering through it, and the darker the glass, the lower the VLT.
While we need significant Solar Control performance for some buildings and climates, we must be mindful of the impact of the correlating low VLT as there are health and comfort concerns associated with a lack of natural light and we also do not want to work, or live, inside dark buildings.
For any building that requires a low SHGC, rather than purely accept a glass product that meets that SHGC value, it is important to investigate what that glass product looks like aesthetically as well as how much VLT it allows through. This is especially relevant whenever tinted glass, dark tinted glass, dark coatings, or coated tinted glass are considered.
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