Tinted Glass, What is tinted glass, Why use tinted glass

Tinted glass speaks to what is tinted glass and why use tinted glass.

It is used to help with deal with building solar heat gain. Solar heat buildup can be a problem in buildings with large areas of glass, especially during the warm part of the year. Fixed sun shading devices outside the windows are the best ways of blocking unwanted sunlight, but glass manufacturers have also developed tinted glasses that reduce glare and cut down on solar heat gain.

The transparency of glass to visible light is called its visible light transmittance. It is measured as the ratio of visible light that passes through the glass relative to the amount of light striking the glass. Clear glasses have visible light transmittance in the range of 0.80 to 0.90, meaning that 80 to 90 percent of the visible striking the glass passes through to the building interior. The remaining 10 to 20 percent is either reflected or absorbed by the glass and converted to heat.

By tinting, its visible light transmittance is reduced. This glass is made by adding small amounts of selected chemical elements to the molten glass mixture to produce the desired intensity and hue of colour in grays, bronzes, blues, greens and golds. The visible light transmittance of commercially available tinted type ranges from about 0.75 in the lightest tints to 0.10 for dark gray.

The overall reduction in solar heat gain is often significantly less, however because the solar radiation absorbed by the glass and converted to heat must go somewhere and a substantial portion of it is conducted or reradiated to the interior of the building.

To evaluate the effectiveness of glass in reducing heat gain from solar radiation, a measure called the solar heat gain coefficient (SHGC) is used. It is the ratio of solar heat admitted through a particular glass to the total heat energy striking the glass. SHGC accounts for the solar radiation that passes through glass, as well as for heat that is conducted or radiated into the space due to heating of the glass itself.

Clear glasses have solar heat gain coefficients ranging from about 0.90 to 0.70, depending on the clarity and thickness of the glass. Solar heat gain coefficients for tinted glasses range from about 0.70 to 0.35, meaning that these glasses allow 70 to 35 % of the solar heat energy striking the glass to pass through.

Generally speaking, for buildings dominated by a heating load, glass with a high SHGC is desirable to take advantage of passive solar heat gains. In buildings dominated by cooling, glass with a low SHGC is preferable to minimize unwanted solar heating.

Shading coefficient, a measure similar to SHGC, is an older measure of reduction in solar heat gain that has been mostly replaced by SHGC.

Visible transmittance and solar heat gain coefficient can be combined to determine the light to solar gain (LSG) ratio, a useful measure of the overall energy conserving potential of glass. The LSG ratio is defined as the visible light transmittance divided by the solar heat gain coefficient. A glass with high LSG admits a relatively large portion of visible light in comparison to the amount of solar heat admitted, combining the greatest daylight potential with the least least solar heating potential.

Green and blue tinted glasses tend to have high LSG rato values, while those of bronze, gold and gray tints tend to be lower.

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