Lab test of glass SHGC, shading coefficient (SC), U-value & optical properties
We are a Singapore-based third-party test laboratory, providing lab test services of glass SHGC, shading coefficient (SC), U-value, and optical properties. Our lab is SAC-SINGLAS (ISO 17025) accredited and qualified for IGDB/CGDB submission. Our customers are from around 30 countries.
In our standard report, the following 10 important properties of glazing systems are reported:
- Visible light transmittance
- Visible light reflectance, front side
- Visible light reflectance, back side
- Solar energy transmittance
- Solar energy reflectance, front side
- Solar energy reflectance, back side
- Solar heat gain coefficient (SHGC)
- Shading coefficient (SC-value)
- Summer condition U-value
- Winter condition U-value
Upon your request, we can report nearly anything applicable to a glass:
- Spectral transmittance or reflectance, in IGDB format or in MS Excel format
- UV transmittance and UV rejection (UVR)
- Light-to-solar-gain (LSG) ratio
- Luminous efficacy
- Total solar energy rejection (TSER)
- CIE damage factor and skin damage factor
- Color rendering index (CRI)
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(+65) 6908 0126
Further readings
- Glass optical & thermal properties testing procedures – Single glazing
- Glass optical & thermal properties testing procedures – Double glazing
- Glass optical & thermal properties testing procedures – Partially fritted glazing
- How to test optical & thermal properties of glasses from existing buildings?
- How accurate are the glass optical & thermal test results?
- What are the differences between the NFRC, EN, and ISO glass optical & thermal test methods?
- 4 things to check when glass optical & thermal test results are different from manufacturer’s specifications
- Complete list of glass optical & thermal properties
- Low-e coating and glass optical & thermal performances
- Gas fill and double glazing unit (DGU) thermal performance
- Understanding OTM glass optical & thermal property test report
- Optical property testing for IGDB / CGDB submission
- Solar control window film and glass optical & thermal performances
- Daylight reflectance of glasses
- Glass color, color difference & color rendering
Online glass U-value, SHGC & shading coefficient calculator
Interested in performing your own glass U-value, SHGC & shading coefficient calculations? We have a user-friendly online calculator:
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SHGC, shading coefficient, and U-value are the 3 important glass thermal properties influencing building envelope energy efficiency.
Solar heat gain coefficient (SHGC)
The SHGC of a glass is defined as the fraction of solar heat falling onto the glass that enters a room.
Example: out of 500 W of solar heat falling onto a glass, 300 W enters a room, the glass SHGC = 300 W / 500 W = 0.60.
Apparently, the range of SHGC is between 0 and 1.
- In summer, glasses with small SHGCs are preferred, i.e. less solar heat enters a room and less energy is needed to cool the room;
- In winter, glasses with large SHGCs are preferred, i.e. more solar heat enters a room and less energy is needed to heat the room.
How to improve glass SHGC?
As shown above, SHGC consists of two components:
- Primary solar heat gain: the solar heat in its original solar radiation form.
- Secondary solar heat gain: the solar heat absorbed by a glass and further transferred to a room
In layman’s experience, when we stand next to a window in a sunny day:
- The sunlight falling onto us makes us feel warm. This is the primary solar heat gain.
- If we put our hand onto the glass, we feel the glass surface is hot. This is the secondary solar heat gain.
If our objective is to reduce SHGC, we need to:
- Lower the solar transmittance of the glass (in layman’s term, make the glass less transparent)
- Lower the solar absorbance of the glass (in layman’s term, make the glass more transparent or more reflective)
- Improve the insulation of the glass
The first and second points are contradictory. The SHGC of a glass with low transparency could be high.
A good example is that the SHGC of a black color opaque glass is actually quite large (could be around 0.20). Despite that it is opaque (zero direct transmission), its solar absorption is high, due to the black color.
Shading coefficient (SC-value)
The physical meaning of shading coefficient is exactly the same as SHGC. Shading coefficient is simply a SHGC scaled by 0.87.
The relationship between SHGC and shading coefficient is simple:
- SC = SHGC / 0.87
- SHGC = 0.87 x SC
Here, 0.87 is the nominal SHGC of a clear glass.
Shading coefficient is a relative scale in comparison with a clear glass. It is nowadays redundant to scale SHGC by 0.87. The industry still uses shading coefficient mainly for the purpose of backward compatibility.
U-value (thermal transmittance)
U-value is also called U-factor in the NFRC standards. Its full name is thermal transmittance.
The U-value of a glass is defined as the amount of heat transmitted through the glass in every 1 m2 of area and in every 1 K (1 °C) of temperature difference.
Example: 200 W of heat transmitted through a 10 m2 glass under 10 K (10 °C) of indoor/outdoor temperature difference, the glass U-value = 200 W / (10 m2 x 10 K) = 2.0 W/(m2K).
How to test SHGC, shading coefficient & U-value in the lab?
Please read our in-depth articles on the testing procedures:
Two instruments are used in glass testing: UV/VIS/NIR spectrophotometer and FTIR spectrometer.
UV/VIS/NIR spectrophotometer with 150 mm integrating sphere
OTM uses PerkinElmer Lambda 950 UV/VIS/NIR spectrophtometer with 150 mm integrating sphere for glass testing. It is the most commonly used instrument in glass testing labs. It measures the spectral transmittance and spectral reflectance of the glass samples in the wavelength range of 300 nm – 2500 nm.
For glass test, the instrument produces monochromatic light in the wavelength range of 300 nm – 2500 nm, at every 5 nm interval. An optical device called intergrating sphere is used to measure the light transmitted through or reflected by the test sample. Shown below is the interior of the integrating sphere. The bright spot in the center is the sampling beam.
FTIR with 10 degree specular reflection accessory
OTM uses PerkinElmer Spectrum Two with Pike10 10 degree specular reflection accessory. This is also a commonly used instrument in glass testing labs. This instrument measures spectral reflectance of a sample in the wavelength range of 5 micron to 25 micron. The results are used to calculate the emittance of the glass sample.
Sample sizes, from small to extra large
We are flexible in meeting your requirements. Listed blow are the possible glass sizes that we can measure:
- Minimum size: 25 mm x 25 mm
- Preferred size: 100 mm x 100 mm or smaller
- Maximum size without surcharge: 300 mm x 300 mm
- Maximum size with surcharge: 1 m x 1 m
Most customers provide us 300 mm x 300 mm samples, as this is a commonly used glass prototype size by the industry.
The accuracy is not dependent on sample size. However, it is very challenging to handle samples larger than 300 mm x 300 mm in the lab. Therefore, surcharge is applicable to samples larger than 300 mm x 300 mm.
It is possible to test glasses from existing buildings,
- For float glasses, it is recommended to cut the glass to a smaller size;
- For heat strengthened glasses, it is recommended to break the glass and test a few pieces of broken glasses;
- For tempered glasses, it is not possible to cut nor break them. They should be tested in their original size, subject to surcharge and the maximum size limit.
Sample types: you name it, we test it
We are able to test nearly all glass types. Listed below is only a partial list:
- Number of glass layers: single glazing, double glazing, triple glazing
- Glass coating: uncoated, with low-e coating (hard or soft), with low-reflection coating
- Laminated glasses: with PVB or SGP interlayers
- With add-on layers: with window film, with site applied coating, with ceramic frits
- Dynamic glazing: electrochromic glazing
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