Glass optical & thermal properties

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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)
An example test results page with SHGC, shading coefficient (SC), U-value and optical properties reported.

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(+65) 6908 0126

Further readings

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:

More information

Expand one of the blocks below for more information.

What are SHGC, Shading coefficient & U-value?

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?

The heat transfer mechanism of solar heat gain coefficient and shading coefficient

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:

Test methods

Select the right test standards

Are you aware that there are 3 widely used international standards for glass testing, namely NFRC / ISO / EN methods?

If your glass manufacturer’s specifications are according to NFRC method and your test reports are according to ISO method, you are actually doing a meaningless apple-to-orange comparison.

Essentially, when talking about U-value & shading coefficient, it is critical to know the test method used. A glass with shading coefficient of 0.25 according to NFRC method and another glass with the same shading coefficient according to ISO could be two completely different glasses.

OTM is able to conduct test according to all major test method. Let’s be serious in test method selection, for better quality control.

NFRC method

NFRC method is the most widely used test method. Glass manufacturers from USA, Singapore & China always produce their glass specifications according to the NFRC method:

  • ANSI/NFRC 100-2020 Procedure for determining fenestration product U-factors
  • ANSI/NFRC 200-2020 Procedure for determining fenestration product solar heat gain coefficient and visible transmittance at normal incidence
  • NFRC 300-2020 Test Method for Determining the Solar Optical Properties of Glazing Materials and Systems
  • NFRC 301-2020 Standard Test Method for Emittance of Glazing Products

This method is SAC-SINGLAS accredited.

EN method

EN method is the second most widely used test method after NFRC method. Glass manufacturers from Europe produce their glass specifications according to the EN method:

  • EN 410:2011 Glass in building – Determination of luminous and solar characteristics of glazing
  • EN 673:2011 Glass in building – Determination of thermal transmittance (U value) – Calculation method

ISO method

ISO method is not commonly used by glass manufacturers. However, ISO method is the blueprint of most national standards (for example, JIS standard in Japan is based on the ISO method):

  • ISO 9050:2003 Glass in building — Determination of light transmittance, solar direct transmittance, total solar energy transmittance, ultraviolet transmittance and related glazing factors
  • ISO 10292:1994 Glass in building — Calculation of steady-state U values (thermal transmittance) of multiple glazing 

Other methods

On special circumstances, we can also perform test according to specific national standards, e.g. JIS R 3106 and JIS R 3106.


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.

UV/VIS/NIR spectrophotometer
UV/VIS/NIR spectrophotometer

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.

Detailed view of the integrating sphere of the UV/VIS/NIR spectrophotometer
Interior of the integrating sphere

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.

FTIR spectrometer
FTIR spectrometer

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.
Small size samples
9 pcs of 75 mm x 75 mm small samples. This size is preferred by the lab, as they are easy to handle
A standard size 300 mm x 300 mm sample
A 300 mm x 300 mm DGU sample. This size is preferred by customers, as it is commonly used by the industry for glass prototyping
An over-sized samples
An oversized tempered glass sample (0.7 m x 1.7 m)
A piece of small sample, from a broken heat strengthened glass
For heat strengthened glass, it is possible to break it and test a small piece only

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
A single glazing sample, with hard low-e coating
Single glazing (with hard low-e coating)
A double glazing unit, with soft low-e coating and laminated inner pane
Double glazing (with soft low-e coating and laminated inner pane)
A tripe glazing system prototype, without spacer
Triple glazing (prototype without spacer)
A clear glass with window film
Clear glass with window film
A glass with site-applied coating
Glass with site-applied coating
A glass with ceramic frits
Glass with ceramic frits
Extended results

More than U-value & shading coefficient

It is often required to provide extended performance data, in addition to the standard result set. We can report almost all extended results.

Below is a partial list of the extended results:

  • UV transmittance (UVT) & UV rejection (UVR)
  • IR rejection (IRR)
  • Total solar energy rejection (TSER)
  • Color (transmitted or reflected)
  • Color rendering index (CRI)
  • Luminous efficacy (LE) & light to solar gain (LSG) ratio
  • Skin damage factor
  • CIE damage factor

Refer to the complete list of glass optical & thermal properties for more details.

Cost, lead time & procedures


Please contact us for the testing fee.

Lead time

The typical lead time is 5 working days.


Our sales personnel will guide you through the necessary procedures.

Upon your request, the following three documents will be emailed to you:

  1. Official quotation
  2. Standard terms & conditions
  3. Test request form

The client needs to return us the following documents:

  1. Official purchase order (PO) or signed quotation
  2. Completed test request form

The client needs to submit the test samples to our laboratory. The test will commerce as soon as possible after the test samples are received.


Frequently Asked Questions (FAQs):

Q1. Are your test reports recognized internationally?

Yes. The lab is SAC-SINGLAS accredited. Our test reports carry the “ilac-MRA” and “SAC-SINGLAS” marks and they are recognized internationally. Our lab is also eligible for IGDB and CGDB submissions.

Q2. How accurate are your results?

The measurement uncertainties are stated in the test reports. They are typically ±0.010 for optical properties (e.g. SHGC, VLT) and ±0.10 W/(m2K) for U-value.

Q3. What are the meanings of the results in your report?

We have technical articles explaining the testing procedures and in this article the meanings of the test results are explained in detail.

Q4. What are your test sample requirements?

 We can test nearly all glazing types: monolithic, coated, laminated, with window film, with ceramic frits, double glazing unit and others.

Q5. How much is the cost?

Please contact us for the price.

Q6. How long is the lead time?

You will receive the results within 5 working days, after sample submission.

Q7. What are the procedures?

Please contact us with your sample size and quantity. We will provide you the relevant documents and the sample submission instructions accordingly.

Q8. Can I visit your lab?

Sure, we welcome you to visit our lab to understand our testing procedures and assess our quality system. Please contact us if you wish to visit our lab.

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