Testing

Can daylight reflectance test be performed on curved surfaces?

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Specular reflection follows the law of reflection, which states that the angle of incidence is equal to the angle of reflection, measured with respect to the local surface normal.

For a flat surface, the surface normal is uniform across the entire area. As a result, incident light is reflected in a single, well-defined direction, allowing the specular component to be reliably captured by the instrument.

For a curved surface, the surface normal varies from point to point. According to the law of reflection, the direction of reflected light therefore also varies across the surface. Instead of a single direction, the specular reflection is spread over a range of angles.

Daylight reflectance instruments measure reflection within a defined geometry. For curved surfaces, part of the specular reflection falls outside this geometry. As a result, the instrument misses part of the specular component, leading to an underestimation of the specular daylight reflectance.

In practice:

  • For curved surfaces with a strong specular component, the measurement error can be significant. Results should therefore be interpreted with caution.
  • For curved surfaces with a weak specular component, the impact is negligible, and measurements may still be acceptable

In summary, daylight reflectance testing can be performed on curved surfaces, but the accuracy, particularly for the specular component, may be limited.

Is Solar reflectance index (SRI) applicable to translucent materials?

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Related services Solar reflectance index (SRI)

The concept of Solar Reflectance Index (SRI) is not directly applicable to translucent materials, such as fabrics and membranes. Please refer to this post for a simple way to check if a material is translucent using mobile phone flashlight.

This limitation is explicitly reflected in the title of ASTM E1980:

ASTM E1980: Standard Practice for Calculating Solar Reflectance Index of Horizontal and Low-Sloped Opaque Surfaces

The scope clearly specifies opaque surfaces only. Therefore, applying ASTM E1980 to calculate the SRI of translucent materials is not technically valid.

This post explains the key challenges involved in determining the SRI of translucent materials and discusses practical workarounds.

The challenges

There are three main challenges when attempting to determine the SRI of translucent materials:

1. Solar energy transmission

Solar radiation interacting with a material follows the relationship:

solar reflectance + solar transmittance + solar absorptance = 1

For opaque materials, solar transmittance = 0, so solar absorptance can be derived directly from solar reflectance.

However, for translucent materials:

  • Both solar reflectance and solar transmittance need to be measured
  • Solar absorptance can only be determined after accounting for transmission

This adds complexity to the characterization process.

2. Infrared radiation transmission

Thermal emittance is commonly measured using ASTM C1371. However, this method assumes the material is opaque.

For translucent materials:

  • Infrared radiation may pass through the sample
  • The measured emittance can be influenced by the substrate or background behind the material

As a result, the measurement may not represent the intrinsic property of the material itself.

3. SRI calculation model

The SRI calculation defined in ASTM E1980 is based on a heat balance model that assumes:

  • No solar transmission
  • Surface-only energy exchange

Because translucent materials allow radiation to pass through:

  • The underlying heat transfer model becomes invalid
  • The calculated SRI does not accurately represent real thermal behavior

Practical workarounds

Although SRI cannot be directly applied, there are practical approaches to characterize translucent materials:

1. Make the system opaque

The translucent material can be mounted onto an opaque substrate to form a composite system. This prevents solar and infrared radiation transmission
Standard SRI measurement methods can then be applied

Please note that the result represents the SRI of the system, not the standalone material.

2. Test the material by assuming it is opaque

In some cases, translucent materials may be tested using the same procedures as opaque materials, effectively assuming that the material is opaque during the SRI measurement.

This approach can still provide meaningful results when the material has low solar transmittance, such that only a small portion of the incident solar radiation passes through the sample. Under these conditions, the measured SRI may still serve as a useful practical indicator of surface thermal behaviour.

However, the transmitted solar component is not properly accounted for in the measurement. Therefore, results obtained using this approach should be interpreted with caution, particularly for materials with significant solar transmission.

3. Measure optical properties separately

It is still possible to characterize the optical behaviour of translucent materials by measuring solar reflectance, solar transmittance, and solar absorptance separately.

This approach provides a more complete physical understanding of the material. The measured optical properties can then be used in thermal models, other than the SRI model, for further analysis.

PBS880D BAROsense barometric pressure transmitter with static port

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Related instruments pressure transmitters

Shown below is a PBS880D BAROsense barometric pressure transmittance with a static port:

The PBS880D BAROsens is a barometric pressure transmitter designed for accurate atmospheric pressure measurements.

It has a standard measuring range of 800 to 1100 mbar. An alternative version is available with a range of 600 to 1100 mbar. The device provides a 4–20 mA output, with additional output options such as 0–10 V available upon request.

The unit is equipped with a static port, which minimizes the influence of dynamic pressure caused by wind, making it suitable for open-field measurements. The static port comes with a mounting bracket and can be installed on poles with diameters of up to 50 mm.

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BAROsense PBS880 barometric pressure transmitter

BAROsense PBS880 barometric pressure transmitter

Special note on laminated glass with embedded coating

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Laminated glass with embedded coating refers to laminated glass in which the coating is in direct contact with the interlayer.

The example below illustrates this configuration, where the low-e coating is located on surface #2 and is in contact with the interlayer.

As clearly documented in THERM 7 / WINDOW 7 NFRC Simulation Manual (page 8-111), the standard calculation method cannot be applied to this type of glass construction.

This is because when a coating is in direct contact with the interlayer, its performance can change compared to when it is exposed to air, and these changes are not fully reflected in the standard calculation models.

For laminated glass with embedded coatings, the most reliable approach to obtaining thermal and optical performance data is to fabricate representative samples and carry out physical measurements.

In practice, calculation methods are sometimes applied to estimate performance data for such glass configurations. However, due to the limitations noted in the NFRC documentation, results obtained in this way may not accurately represent actual performance.

How to measure daylight reflectance with a portable colour meter?

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Related services Daylight reflectance

It is possible to measure the daylight reflectance of a surface using a portable colour meter. For best results, a portable colour meter equipped with an integrating sphere is recommended.

The preferred measurement settings are:

  • Illuminant: D65
  • Observer: 10° standard observer
  • Colour space: Yxy

Many colour meters provide two measurement modes:

  • SCI (Specular Component Included): The Y value obtained in this mode is equivalent to the total daylight reflectance.
  • SCE (Specular Component Excluded): The Y value obtained in this mode is equivalent to the diffuse daylight reflectance.

The difference between the SCI and SCE Y values is equivalent to the specular daylight reflectance.

Q: Can the results measured with this method be used for BCA submission?

A: No. The Building and Construction Authority (BCA) requires testing in accordance with ASTM E903. Portable colour meters do not meet this requirement and therefore cannot be used for BCA submissions.

Q: How accurate are the results?

A: Accuracy depends largely on the performance of the instrument.

As a general guideline:

  • For colour meters based on the spectrophotometric method, the total daylight reflectance results are reasonably accurate, especially for neutral colours.
  • The diffuse and specular daylight reflectance results are typically less accurate, since the integrating spheres in most portable colour meters are relatively small.

Despite these limitations, the measurements remain useful for preliminary assessments and internal evaluations.

Q: What if my colour meter measures only L*ab?

Some online tools are available to convert L*ab results into Yxy colour values. One example is: Convert Lab to Yxy

HD208 wall-mount compact temperature & humidity data logger

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Related instruments Temperature & humidity

Shown below is a HD208L.1NTV wall-mounted compact temperature & humidity data logger:

The instrument offers the following features:

  • Temperature & humidity monitoring: the temperature, humidity, and dew point results are alternately displayed on the LCD screen
  • Data logging function: continuously records environmental conditions over time
  • Large internal memory: with a 5-minute logging interval, the instrument can store over 1 year of data
  • Long battery life: the internal battery can last for more than 2 years
  • Automatic report generation: generates PDF reports and CSV result files with a single click
  • Compact in size: Weighs approximately 150 g, making it ideal for wall-mounted installations

The instrument is ideal for monitoring indoor environmental conditions. Upon request, it can be supplied with an ISO/IEC 17025 accredited calibration report.

Related instruments

HD208 compact wall-mounted temperature & humidity data logger

HD208 compact wall-mounted temperature & humidity data logger

Can the testing fee be reduced by skipping some glass optical property results?

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The following table of results is presented in our glass optical & thermal property test report:

We sometimes receive questions about whether the testing fee can be reduced by excluding some optical property results.

Please refer to this page for information on the testing procedures for glass optical and thermal properties. The optical properties serve as intermediate results in determining thermal properties. The solar heat gain coefficient (SHGC) and shading coefficient (SC) are derived from 5 sets of raw data on spectral transmittance/reflectance. All other results are calculated from this same data set without requiring additional testing.

Therefore, even if some optical properties are omitted, the testing procedures remain unchanged, and the testing fee will not be reduced.

Outdoor WBGT monitoring station with large water tank and cloud service

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Related instruments Thermal comfort & microclimate, Wireless & web data loggers

OTM WBGT Monitoring App
We’ve extended the functionality of the Senseca WBGT monitoring instrument with the OTM WBGT Monitoring App.

You can now receive timely WBGT alerts and monitoring results directly via WhatsApp — on your phone or computer — along with daily, weekly, or monthly summary reports.

Read more here for full details.

Shown below is an HD35EDWWBGT outdoor WBGT monitoring station with a large water tank and cloud service.

Data logger and WBGT probes
Base unit with 4G connectivity

The features include:

  • Meets MOM workplace WBGT monitoring requirements
  • Safe for outdoor installations, with solar radiation shield for the temperature probe
  • Large water tank (500 cc), with expected autonomy longer than 1 month in Singapore
  • Data logger is battery power, with 2-year typical life
  • Base unit is with 4G connectivity and supporting cloud reading (note: local 4G subscription required, 230 VAC power supply required, base unit cannot be exposed to rain)

Shown below are the software and cloud portal screenshots:

Shown below is a photo taken from a site:

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HD35EDWWBGT integrated station for WBGT monitoring

HD35EDWWBGT integrated station for WBGT monitoring

HD35AP4G base unit with 4G connectivity

HD35AP4G base unit with 4G connectivity

Can glass optical & thermal property test be performed on shattered tempered glass pieces?

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We frequently receive inquiries about whether optical and thermal property testing can be performed on shattered tempered glass pieces.

However, our instruments require a minimum sample size of 1 inch (25 mm) to obtain accurate results. Since shattered tempered glass pieces are typically smaller than this, it is impractical to conduct the tests on such small fragments.

For tempered glasses, the most practical solution is to remove a full and intact piece of glass from the building for testing, as detailed on this page.