Preparing samples for luminance contrast test

Related services Luminance contrast

The luminance contrast test is always in terms of two samples in a pair, typically one bright color sample and one dark color sample. There are two scenarios for sample preparation:

  • Side-by-side flat surfaces
  • TGSI studs on a flat surface

Side-by-side flat surfaces

For side-by-side flat surfaces, two flat-panel samples need to be submitted. Shown below is an example:

The preferred sample size is 100 mm x 100 mm or slightly smaller. The maximum sample size is 300 mm x 300 mm. Only 1 pair of samples (2 pieces) are needed and it is optional to provide additional samples as the backup.

TGSI studs on a flat surface

For Tactile Ground Surface Indicator (TGSI) studs on a flat surface, it is possible to submit the samples as either integrated samples or loose samples.

Integrated samples

Shown below is an example of an integrated sample of TGSI studs on a flat surface:

The preferred sample size of the integrated sample is 100 mm x 100 mm or slightly smaller. The maximum size is 300 mm x 300 mm. Only 1 sample is needed and it is optional to provide additional samples as the backup.

Loose samples

It is possible to submit TGSI studs and flat surface samples separately, without fixing them. Shown below is an example.

It is recommended to provide 2 – 5 loose TSGI stud samples.

For the flat surface sample, the preferred sample size is 100 mm x 100 mm or slightly smaller. The maximum size is 300 mm x 300 mm. Only 1 sample is needed and it is optional to provide additional samples as the backup.

The difference between NFRC winter and summer U-values

Related services Glass optical & thermal properties

Listed in the table below are the standard NFRC winter and summer environmental conditions:

Environmental conditionNFRC winterNFRC summer
Outdoor air temperature-18 °C32 °C
Outdoor wind speed
5.5 m/s
(26 W/m2K)
2.75 m/s
(15 W/m2K)
Outdoor sky temperature-18 °C32 °C
Outdoor sky emissivity11
Indoor air temperature21 °C24 °C
Indoor convectionASHRAE/NFRC inside modelASHRAE/NFRC inside model
Indoor room temperature21 °C24 °C
Indoor room emissivity11

These are the standard environmental conditions defined in the NFRC standards and widely used by the industry. It is possible to define local environmental conditions and use them in a specific region.

In the US, the NFRC winter U-value is used (called U-factor and with the imperial unit).

In Singapore, the NFRC summer U-value is typically used, and, in our test reports, both the winter and summer U-values are reported.

For most glasses, the summer condition U-value is smaller than the winter condition Value. The main reason is that the outdoor wind speed in the summer conditions is lower and it results in a lower outdoor side convective heat transfer rate.

Online glass U-value, SHGC & shading coefficient calculator: V2.1.0

Related services Glass optical & thermal properties

We’ve just upgraded our online glass U-value, SHGC & shading coefficient calculator to V2.1.0, with the feature of argon gas concentration specification added.

It is now possible to vary the argon gas concentration to study its impact on glass U-value. The default argon concentration is 95%. Please click the screenshot below to access this online calculator and also read this article on the relationship between gas fill and double glazing unit (DGU) thermal performance.

Acceptance criteria for solar reflectance index (SRI)

Related services Solar reflectance index (SRI)

We are often asked, “can the SRI of my material pass the requirement?”. This post aims to answer this question.

There are no universal acceptance criteria for SRI. In practice, there could be 3 types of acceptance criteria:

There might be other types of acceptance criteria depending on your objective (e.g. if you want to certify your products under SGBP Certification, SGBC has their own requirements).

Project-specific SRI requirements

Please check with the buyer (e.g. architect, consultant or owner) for the project-specific SRI requirements.

USGBC LEED SRI requirements

Please refer to this page for the requirements in LEED.

Singapore Green Mark requirements

Please refer to this document for the requirements in Green Mark (please search “SRI” in the PDF document).


The information listed above may be outdated. Please check with your LEED or Green Mark consultant for the latest requirements.

Additionally, 3 SRI results are presented in our test reports (low-wind, medium-wind, and high-wind, as shown below). If it is not explicitly stated in the requirement, the medium-wind SRI result shall be used in the evaluation by default.

KSJ MG6-F1 gloss meter

Related instruments KSJ gloss meters

For general applications, KSJ MG6-F gloss meter is recommended. Listed below are the key specifications:

  • Angle: single-angle (60°)
  • Range: 0 – 199.9
  • Resolution: 0.1 GU
  • Beam size: 10 mm × 20 mm

More information is available in the following documents:

For more details, please expand one of the blocks below.


The gloss meter uses 1 piece of AA-size battery. The typical battery life is around 58 hours (alkaline battery; without backlight and BlueTooth).

Basic operations

There are just 3 simple steps to perform gloss measurement:

  1. Power on
  2. Calibration
  3. Gloss measurement

1. Power on

Long press the “ON/OFF” button to switch on the gloss meter

2. Calibration

There is a calibration board in the base holder of the gloss meter (shown above). Mount the gloss meter to the base holder and buckle it properly.

Short press the “Calibration” button. While the “CA” symbol is flashing, short press the “Calibration” again. The “CA” symbol disappears and the gloss meter is calibrated.

3. Gloss measurement

Take out the gloss meter from its base plate. Attach the measurement port (at the bottom of the gloss meter) to the surface to be measured. The gloss result is displayed on the screen, without pressing any button.

Good practices

The following good practice practices are recommended:

  • Keep the calibration board and the lens in the measurement port clean.
  • Re-calibrate the gloss meter frequently.
Smartphone controlled gloss measurement

It is possible to perform online gloss measurement with a smartphone (both Android and iOS) via BlueTooth connection and store the gloss measurement results in the smartphone.

Refer to the user’s manual for the details.

Can daylight reflectance be tested with ASTM E903 only?

Related services Daylight reflectance

As suggested by the title of ASTM E903:

Standard test method for solar absorptance, reflectance, and transmittance of materials using integrating spheres

ASTM E903 is for the testing of solar absorptance, reflectance, and transmittance, but not daylight reflectance directly. The procedures of spectral reflectance measurement with integrating spheres are described in ASTM E903 in detail, but it is still insufficient to get the daylight reflectance results with ASTM E903 only.

Therefore, at OTM, ASTM E903 is supplemented with other test methods in daylight reflectance testing:

  • For general materials: ASTM E971 and CIE 130
  • For glass materials: NFRC 300

Please refer to our daylight reflectance page for more information.

Small and light class C pyranometer: LPPYRA-Lite

Related instruments Pyranometers

Delta Ohm just released a new pyranometer product LPPYRA-Lite with the following features:

  • Spectrally flat class C according to ISO 9060:2018
  • With thermopile sensor
  • Output type: mV (default) or 4-20 mA (on request)

The weight of the pyranometer is only 150 g. It is suitable for small PV power plant monitoring or general solar radiation measurements. Please click the pyranometer photo below for the datasheet.


How to get window film optical & thermal properties with different glass substrates?

Related services Glass optical & thermal properties

Typically, window film optical & thermal properties are tested with 3 – 6 mm clear or low-iron glasses as the substrate. Window film properties obtained with such high transparency glass substrates are more appropriate for product performance rating purposes.

In real buildings, window film products can be attached to all possible glass substrate types, such as tinted glasses, low-e coated glasses, laminated glasses, and double glazing units (DGUs). There are two methods to get window film optical & thermal properties with different glass substrates, as described below.

Option 1: direct physical test method

With the direct physical test method, the window film shall be attached to the actual glass substrate to be used. The whole glass system with window film is tested as usual.

This method is recommended for most applications, with a small number of glass substrate types.

Option 2: physical test + calculation method

With the physical test + calculation method, the following glasses need to be tested (based on the NFRC 304 method):

  1. Window film on a reference glass substrate (typically a 3 – 6 mm clear or low iron glass)
  2. The reference glass substrate (without window film)
  3. Other glass substrates

With the test results of glasses 1 & 2, the window film only optical data can be calculated. The window film only optical data can then be added to all glass substrates tested in step 3 to get the combined glass with window film optical & thermal properties.

This method is recommended for product development applications, with a large number of glass substrate types.