The steps 2 – 4 in single glazing glass testing are followed in the IGDB optical property testing:

• Step 2. Spectral reflectance measurement with FTIR
• Step 3. Spectral transmittance/reflectance measurement with UV/VIS/NIR
• Step 4. IGDB file generation with IGDB@OTM

The details of the IGDB data file format are available in this document and some example data files are available on this page.

In the example data file presented above:

• Rows 1 – 15 are the header and the following rows are important:
  • Row 2: glass thickness in mm
  • Row 3: glass thermal conductivity in W/(m⋅K)
  • Row 5: glass emissivity (when left blank, the emissivity is auto-calculated from the optical data provided below)
• From row 16 are the optical data
  • Column 1: wavelength
  • Column 2: spectral transmittance
  • Column 3: front side spectral reflectance
  • Column 4: back side spectral reflectance

The IGDB format file can be imported to the LBNL Optics software. Refer to this blog post for the operations.

By default, the visible light transmittances of the samples are measured. The visible light reflectances are measured, only when the visible light transmittances of all samples are less than 0.01.

The steps described in Appendix C of AERC 1.1 are used and the instrument used at OTM is a UV/VIR/NIR spectrophotometer with 150 mm integrating sphere. The spectral transmittance/reflectance in the 380 nm – 780 nm is measured, and the visible light transmittance/reflectance is calculated from the spectral data.

The homogeneity calculation essentially results in the following:

• The mean visible light transmittance/reflectance
• The tolerance (TvT) or confidence interval (CI) of the 95% confidence interval of all results
• The ranks of all results

For the ranks of all results, the results are ranked from the smallest to the greatest, with a rank from 1 to 18. The two results at the center of a result set (i.e. the 9th and the 10th ranked results) are compared with the mean result to get the closer one. The sample with the closer result is then selected as the representative sample for the more detailed optical property testing.

1) Newly developed materials: by default, the 18 samples of a material shall be from 3 different manufacturing lots, with 6 samples from each lot. For newly developed materials, it is permitted to test 6 samples from 1 single lot for the initial homogeneity testing and test the remaining 12 samples later.

2) Materials in a material product family: a simplified homogeneity testing process is available if there are multiple materials in a product family. It is permitted to select two materials from the product family, one with light colour and one with dark colour (if there are multiple openness factors, one with the lowest openness factor and one with the highest). If the homogeneity tolerances of the two selected materials are within the homogeneity limits specified in AERC 1.1, it is possible to proceed to the optical property testing with a single sample for all materials. Otherwise, homogeneity testing needs to be performed for all materials.

3) Materials under the recertification process: if the homogeneity tolerance of a material meets the requirements lists in AERC 1.1, it is possible for the material to be recertified, with some written affirmation and without re-testing. If the requirements are not met, the optical properties of a single new sample need to be re-tested. If the visible light transmittance/reflectance result is within the homogeneity tolerance, all material optical properties are updated to the new sample’s results (without homogeneity testing). Otherwise, the homogeneity testing needs to be re-performed and a new representative sample needs to be selected again and tested accordingly.

As illustrated above, for the incident light (the black color ray) transmitted/reflected by a surface, there are two components:

• Specular transmission/reflection (the blue color ray): the transmission in the same direction of the incident light or the mirror-like reflection in the direction opposite to the incident light
• Diffuse transmission/reflection (the red color rays): the general transmission/reflection scattered in all directions

The sum of the specular transmission/reflection and diffuse transmission/reflection is the total transmission/reflection.

The instrument, UV/VIS/NIR spectrophotometer with 150 mm integrating sphere, can be configured to measure the direct-hemispherical and diffuse spectral transmittance/reflectance in the 300 nm – 2500 nm wavelength range. The direct-hemispherical transmittance/reflectance is equivalent to the total transmittance/reflectance.

A special method is described in Appendix E of AERC 1.1 on fabric material thermal emissivity and IR transmittance measurement. The method is also described in a technical note by the emissometer manufacturer.

The details of the CGDB interim file format is available in this document.

In the example data file presented above:

• Rows 1 – 13 are the header and the following rows are important
  • Row 2: sample thickness in mm
  • Row 3: sample thermal conductivity in W/(m⋅K)
  • Row 4: sample IR transmittance
  • Row 5: sample thermal emissivity
• From row 14 are the optical data
  • Column 1: wavelength
  • Column 2: front side specular spectral transmittance (Tf_n-dir)
  • Column 3: front side diffuse spectral transmittance (Tf_n-dif)
  • Column 4: back side specular spectral transmittance (Tb_n-dir)
  • Column 5: back side diffuse spectral transmittance (Tb_n-dif)
  • Column 6: front side specular spectral reflectance (Rf_n-dir)
  • Column 7: front side diffuse spectral reflectance (Rf_n-dir)
  • Column 8: back side specular spectral reflectance (Rb_n-dir)
  • Column 9: back side diffuse spectral reflectance (Rb_n-dif)

For the row header in row 13, below are the meanings of the abbreviations:

• T: transmittance
• R: reflectance
• f: front side
• b: back side
• n-dir: normal-to-directional, i.e. specular
• n-dif: normal-to-diffuse, i.e. diffuse