Expert in Optical & Thermal Measurement Solutions
We’ve just released our Q3/2021 OTM Insights newsletter, with the main article “Low-e coating and glass optical & thermal performances“.
Please click the image below to read the newsletter. For the past issues, please proceed to our branding & publications page.
On customers’ requests, we can provide the IGDB format files of the glass samples tested by us. Shown below is a screenshot of an IGDB format file:
The IGDB format file can be imported into LBNL Optics and WINDOW for further calculations.
For more detailed operations of the two software tools, please visit the respective help documents. The steps of importing user IGDB format file into LBNL Optics is described below.
Use “Datebase” -> “Create new user database” to create a new user database file *.mdb.
When asked “Do you want to switch to this new (empty) database?”, click “Yes”.
Use “File” -> “Import Text File(s)…” to import the IGDB format file.
We are pleased to introduce our online luminance contrast calculator (V1.0.0, first version). Click the screenshot below to access this online calculator.
The calculation principle of this calculator is similar to the online total daylight calculator. The luminous reflectances of the two sRGB colors selected are calculated with color space conversion. The luminance contrast is then calculated from the two luminous reflectance results.
We are pleased to introduce our online total daylight reflectance calculator (V1.0.0, first version). Click the screenshot below to access this online calculator.
The calculator simply converts an sRGB color (common in screen displays and websites) to a CIEXYZ color, whose Y component is equivalent to the total daylight reflectance of the color (refer to this Wikipedia article for more details).
This calculator calculates total daylight reflectance only and it cannot calculate diffuse and specular daylight reflectances, as the latter two components are dependent on surface finishing, but not on surface color.
The conversion is a theoretical conversion and does not introduce conversion errors. In practice, one needs to manually match a physical color with screen displayed color. This manual process introduces some errors. Nevertheless, this online tools is still useful in estimating the total daylight reflectance of color samples.
BCA requires that, for roof surfaces with greater than 20° inclination angle, the total daylight reflectance shall be less than 20% (What is daylight reflectance?). The table below lists 4 colors (grey, red, green, and blue) with close to 20% total daylight reflectance.
If your color is brighter than the 4 colors (except blue color, read the explanation below the table), it is possible that it cannot meet the 20% requirement.
| Color type | Color value | Total daylight reflectance | Color display |
|---|---|---|---|
| Grey | RGB (123, 123, 123) Hex (#7B7B7B) | 0.198 (19.8%) | |
| Red | RGB (248, 0, 0) Hex (#F80000) | 0.200 (19.8%) | |
| Green | RGB (0, 144, 0) Hex (#009000) | 0.199 (19.9%) | |
| Blue | RGB (0, 0, 255) Hex (#0000FF) | 0.072 (7.2%) |
Human eyes are less sensitive to blue and red colors, but more sensitive to green and grey colors. In the table above, the total daylight reflectance of the most saturated blue color in the sRGB color space is only with 7.2% of total daylight reflectance.
A measurement system was integrated by OTM for on-site glass optical & thermal property monitoring. The system uses off-shelf sensors and wireless data loggers and can be easily deployed for 24×7 glass performance monitoring projects.
The system consists of two indoor measurement systems (reference room vs. test room) and one outdoor measurement system. Shown below are the system schematics.
The following quantities are measured:
The system is for glass optical & thermal performance monitoring only. The results are qualitatively correlated to glass visible light transmittance and solar energy transmittance.
However, it is not possible to quantitatively evaluate glass optical & thermal properties rated under standard conditions (e.g. visible light transmittance, U-value, and shading coefficient) from the monitoring results. If such quantities are required, please consider our laboratory glass testing service.
The following instruments from Delta Ohm were used in the monitoring system:
Necessary mounting accessories were included. The instruments can be conveniently installed on-site in less than 1 hour. Shown below is a photo of the outdoor side instruments in the demo installation.
Shown below is a screen capture of some monitoring results (in the wireless data logger control software).
An in-house software can be used to automate the data processing part, as shown below.
Shown below are some sample results:
We are able to measure material yellowness index and whiteness index according to ASTM E313-20. The measurement part is the same as our usual material color measurement.
The spectral reflectance data in the 380 nm – 780 nm range are used in the calculation. Our in-house software Color@OTM has been upgraded for automated calculation.
As the spectral range is included in the daylight reflectance test and solar reflectance index (SRI) test, it is possible to re-use the spectral data collected in the two tests for yellowness index and whiteness index calculation, without re-testing.
We’ve just released our Q2/2021 OTM Insights newsletter, with the main article “complete list of glass optical & thermal properties“.
Please click the image below to read the newsletter. For the past issues, please proceed to our branding & publications page.
As shown above, solar heat gain coefficient (SHGC) consists of two components:
The primary solar heat gain component is just the solar energy transmittance of the glass.
The secondary solar heat gain component is calculated as the solar energy absorptance of the glass multiplied by its inward flowing fraction. The solar heat absorbed by the glass causes a temperature increase of the glass. The absorbed solar heat flows to either the indoor side or the outdoor side. The fraction flowing to the indoor side is the inward flowing fraction.
For example, for a glass with 30% solar energy transmittance, 20% solar energy absorptance and 0.25 inward flowing fraction:
In summary:
SHGC = primary solar heat gain + secondary solar heat gain
Primary solar heat gain = Solar energy transmittance
Secondary solar heat gain = solar energy absorptance × inward flow fraction
Solar energy transmittance and SHGC are different. Solar energy transmittance is the primary solar heat gain component of SHGC only. The SHGC of a glass is always greater than its solar energy transmittance.
We have a detailed article on the testing procedures of partially fritted glass optical & thermal properties. For partially fritted glasses, the daylight reflectance property concerns many customers. This article aims to present some opinions from us on the daylight reflectance of partially fritted glasses.
If you are a textualist and adhere to the texts strictly, partially fritted glasses are obviously made of glass, as the word “glass” appears in the name, and you should stop reading this post from here.
If you are not a textualist and open to some discussions, below are some explanations on the differences between glass and non-glass materials in terms of optical characteristics.
There are 3 types of material surfaces, in terms of optical characteristics:
In our opinion, conventional glasses and glasses with ceramic frit are distinct in optical characteristics. For a partially fritted glass, it is more reasonable to classify its clear part as glass material and classify its fritted part as non-glass material.
Optical characteristics:
For such materials:
Examples:
Optical characteristics:
For such materials:
Examples:
Optical characteristics:
For such materials:
Examples:
Luminance contrast is a measure of the difference in brightness of two surfaces. People with vision impairment prefer higher luminance contrast to identify TGSIs (tactile ground surface indicators).
The surface brightness is measured by its luminous reflectance. The luminous reflectance of a surface is the fraction of visible light reflected by the surface and it is equivalent to the daylight reflectance, visible light reflectance or light reflectance value of the surface.
In our lab, the luminance contrast between 2 surfaces is calculated according to AS 1428.1:2009 or AS/NZS 1428.4.1:2009, with the following equation:
Luminance contrast = 125 x (luminous reflectance 1 – luminous reflectance 2) / (luminous reflectance 1 + luminous reflectance 2 + 25)
For example, the luminous reflectance of surface 1 is 50% (luminous reflectance 1 = 50); the luminous reflectance of surface 2 is 25% (luminous reflectance 2 = 25); the luminance contrast between them can be calculated as:
Luminance contrast = 125 x (50 – 25) / (50 + 25 + 25) = 125 x 25 / 100 = 31.25
The luminance contrast is therefore 31.25 or 31.25%.
In the example above, the surface on the left (pale grey color) is significantly brighter than the surface on the right (deep grey color). The luminance contrast between them is large (69%).
In the example above, the surface on the right is only marginally brighter than the one on the left. The luminance contrast between them is small (only 0.7%). When such a surface pair is used as TGSIs, it will be very hard for people with vision impairment to identify them.
In the example above, the surface on the right (cyan color) is only slightly brighter than the one on the left (green color), the luminance contrast between them is small (only 1%), although they are quite distinct in color. Luminance contrast is different from color contrast. TGSIs with large color contrast but small luminance contrast are still not friendly to visually impaired people.