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.
20% total daylight reflectance
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.
Total daylight reflectance
RGB (123, 123, 123) Hex (#7B7B7B)
RGB (248, 0, 0) Hex (#F80000)
RGB (0, 144, 0) Hex (#009000)
RGB (0, 0, 255) Hex (#0000FF)
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:
Indoor side (4 quantities): daylight illuminance [lux], solar irradiance [W/m2], air temperature [°C] and glass surface temperature [°C]
Outdoor side (3 quantities): daylight illuminance [lux], solar irradiance [W/m2], air temperature [°C]
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.
Primary solar heat gain: the solar heat directly transmitted through a glass in its original solar radiation form.
Secondary solar heat gain: the solar heat absorbed by a glass and further transferred to the indoor space as heat and via all 3 heat transfer modes (conduction, connection and radiation)
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:
Its primary solar heat gain is 30%: 30% of the overall solar energy is directly transmitted to the indoor space
Its secondary solar heat gain is 20% × 0.25 = 5%: 20% of the overall solar energy is absorbed by the glass and 0.25 fraction of it is transmitted to the indoor space;
Its SHGC is therefore 30% + 5% = 35% or 0.35.
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.
Partially fritted glasses: glass or non-glass material?
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:
With specular reflectance only
With mixed reflection
With diffuse reflection only
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.
Specular reflection only
With specular reflection only
Diffuse reflection is negligible
For such materials:
Diffuse reflectance = 0%
Total reflectance = specular reflectance
Materials with mirror finish
Metallic coating on glasses
With both specular reflection and diffuse reflection
Both components are not negligible
For such materials:
Total reflectance = diffuse reflectance + specular reflectance
Most general facade and roof materials with certain glossiness
Glasses with ceramic frit
Diffuse reflection only
With diffuse reflection only
Specular reflection is negligible
For such materials:
Specular reflectance = 0%
Total reflectance = diffuse reflectance
Materials with matt and rough surfaces: e.g. roof tiles, rough granites
The information presented above is our opinion. It is not reviewed, agreed, or approved by any external parties.
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:
The luminance contrast is therefore 31.25 or 31.25%.
A few examples of luminance contrast
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.