Expert in Optical & Thermal Measurement Solutions
We are able to test the daylight reflectance of full-size solar panels. Shown below is an example.
All typical commercial solar panels can be tested, including panels greater than 1.2 m x 2.4 m in size. The results reported are the same as our standard daylight reflectance testing service (sample report). Due to the extra effort in handling such large and heavy samples, some large-size sample surcharge is applicable.
In the daylight reflectance test, the specular daylight reflectance is calculated as:
Specular daylight reflectance = Total daylight reflectance – Diffuse daylight reflectance
Due to the rounding operations, the reported specular specular daylight reflectance could be:
Specular daylight reflectance = Total daylight reflectance – Diffuse daylight reflectance ± 0.001
Shown below is an example result set, with this ± 0.001 discrepancy:
Some customers expect that the specular daylight reflectance should be 0.216 – 0.200 = 0.016 (1.6%) and suspect that there is a typo in the test report.
Our daylight reflectance test reports are generated by in-house software automatically. The ±0.001 discrepancy is not due to a calculation mistake or a typo, but due to the rounding operations, as illustrated in the table below:
| Before rounding | After rounding | |
|---|---|---|
| Total daylight reflectance | 0.2156 | 0.216 (21.6%) |
| Diffuse daylight reflectance | 0.2004 | 0.200 (20.0%) |
| Specular daylight reflectance | 0.0152 | 0.015 (1.5%) |
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:
Please refer to our daylight reflectance page for more information.
According to BCA’s requirements on daylight reflectance, there are different requirements for the following installation locations:
We were asked by many customers if we test the daylight reflectance at different inclination angles, in order to meet BCA’s requirements.
The short answer is: no, we do not test the daylight reflectance at different inclination angles.
Daylight reflectance, as a material property, is independent of its inclination angle. The angle in BCA’s requirement is the installation angle, it does not mean that daylight reflectance needs to be tested at various inclination angles.
Daylight reflectance is a material property and it does not change with its inclination angle.
For example, for a surface with 10% of total daylight reflectance, its total daylight reflectance remains 10%, when the surface is tilted.
The test angle in the laboratory is dependent on the test instrument design and it is different from the installation angle in a building project.
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.
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:
They are the same in physical meaning: all of them are quantities representing the fraction of visible light reflected by a surface.
For general applications, the results are equivalent. For example: 0.50 (50%) of daylight reflectance = 0.50 (50%) of visible light reflectance = 0.50 (50%) of luminous reflectance = 50 of light reflectance value (LRV).
In practice, there are some subtle differences in the test results, due to the different test methods used. Below are the practices implemented in our lab:
Most of the time, the results obtained with different methods are very close (typically less than ±0.01 of variation).
Both quantities are about the reflectance of material surfaces. However, they are different.
Shown below is the solar radiation spectrum (red color part is for the sunlight at sea level). The solar radiation consists of 3 parts: 1) ultraviolet (UV) radiation; 2) visible light and 3) infrared (IR) radiation.
Additionally, in the lab, the daylight reflectance test and solar reflectance test are two different tests:
We are pleased to release our 2020 edition of laboratory profile, which is a 56-page comprehensive document, with rich information on our capabilities and many technical insights.
What are in the laboratory profile?
You may download a soft copy of our lab profile.
Can my material meet the BCA daylight reflectance requirements? Refer to the flow chart below for some graphical explanation of the rules.
