Measuring diffuse reflectance of solid samples from 360 to 2500nm
The ARCspectro VIS-NIR DR combines two spectrometers: a standard multichannel grating spectrometer that covers the visible spectral range (360nm-950nm) and the Arcoptix NIR scanning Fourier-transform spectrometer with an extended range InGaAs detector which is sensitive in the NIR range from 900 to 2500 nm. Both spectrometers are connected to a 5 cm integrating sphere. The sample is illuminated with perfectly diffuse light thanks to the integrating sphere including a high power halogen lamp.
The ARCspectro VIS-NIR DR allows you to measure the reflectivity of materials and paints over the complete solar spectral range – from 360 to 2500nm. This is important for the painting, building or solar energy industries, because it provides crucial information about the solar energy absorbed and transformed into heat by those materials or paints.
Those charateristics make it an ideal tool for measuring the Total Solar Reflectance (TSR) according to the ASTM ® norms G173 and E903. The software included with the VIS-NIR DR automatically calculates the TSR value. The ArcSpectro VIS-NIR DR complete measurement system is proposed for only 24’900 EUR. This offers an interesting alternative to other commercially available spectrophotometers which may be more versatile but are also slower, more complex, and much more costly.
The ARCspectro VIS-NIR DR combines a multichannel grating spectrometer, covering 360nm-950nm, with a scanning Fourier-transform spectrometer with an extended range InGaAs detector, which is sensitive in the NIR range from 900 to 2500 nm. Both spectrometers are connected to the internally illuminated integrating sphere via a bifurcated optical fiber.
The use of an Fourier transform spectrometer for the NIR and a grating spectrometer for the VIS is the optimal solution for diffuse reflection measurements:
For the VIS range it is preferable to have high sentivity because of the decreasing intensity of the halogen lamp in particualr for wavelengths below 450nm. So a grating spectrometer is the most adequate choice for this spectral range.
For the NIR spectral range, the Fourier-transform scanning spectrometer is superior to gratings spectrometer. Indeed, multichannel grating spectrometers are based on diode arrays with defective pixels and other problems. These problems are particulary important in the long range NIR (up to 2.5 microns) where InGaAs arrays suffer from severe technical limitations.
Total solar reflectance (TSR)
Lowering our need for energy and reducing our carbon footprint are crucial objectives for our future. Houses must be as energetically autonomouns as possible, which has to be achieved with a well engineered energy balance, and good thermal insulation. Solar radiation participates to this energy balance. In some situations, such as in cold countries, one may want the solar radiation to be absorbed as much as possible to help heating the building. In warm countries, converesely, a highly reflective surface is preferable.
However, is the a reflectivity measurement in the visible range of the solar spectrum sufficient to asses the overall reflectivity of a surface?
As illustrated in the graph below, more than half of the enegy of the solar spectrum lies in the near-infrared (NIR) between 700 and 2500nm. This radiation participates to the heating, and must therefore be taken into account.
In order to give a standard comparison between the reflectivity of different surfaces, that takes into account the whole solar spectrum, a standard parameter called Total Solar Reflectance (TSR) has been introduced. Essentially, the TSR is a reflectivity ponderated by a standardized solar spectrum (see ASTM ® norms G173 and E903):
The following figure illustrates the VIS-NIR reflectivity spectrum of two different paints. Their reflectivity of both paints is the same in the visible range, but it is considerably different in the NIR range. Hence, although these two paints would look identical to the human eye, one of them will absorb more solar radiation than the other.
The ARCspectro VIS-NIR was expressely developed to measure the TSR. It does cover the whole spectral range from 360 to 2500nm, and it is a fast, reliable, easy to use and comparatively low-priced instrument.
The ARCspectro VIS-NIR comes with a free, Windows 7 & Windows 10 compatible program. The spectrometer is connected to a computer via the USB port and automatically recognized.
The Software is a very easy to use application that permits to extract and to save spectral results such as colorimetric and TSR values from the measured sample after only 5 seconds measurement.
The Total Solar Reflectance (TSR) is calculated according to the ASTM ® norms G173 and E903.