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| 150 mm Integrating Sphere |
Integrating spheres, in combination with UV/Vis and UV/Vis/NIR spectrophotometers, are extremely versatile accessories for high precision reflectance and scattered transmittance measurements on virtually any solid or liquid. Application areas range from surface characterization of solids to the photometric analysis of turbid, colloidal, transparent and translucent samples. Typical uses encompass quality assurance testing and product development measurements on textiles, dyes, paper and glass. Integrating spheres are the most commonly used accessories on UV/Vis/NIR spectrophotometers.
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| Light Paths in a Typical Integrating Sphere |
The PerkinElmer 150 mm integrating sphere optical design is shown above. The transmittance sample holder at the entrance of the sphere enables the measurement of light scattering solutions or solids more efficiently than in a standard focusing UV/Vis spectrometer with a conventional detector arrangement. In the latter configuration, sample transmitted light will be lost before it reaches the detector, resulting in significant photometric errors and uncontrolled variation between samples. The integrating sphere, however, collects all the light which has passed through the sample.
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| Total Reflectance and Diffuse Only Reflectance Modes |
For reflectance measurements,samples are mounted in the rear diffuse reflectance sample mount. Either total reflectance or diffuse reflectance only can be measured by placing either a light trap or Spectralon plate at the specular reflectance angle. Measurement on irregularly-shaped solids such as solar cells, textiles, prisms and lenses is also possible using the center-mount option in which the sample is suspended in the middle of the sphere. The transmittance and reference ports are also shown. The reflectance port islocated under the light blue coveron the right-hand side of theaccessory. Even very large samples,for example sheets of glass, can bebrought up to the reflectance port for analysis. Additionally, for small samples or to sample small areas on larger samples, a small spot kit is available to focusthe beam at the entrance, reflectance or center-ports of the sphere.
Common Applications
The characterization of solar cells - UV/Vis spectroscopy is a convenient method of characterizing the transmission loss of silicon photocells. Since the samples are highly scattering, an integrating sphere must be used. Using the center-mount facility, the reflectance of the solar cell can be measured at various angles to mimic the passage of the sun across the sky. The thickness of any coating over the silicon cell can be calculated if necessary.
The analysis of security ink
Color analysis - For highly accurate color measurements, ASTM recommends the use of a 150 mm integrating sphere. This yields absolute color values enabling accurate color matching and inter-lab transfer of color values. Smaller integrating spheres, such as the 60 mm sphere, are also used for the measurement of relative color measurements, for example when the color of a product is verified over time against an internal standard. The spectra are traceable to international standards such as CIE, ASTM, ANSI, DIN and EN.
Distinction between specular and diffuse reflectance - Samples with different gloss characteristics or varying surface polishing can be analyzed in specular and diffuse reflectance mode. A standard gloss trap in the 150 mm integrating spheres allows the measurement of the diffuse component only.
Concentration determination of dyes in textiles - In diffuse reflectance measure- ments, the Kubelka-Munk function provides equivalence to absorbance in transmission spectroscopy. It is proportional to concentration and thus can be used for quantitative analysis of chemical compoundsin solids. little or no sample preparation is required. An integrating sphere system provides excellent qualitative as well as quantitative answers. After calibration the content of fat, protein and water can be obtained in a single measurement.
SPF value for sunscreens and cosmetics
Particle sizing
