Integrating sphere measurements

A final geometry exists for directional illumination, diffuse collection integrating sphere measurements. The 30/T geometry (30° incidence, total hemispherical collection) is specified by the American Society for Testing and Materials (ASTM) for the measurement of acoustical ceiling tile reflectance, The author knows of no other applications that specify this integrating sphere geometry. 

Another problem arises in integrating sphere measurements when the sample cannot be placed flush against the port of the sphere, ff the sample is specular, the reference should be recessed by an identical distance as the sample to be measured. For materials that are primarily diffuse in character, we have determined the measured reflectance for a lambertian material decreases by approximately 3% (absolute) per millimeter of distance of the sample from the sphere up to approximately 4 mm. Beyond that, it is difficult to predict. Measurement of the reference at a similar distance helps but is still very inexact. 

Clarke, F. J. J., and Compton, J. A. Correction methods for integrating sphere measurements of hemispherical reflectance. Color Res. Appl. 11(4) (1986). 

The optoelectrical characteristics of the display have been measured using an integrating sphere and a calibrated photodetector connected to a radiometer [30]. First, the total luminous flux from the AM-PLED was measured for different /data. Then, the AM-PLED luminance was calculated from the measured display luminous flux. For a Lambertian emitter, the luminance (L) can be calculated from the measured luminous flux (<1>) by using the following equation ... 

Y. Hong and J. Kanicki, Integrating sphere CCD-based measurement method for organic light-emitting devices, Rev. Sci. Instrum., 74, 3572-3575, 2003. 

Figure 8.11. Diffuse reflectance absorption spectra of a strongly fluorescent sample (1,6-diphenylhexatriene adsorbed on porous alumina) (a) conventional measurement w ith monochromatic irradiation and detection via an integrating sphere (b) measurement in a fluorimeter with two monochromators. Reaction spectra during Irons - cis photoisomerization are also given (adapted from Ref. 26).

Hitzenberger, R., U. Dusek, and A. Berner, Black Carbon Measurements Using an Integrating Sphere, J. Geophys. Res., 101, 19601-19606 (1996). 

Fig. 7.4 Total transmission spectrum (measured with an integrating sphere) of a CD Agl fihn on glass.

When light is directed onto a sample it may either be transmitted or reflected. Hence, one can obtain the spectra by either transmission or reflection. Since some of the light is absorbed and the remainder is reflected, study of the diffuse reflected light can be used to measure the amount absorbed. However, the low efficiency of this diffuse reflectance process makes it extremely difficult to measure 120) and it was speculated that infrared diffuse reflection measurements would be futile 120). Initially, an integrating sphere was used to capture all of the reflected light121) but more recently improved diffuse reflectance cells have been designed which allow the measurement of diffuse reflectance spectra using FT-IR instrumentation 122). 

The energy of the laser pulse is measured using an integrating sphere and a (GeGaAs) photodiode, integrated by a boxcar. To ensure that mass spectra and laser energies are recorded in pairs, a home built amplitude to time converter is used to write the energy as a time delay at the end of each mass spectrum. 

UV-VIS-NIR diffuse reflectance (DR) spectra were measured using a Perkin-Elmer UV-VIS-NIR spectrometer Lambda 19 equipped with a diffuse reflectance attachment with an integrating sphere coated by BaS04. Spectra of sample in 5 mm thick silica cell were recorded in a differential mode with the parent zeolite treated at the same conditions as a reference. For details see Ref. [5], The absorption intensity was calculated from the Schuster-Kubelka-Munk equation F(R ,) = (l-R< )2/2Roo, where R is the diffuse reflectance from a semi-infinite layer and F(R00) is proportional to the absorption coefficient. 

All ground state diffuse reflectance spectra were recorded using a Phillips PU8800 UV-Visible spectrophotometer equipped with an integrating sphere, interfaced to an Elonex PC-386SX computer. These ground state diffuse reflectance spectra were measured relative to a BaSC>4 white reflectance standard (Eastman Kodak Ltd.). 

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