1983 Volume 67 Issue 2 Pages 80-86
Two methods were proposed to determine accurately the relative spectral integrating sphere efficiency which plays an important role in the colorimetry for fluorescent materials by means of conventional color-measuring spectrophotometers.
The first method measures directly the relative spectral sphere efficiency by use of the irradiating light so urce and the reference white diffuser with the arrangement where either the fluorescent material or the standard white diffuser is placed alternately at the sample port of the integrating sphere. In this method the relative spectral sphere efficiency can be determined without using the spectral characteristics of the light source and the reference white diffuser.
The second method is an indirect estimation method which gives the efficiency by the calculation on the basis of the two quantites; the estimated value of the sphere wall reflectance based on the measurements where a light trap or a white diffuser is placed at a sphere port, and the ratio of the spectral sphere wall radiances when the standard white diffuser or the fluorescent material is placed alternately at the sample port. The accuracy of the second method was confirmed by comparing the values obtained from the method with the values directly measured by the first method. As a result, the color difference was less than 1.6 CIE LUV unit for several fluorescent materials.
Further, a simplified calculation method of the integrating sphere efficiency tried first by Billmeyer, Jr. et al. was also compared. As a result, this simplification method can include the error caused by neglecting the effect of the re-absorption and the re-emission of the fluorescence in addition to the error caused by the assumption of ideal integrating sphere. The errors of the colorimetric quantities are estimated to be more than 2.0 CIE LUV units for several fluorescent materials.