A Method for Measurement of the Spectral Characteristic of an Integrating Sphere

For accuratehotometrywith an integrating sphere, the spectral characteristic of the paint on the inner surface, or preferably of the whole integrator, must be examined spectrophotometrically. This report describes a method of measuring the spectral characteristic of a whole integ rator including a diffusing glass window or a concave mirror.Color temperature of luminous flux in directions of every 30° is studied on a standard lamp of luminous flux at 2788°K. The results show that the variation of the color temper ature with directions is so small that the relative spectral energy distribution of the total luminous flux emitted by the lamp is considered practically the same as that of the flux in a given direction.Then the lamp is operated in a sphere and the light from the sphere windo w (or from some part of the inner surface) is measured spectrophotometrically. Similarly, the reflected light from a plate smoked with MgO, which is Illuminated with the lamp, is measured. The ratios of these two sets of measured values at each wavelength give the required characteristic of the whole integrator, subject to the cor ection of the spectral reflectance of the MgO plate.