A device for measuring light scattering distribution, a goniophotometer, was improved with new detector geometry and faster data acquisition, and validations of the accuracy were made. The detector linearity was verified with a liquid variable absorber and angular positions using a diffraction grating. The angular-resolved scattering data were numerically integrated to be compared with integrating spheres. For this a new integration method uses Voronoi cells on a sphere to integrate arbitrarily located data points, using adaptively refined angular resolution of the measured scattering data. This links the bidirectional-reflection-transmission function (BRTF) of goniophotometers with the direct-hemispherical transmittance values typically given by integrating spheres.