Abstract: A particle characterization system including a flow source to produce a stream of particles; a source of light or other energy directed at the stream of particles to cause fluorescence or scattered light to be emitted from the particles; a detector of the fluorescent or scattered light including a plurality of light receivers in an enclosed three-dimensional arrangement to detect the light emitted by the particles; and a computer which receives information from the detector regarding light emitted by a particle in response to the source of light or other energy, the computer programmed to determine a characteristic of the particle based on the light collected from the particle.