Measurement of the emission (350–750 nanometers) from single 5–50µ particles of various phosphor systems under 2537Aå excitation has been achieved utilizing a modified fiber optic microspectroradiometer. The system greatly facilitates identification of phosphor components in blends often employed in fluorescent lamps and has enabled positive identification of most phosphors from their respective emission spectra. Minor secondary phases present in experimental phosphors, which had heretofore been impossible to verify with standard spectroradiometric equipment, have now become readily identifiable. Successive stages of phosphor activation of the system , Mn+2 have been explored with variations in spectral characteristics of particles occurring not only in different locations of the firing vessel, but among adjacent grains within a small volume. Particles from standard cool white fluorescent lamps have been found to exhibit slight variations in Sb+3 to Mn+2 emission ratios resulting in possible luminous efficiency losses. Brightness profile data across individual cool white phosphor grains, utilizing a 1.2,µ measurement probe area have indicated variations of the order of 10–15% difference across single grains. Brightness data from particle to particle have also indicated substantial differences.