(a) Trace data of photon bursts detected using a confocal LIF setup for the fluorescent spheres. A threshold level of 3,000 cps was set to discriminate true single particle events from background fluorescence fluctuations. (b) Trace data of photon bursts detected using the compact SMD instrument for the fluorescent spheres. In this case, a threshold level of 40,000 cps was set to discriminate single particle events from background fluorescence fluctuations. (c) Histogram of photon burst intensities constructed from the data set in (a) using the confocal LIF setup. The accepted photon bursts were compiled into bins of 5,000 cps. (d) Histogram of photon burst intensities from data in (c) using the compact SMD instrument. The data in this case were accumulated into bins of 20,000 cps.