The relationship between light-emission patterns from silicon avalanche-mode light-emitting diodes (AMLEDs), and avalanche breakdown was investigated using photodiodes fabricated in pure boron (PureB) technology. The quality of the diodes ranged from highquality, low dark-current devices with abrupt breakdown characteristics that were suitable for operation as singlephoton avalanche diodes (SPADs), to diodes with gradually increasing reverse currents before actual breakdown. The reverse I-V characteristics were measured and correlated to light-emission data obtained simultaneously using a PureB photodetector, and inspected using a camera with which distinct emission patterns could be identified. When increasing the voltage far past breakdown, light emission invariably becomes dominant at the photodiode periphery. Based on the examination of a large variety of anode geometries, it is concluded that the most efficient light emission per consumed power is achieved with defect-free narrow-anode diodes that also are applicable as low-darkcount-rate SPADs.