Male fireflies produce species-specific bioluminescent courtship flashes consisting of single or multiple flash pulses. Females respond to these flashes with bioluminescent flashes of their own, and multiple males may simultaneously court a single female providing the opportunity for both male competition and female choice. Previous studies in Photinus fireflies have demonstrated intra-specific variation in male flash pulse duration, inter-pulse interval, pulse rate, duty cycle and number of pulses within the flash pattern as well as female preference as a function of flash rate, flash duration and flash intensity. However, little is known about varition in the flash envelope, the rate at which flash intensity rises and decays during flashes, or how courtship interactions with potential mates and competitors may influence male flash characters. In this study we measured male flash signals in terms of both the duration and shape of the flash envelope for P. ignitus and P. pyralis. We found intra-individual and intra-specific variation in these flash characteristics. Using these results we have developed microcomputer-based instruments that can perform real-time analysis of flash signals and produce appropriate simulated flash behaviors, providing for realistic measurement of male flash activity in the context of competition and courtship. We discuss the implications of this research for understanding the potential for male flash signals to serve as honest indicators of male quality.