Light from a spark was used to produce a primary ionizing event in a Geiger counter by means of the photoelectric effect. The time lag between this event and the detection of the pulse on the counter wire was studied as a function of counter filling, pressure, and overvoltage. The measured lags, ranging from tenths of microseconds to many microseconds, were used to calculate electron mobilities, sheath spread velocities, and electron attachment coefficients. The lags appear to be the result of the transit time required by the initial electrons to move from their point of origin to the high field region, and the time required by the sheath to spread laterally along the wire and to move radially outward far enough to produce an electrical pulse which can be detected.