Contoured housing features recessed controls to prevent accidental flashing. New modeling lamp circuit eliminates the timer control knob. Push the button to start or stop. The lamp automatically switches off after 20 seconds or after each flash, whichever comes first. The bright 50w quartz modeling lamp enables you to focus the camera in dimly lit areas and to preview the flash to prevent glare in eye glasses. Produces 50% more flash output than others we have tested becuase the modeling lamp is located in the reflector as opposed to inside the flashtube.