Which is most important in the use of a camera photofl ash unit, the intensity of the light (the energy per unit area per unit time) or the product of the intensity and the time of the fl ash, assuming the time is less than the shutter speed

intensity of the light (the energy per unit area per unit time)

Explanation:

The photoflash capacitor is an electrolytic capacitor that is also used in flash cameras, professional illumination and solid-state laser supply. Their general purpose is to briefly power a high-voltage flash tube, which can be used to illuminate photographic material or to alternately pump a laser rod. Since the flash tube requires very little time to operate, photoflash capacitors are designed to supply high discharge current pulses without excessive internal heating.