To our eyes a flash happens, well, in a flash! It appears instantaneous. But if you were to hook up an oscilloscope and the proper sensor you will see that a flash has a rise, a peak, and a fall. The rise is quite steep and the falloff starts almost immediately, but it then stretches out until the light totally fades. In most situations you don’t need to be concerned at all with the flash duration. It is almost always faster than your shutter speed in normal sync mode (we will talk about high speed sync separately).