the intensity of light on the subject can also be changed
by moving the flash head or light closer to increase the intensity
or further away to reduce it.
If the unit is moved twice the distance away from the subject,
the amount o flight reaching the subject is not 1/2, but 1/4
or two stops. This is why it is impossible to use an on camera
flash to illuminate a sports event like the olympics from
the stand, the distance is too great and by the time the light
has reached the athlete the power has diminished to the point
where there is little effect.