I personally always imagine light rays being like water just without a gravitational pull towards the earth. This way, in my imagination water shooting out of a water hose would spread forever and ever in the direction I'm pointing my hose at.
Depending on which attachement you have on your water hose and how large the original opening of the hose is, more or less water comes out as well as a more or less focused jet. So, using a funnel shape for an opening, the water jet wouldn't only be linear but also spreat out to the left and right.
Depending on how close the object or person we want to photograph is to the light source aka. our water hose, the more water will get on them and the wetter they will be. But as soon as the person moves away form the light source, the amount of light that still reaches the person decreases steadily.
If you shine a flashlight on the person in front of you, almost certainly 100 % of the light beam will hit the person and illuminate them. However, if the person moves back only a couple of meters, the light beam widens and probably only about 30% of the light will actually still reach its target. The rest will be lost to the surroundings.
Basically we can conclude that not the distance is responsible for the person getting darker but the spread of the light that is lost to the surroundings. The narrower the beam, the less the light rays will stray and illuminate what you don't actually want to illuminate.
This would mean, that with a focused beam of light it wouldn't make any difference how far the person is standing away from you. The same amount of light would hit her at a 1 meter distance as it would if she were standing 10 meters away.
