If you have a
light source
that radiates uniformly in all directions (that part is important - a candle or a regular household incandescent bulb, for example), the light intensity will fall off as the "inverse square of the distance."
If the intensity of a typical candle is 1 lux measured at a distance of 1 meter away from the flame, its intensity at 2 meters will be 1/4 of a lux (1/22). At 3 meters, the intensity will be 1/32 or 1/9 of a lux. And so on.
