Light from a point source, such as a candle, radiates outward uniformly in all directions. As the distance from the point source increases, the energy from the source is spread ever more thinly.

For a projector, even though the light energy is being focused towards a screen, the Inverse Square Law still applies.

If you calculate the image area and intensity represented in the projector graphic, your results will match the Inverse Square Law: Area of a Projected Image table.
If the distance from image "A" is doubled from 20 feet (6.1 m) to 40 feet (12.2 m), then the total area becomes four times as large.
Inverse Square Law: Area of a Projected Image
In the table, the total area is four times larger at a distance of 40 feet (12.2 m), and the energy is one-fourth as intense.
DistanceEnergy IntensityArea in sq. ft (m2)

20 feet (6.1 m)

100%

36 (3.34 m2 )

40 feet (12.2 m)

25%

144 (13.38 m2 )

60 feet (18.3 m)

11%

324 (30.1 m2)

80 feet (24.4 m)

6%

576 (53.51 m2)