What is the inverse square law of photography?

Refers to the intensity of an object or celestial body, which decays with the square of the distance. For example, the gravity generated by celestial bodies or the illumination of a light bulb decreases with the square of the distance.

The connection between it and the light in photography is not clear, I am an amateur

Aperture series and distance

Many photographers have found that the inverse square law is and Some very important numbers are closely related to the aperture number. This relationship is important since aperture stops are usually what you need to remember. Please consider the following facts: Experiments have found that a subject located 4 feet away from the light source receives 100 photometric units; at a distance of 5.6 feet, the received light is 50 photometric units; and if it is 8 feet away, the light received is 50 photometric units. The amount of light received is only 25 photometric units. Isn't this a bit familiar? These numbers for aperture stops, when converted to distance, give you insight into the secret of the inverse square ratio. You can convert aperture-stop numbers into any distance measurement unit and determine the luminosity at those distances.

Please consider the following instructions. If a light produces 100 photometric units at 4 feet, the drop rate at different "aperture level" distances is: 4 feet equals 100 photometric units, 5.6 feet equals 50 photometric units, and 8 feet equals 25 photometric units Photometric units, 11 feet equals 12.5 photometric units, and 16 feet equals 6.25 photometric units. Now test your understanding of this principle - what is the photometric unit of the above light at 2 feet? What's that at 22 feet?

You can measure the inverse drop effect of a light in feet, meters, inches, or any other unit of distance.