Overview
Silicon photodiodes are semiconductor devices that generate current when exposed to light or particles. Photons with energy greater than 1.12 eV (wavelengths shorter than 1100 nm) excite electrons from the valence band to the conduction band, enabling current flow. This current is proportional to the incident energy.

The Inverse Square Law states that light intensity (I) decreases with the square of the distance (r) from a point source. The formula is:

As distance increases, intensity decreases. For example, doubling the distance reduces the intensity to one-quarter. This applies to any radiation spreading in all directions.

Significance
Fundamental to quantum mechanics, used in solar panels and sensors.