The strength of light falling on an area is called irradiance.

Here's a breakdown:

* Irradiance is the power per unit area of electromagnetic radiation (including light).

* It's measured in units of watts per square meter (W/m²).

* The higher the irradiance, the stronger the light.

Other related terms:

* Illuminance: This is a measure of the light falling on a surface that is weighted to account for the sensitivity of the human eye. It's measured in units of lux (lx).

* Radiant flux: This is the total power emitted by a light source, measured in watts (W).

Let me know if you have any other questions!