How is the intensity of light defined?

The intensity of light is defined as the power per unit area of light. This definition is rooted in how we measure the amount of energy carried by light waves as they pass through a specified area over a certain amount of time. Intensity quantifies how much power (energy per unit time) is being delivered over a given area.

In practical terms, if you think about how sunlight reaches the Earth, the intensity refers to how much of that sunlight energy is distributed across each square meter of surface area. This aspect of light is critical in several applications, including photography, solar energy systems, and understanding the effects of radiation on materials.

The other options relate to different properties of light but do not define intensity. The speed of light in a vacuum is a constant that describes how fast light travels, while the energy content of light refers to the total energy carried by photons, not specifically addressing the distribution of that energy over an area. The wavelength of light pertains to the distance between successive peaks of a light wave, influencing its color and other properties but is not related to intensity. Thus, the correct understanding of intensity being power per unit area is essential for comprehending various phenomena in optics and light behavior.