Intensity

• Intensity measures the amount of energy carried by a light wave or stream of photons.
• When light is modelled as a wave, intensity is proportional to the square of the amplitude.
• When light is modelled as a particle, intensity is proportional to the number of photons present at any given point in time.
• The intensity of light falls off as the inverse square of the distance from a point light source increases.
• Light intensity at any given distance from a light source is directly related to the power of the light source and the distance from the source.
• The power of a light source describes the rate at which energy is emitted and is measured in watts.
• The intensity of light is measured in watts per square meter (W/m²) and is also commonly expressed in lux (lx).

About intensity and brightness

Intensity

• Intensity refers to the amount of light energy passing through a unit area perpendicular to the direction of light propagation. It measures the concentration of light energy per unit area. Intensity is typically quantified in units such as watts per square meter (W/m²) or lux (lx). In the case of a point source of light, intensity decreases with distance according to the inverse square law.

Brightness

• Brightness, on the other hand, refers to the subjective perception of how intense or luminous a light source appears to an observer. It is the quality of being bright or emitting or reflecting a lot of light. Brightness is influenced by factors such as the intensity of the light source, the surface area over which the light is distributed, the spectral composition of the light, and the sensitivity of the human eye. Unlike intensity, which is a physical quantity measured objectively, brightness is a perceptual attribute and can vary from person to person.