Definition of Light Intensity
Light intensity is a quantitative measure of the amount of light energy or power that falls on or is emitted from a surface per unit area. It describes the strength or brightness of light at a particular point, indicating how concentrated the light energy is.
How Light Intensity is Measured
The measurement of light intensity depends on whether one is considering the physical radiant power or the perceived brightness. Physically, radiant intensity is measured in watts per steradian (W/sr) or, more commonly, illuminance in lux (lumens per square meter, lm/m²) for the light that hits a surface, or luminance in candelas per square meter (cd/m²) for light emitted by a surface.
Factors Affecting Light Intensity
Several factors influence light intensity. The primary factors include the power of the light source itself and the distance from the source; intensity typically decreases with the square of the distance from a point source, known as the inverse-square law. Other factors like absorption, reflection, and scattering by intervening media also reduce perceived intensity.
Importance and Applications
Understanding light intensity is fundamental across many scientific and practical applications. It is crucial in astronomy for characterizing stars and galaxies, in photography for achieving proper exposure, in environmental science for studying plant growth and solar radiation, and in lighting design to ensure adequate illumination for various tasks.