Intensity and luminous intensity are two related but distinct concepts used in different contexts to describe different types of physical quantities.
- Intensity: In general physics, intensity refers to the amount of energy transferred or carried by a wave per unit of time and per unit of area perpendicular to the direction of wave propagation. It is a measure of the concentration or density of energy. Intensity can be applied to various types of waves, such as sound waves, electromagnetic waves (including light), and even waves in fluids.
For example, in the case of sound waves, intensity is the amount of sound energy passing through a given area per unit of time. It is often measured in units such as watts per square meter (W/m²) or decibels (dB).
- Luminous Intensity: Luminous intensity, on the other hand, is a specific term used in the context of light and vision. It refers to the amount of light energy emitted or transmitted in a particular direction per unit of solid angle. Luminous intensity is a measure of the perceived brightness or strength of light as perceived by the human eye.
Luminous intensity is measured in units called candelas (cd). One candela is defined as the luminous intensity in a given direction of a light source that emits monochromatic green light with a frequency of 540 terahertz and has a radiant intensity of 1/683 watt per steradian.
In summary, while intensity is a general term used to describe the concentration or density of energy in waves, luminous intensity specifically refers to the brightness or strength of light as perceived by humans and is measured in candelas.