Valgustugevus

Valgustugevus is an Estonian term that translates to luminous intensity in English. It is a fundamental photometric measure that quantifies the power of light emitted by a source in a particular direction, weighted by the sensitivity of the human eye. This means it doesn't just measure the raw power of the light, but how bright that light appears to us.

The SI unit for luminous intensity is the candela (cd). One candela is defined as the luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 540 x 10^12 hertz and that has a radiant intensity in that direction of 1/683 watt per steradian. This definition ensures a consistent and reproducible standard for measuring light.

Valgustugevus is distinct from luminous flux, which measures the total amount of visible light emitted by a source in all directions, and illuminance, which measures the amount of light falling on a surface. Instead, valgustugevus focuses on the light emitted from a specific point in a specific direction, making it crucial for understanding the directional properties of light sources. It is commonly used in applications like lighting design, where understanding how much light is directed where is important, and in the characterization of lamps and LEDs.