Valgustustihedus

Valgustustihedus, often translated as luminous intensity, is a fundamental photometric measure describing the power of light emitted by a source in a particular direction. It quantifies how bright a light source appears to the human eye when viewed from a specific angle. The standard 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 × 10^12 hertz and that has a radiant intensity in that direction of 1/683 watt per steradian.

Luminous intensity is distinct from luminous flux, which measures the total amount of visible light emitted by a source in all directions. While luminous flux is measured in lumens, luminous intensity takes into account the directional aspect of light. This means that a light source might have a high luminous intensity in one direction and a low intensity in another, even if its total luminous flux is the same.

The concept of luminous intensity is crucial in various applications, including lighting design, photography, and the calibration of light-measuring instruments. For instance, when specifying a spotlight, its luminous intensity in the direction of the beam is a key parameter. Understanding valgustustihedus helps in predicting how well a light source will illuminate a target area and how bright it will appear to an observer. It is a measure that directly relates to our perception of brightness.