Lichtstärke

Lichtstärke, often translated as luminous intensity, is a fundamental photometric measure of the perceived power of light, as evaluated by the human eye. It quantifies the amount of visible light emitted by a point source in a particular direction per unit solid angle. The SI unit for luminous intensity is the candela (cd). One candela is defined as one lumen per steradian (lm/sr).

The concept of luminous intensity is crucial in understanding how brightly a light source appears to us. It takes into account the sensitivity of the human eye, which is not uniform across all wavelengths of visible light. The eye is most sensitive to light in the green-yellow region of the spectrum (around 555 nanometers). Therefore, a light source emitting strongly in this range will have a higher luminous intensity than a source emitting the same amount of radiant power at other wavelengths.

Luminous intensity is distinct from other photometric quantities like luminous flux (measured in lumens), which represents the total amount of visible light emitted by a source in all directions, and illuminance (measured in lux), which describes the amount of light falling on a surface. Luminous intensity is a directional quantity, meaning it can vary depending on the angle from which the light source is viewed. This makes it particularly important for applications such as designing lighting for specific areas, specifying the brightness of LEDs, and understanding the performance of lamps.