lichtkracht

Lichtkracht is a Dutch term that can denote either the power of light in a physical sense or more loosely the perceived strength or brightness of light. In precise Dutch science language, the term is not a standard SI quantity. The formal concepts typically used are radiant power (P, measured in watts), irradiance (E, W/m²), and, for human perception, luminous flux (Φv, lumens) and luminous intensity (Iv, candelas). Illuminance (lux) describes how much luminous flux reaches a surface.

Radiant power describes the total amount of electromagnetic energy emitted, transmitted, or received per unit time, across all wavelengths. Luminous flux weights this energy by the photopic luminous efficiency function to reflect perceived brightness and is measured in lumens. Luminous intensity describes the brightness perceived in a given direction and is measured in candelas. Illuminance, measured in lux, indicates how much luminous flux arrives on a surface per unit area.

In practical terms, lichtkracht may appear in Dutch discussions of lighting to convey one or more of these ideas: how bright a light source is, how much energy it emits, or how much of that energy is useful for human vision. The measurement depends on geometry and spectral content. For LEDs, lamps, or sunlight, engineers use P, Φv, Iv, and irradiance to quantify performance and safety.

Other related terms include radiance (radiant power per unit area per unit solid angle) and spectral power distribution, which describes how power is distributed across wavelengths.

Originating from the Dutch words licht (light) and kracht (power/strength), lichtkracht is widely used in Dutch-language popular science but is not a formal SI quantity.