![]() ![]() This concept can also be transferred to plants. The determination of illuminance is therefore described by the following equation: The factor K m is from the physical definition of the SI base unit for light intensity, 683 lm/W. The value obtained is then multiplied with the proportionality factor Km in order to calculate the photometric quantity illuminance E v. For low level lighting conditions an additional sensitivity curve is defined for the human eye, the so called scotopic spectral sensitivity.įigure 1: Spectral function of the eye for photopic and scotopic visionįor example, to determine the intensity of visible light on a surface, the measured physical (radiometric) quantity spectral irradiance E e is weighted by the V(λ) curve and integrated over the defined spectral range. This spectral responsivity weighting function, commonly referred to as the photometric or V(λ)curve, is used to derive photometric parameters such as the illuminance in lux or luminous flux in lumens from absolute radiometric measurements. First published by the CIE, the V(λ) curve describes the average spectral sensitivity of human visual perception of brightness under normal (photopic) lighting conditions such as daylight. ![]() The human eye but does not have an equal sensitivity to all wavelengths in the visible spectrum of light. They offer particular advantages when assessing LED grow lights, for example, compared to traditional PAR sensors. The spectral light meter products that are described in this paper have been developed by Gigahertz-Optik GmbH with functions specifically developed for this application. ![]() It describes the basics of light measurement with respect to the absorption of light by plants and its effect on plant growth, etc. This technical article presents the theoretical fundamentals and metrological implementation of photosynthetically active radiation (PAR) measurements. ![]()
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