Illuminance (at a point of a surface): Quotient of the luminous flux incident on an element of the surface containing the point, by the area of that element. ![]() Quantity of light : Time integral of the luminous flux over a given duration. Ohno (1997) presented explicit and detailed descriptions of the relation between radiometric and photometric quantities. The luminous flux is calculated by integrating, from 0 nm to infinity (actually 360–830 nm for photopic vision), the product of spectral radiant flux, the CIE standard spectral luminous efficiency function for photopic vision (usually denoted as V( λ), with value ranges of 0–1 according to wavelength λ), and the maximum spectral luminous efficacy (of radiation) for photopic vision (usually denoted as K m approximately 683 lm W −1 at 555 nm (540 THz)). Luminous flux : Quantity derived from radiant flux by evaluating the radiation according to its action upon the International Commission on Illumination (CIE) standard photometric observer. The luminous flux must be compared for that purpose. A common error is comparison of the luminous output capability of the light source, especially LEDs, with the luminous intensity. In other words, it is the luminous flux leaving the source per unit of solid angle in the considered direction. Luminous intensity (of a source, in a given direction): Quotient of the luminous flux leaving the source and propagated in the element of solid angle containing the given direction, by the element of solid angle. Kazuhiro Fujiwara, in Plant Factory Basics, Applications and Advances, 2022 5.3.2.2 Fundamental photometric quantities The more frequent that cleaning and repainting of room surfaces occurs, the higher the RSMF ( Knisley, 2004). Periodical cleaning or repainting of the room surfaces (small rooms every year and larger rooms every two to three years) will lessen the overall impact of room surface dirt depreciation, which will be expressed by an improvement in RSMF. In (very) clean rooms the RSMF will be higher, while in (very) dirty rooms the RSMF will be lower. The ‘Lighting Handbook’ of IESNA has published lists of various RSMF values for direct, semi-direct, direct-indirect and indirect armature types and for five categories of cleanliness (very clean, VC clean, C medium, M dirty, D and very dirty, VD) and three cleaning intervals (cleaning every year, every two years or every three years). Further influencing factors are the size of the room and the type of lighting (direct to indirect emission) ( ERCO, 2010). The RSMF depends on the degree of soiling of the room or the ambient conditions of a room and the specified cleaning frequency. It signifies the ratio of the room surface reflectances before and after cleaning. RSMF takes into account the reduction of luminous flux due to the soiling of the room surfaces. Moerman, in Hygienic Design of Food Factories, 2011 Room surface MF In the normal case about 60-70% of luminous flux will reach the work plane (light output ratio).F. There are losses in the luminaire (absorption, transmission, reflection losses) and at the room perimeters (reflectance). Not all the luminous flux emitted by the lamp reaches the work plane. The ratio between luminous flux and the power consumed is known as Luminous Efficacy. ![]() The precise values depend on the brand involved, although the figures are always very similar. Luminous flux for a selection of artificial light sources:ġ00W high-pressure sodium lamp (color corrected) Luminous flux is measured in lumens (lm). All other photometric parameters are derivatives of luminous flux. Luminous flux is measured either for the interior as a whole or for a part of the interior (partial luminous flux for a solid angle). the volume of light emitted from a light source. Luminous flux is a photometric measure of radiant flux, i.e.
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