Glossary of the most important Lighting Term



   As with any technical or scientific discipline, light technology has its own terminology.Special term and concepts are used to define the characteristics of lamps and luminaries and to standardize the units of measurement.



Light is taken to mean the electromagnetic radiation that the human eye perceives as brightness, in other words that part of the spectrum that can be seen. This is the radiation between 380nm and 760nm,a tiny fraction of the spectrum of electromagnetic radiation



Unit of measurement: lumen [lm]
     All the radiated power emitted by a light source and perceived by the eye is called luminous flux F




Unit of measurement: candela [cd]
     Generally speaking, a light source emits its luminous flux F in different direction and different and at different intensities.The visible radiant intensity in particular direction is called luminous intensity I




Unit of measurement: lux [lx]
     Illuminance E is the ratio between the luminous flux and the area to be illuminated.An illuminance of 1 lx occurs when a luminous flux of 1 lm is evenly distributed over an area of 1 square meter




Unit of measurement: candelas per square meter
     The luminance L of a light source or an illuminated area is a measure of how great an impression of brightness is created in the brain




Unit of measurement: lumens per watt [lm/W]
     Luminous efficacy Indicates the efficiency with which the electrical power consumed is converted into light




Unit of measurement: Kelvin [K]
     The color temperature of light source is defined in comparison with a "black body radiator" and plotted on what is knows as the "Plankian curve" the higher the temperature of this "black body radiator" the greater the blue component in the spectrum and smaller the red component.An incandescent lamp with a warm white lights, for example. Has a color temperature of 2700K, whereas a daylight fluorescent lamp has a color temperature of 6000K




      The light color of a lamp can be neatly defined in term of color temperature. There are three main categories hereWarm < 3300K Intermediate 330 to 500kDaylight > 5000KDespite having the same light color, lamps may have very different color rendering properties owing to the spectral composition of their light. 





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