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The candela (symbol: cd) is the unit of luminous intensity in the International System of Units (SI). [ 5][ 6] It measures luminous power per unit solid angle emitted by a light source in a particular direction.
Luminous intensity. In photometry, luminous intensity is a measure of the wavelength -weighted power emitted by a light source in a particular direction per unit solid angle, based on the luminosity function, a standardized model of the sensitivity of the human eye. The SI unit of luminous intensity is the candela (cd), an SI base unit .
Optical instrument. An illustration of some of the optical devices available for laboratory work in England in 1858. An optical instrument is a device that processes light waves (or photons ), either to enhance an image for viewing or to analyze and determine their characteristic properties. Common examples include periscopes, microscopes ...
t. e. In physics, Raman scattering or the Raman effect ( / ˈrɑːmən /) is the inelastic scattering of photons by matter, meaning that there is both an exchange of energy and a change in the light's direction. Typically this effect involves vibrational energy being gained by a molecule as incident photons from a visible laser are shifted to ...
Time. Watch, a time measurement device. In the past, a common time measuring instrument was the sundial. Today, the usual measuring instruments for time are clocks and watches. For highly accurate measurement of time an atomic clock is used. Stopwatches are also used to measure time in some sports.
Visibility. For other uses, see Visibility (disambiguation). In meteorology, visibility is the measure of the distance at which an object or light can be clearly discerned. It depends on the transparency of the surrounding air and as such, it is unchanging no matter the ambient light level or time of day.
A photometer is an instrument that measures the strength of electromagnetic radiation in the range from ultraviolet to infrared and including the visible spectrum. Most photometers convert light into an electric current using a photoresistor, photodiode, or photomultiplier . Photometers measure: Illuminance. Irradiance.
CGS. 1.076 × 10−3 phots. A foot-candle (sometimes foot candle; abbreviated fc, lm/ft2, or sometimes ft-c) is a non- SI unit of illuminance or light intensity. The foot-candle is defined as one lumen per square foot. This unit is commonly used in lighting layouts in parts of the world where United States customary units are used, mainly the ...