{"url":"https:\/\/siunits.stuchalk.domains.unf.edu\/api\/baseunit\/candela","pid":"si:unit:candela:2019","name":"candela","urlname":"candela","definition":"The candela, symbol *cd<\/em>, is the SI unit of luminous intensity in a given direction. It is defined by taking the fixed numerical value of the luminous efficacy of monochromatic radiation of frequency 540 × 10*^{12<\/sup> Hz<\/em>, K<\/em>cd<\/sub>, to be 683 when expressed in the unit lm W-1<\/sup>, which is equal to cd sr W-1<\/sup><\/em>, or cd sr kg-1<\/sup> m-2<\/sup> s3<\/sup><\/em>, where the kilogram, metre and second are defined in terms of h<\/em>, c<\/em> and Δν<\/em>Cs<\/sub>.","source":"SI Brochure 9th Ed. 2019, p 135","source_url":null,"siunit":null,"startdate":"2019-05-20","enddate":null,"status":"Valid","reference":"CGPM Resolution 1 of the 26th CGPM (2018) \"On the revision of the International System of Units (SI)<\/a>\"","reference_url":null,"year":2019,"names":"candela:candela","pinfo":null,"notes":{"1":"This definition implies the exact relation \\(K_{\\rm{cd}} = 683\\ {\\rm{cd\\:sr\\:kg^{-1}\\: m^{-2}\\:s^{3}}}\\) for monochromatic radiation of frequency \\(\\nu = 540 \\times 10^{12}\\ {\\rm{Hz}}\\). Inverting this relation gives an exact expression for the candela in terms of the defining constants \\(K_{\\rm{cd}}\\), \\(h\\) and \\(\\Delta\\nu_{\\rm{Cs}}\\):\n$$1\\ {\\rm{cd}} = \\left( \\frac{K_{\\rm{cd}}}{683} \\right)\\ {\\rm{kg\\:m^{2}\\:s^{-3}\\:sr^{-1}}}$$\nwhich is equal to\n$$1\\ {\\rm{cd}} = \\frac{1}{(6.626\\,070\\,15 \\times 10^{-34})(9\\,192\\,631\\,770)^{2}\\,683} (\\Delta\\nu_{\\rm{Cs}})^{2}\\,h\\:K_{\\rm{cd}}$$\n$$\\approx 2.614\\,830 \\times 10^{10} (\\Delta\\nu_{\\rm{Cs}})^{2}\\:h\\:K_{\\rm{cd}}$$","2":"The effect of this definition is that one candela is the luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency \\(540 \\times 10^{12}\\ {\\rm{Hz}}\\) and has a radiant intensity in that direction of \\((1\/683)\\ {\\rm{W\/sr}}.\\) The definition of the steradian is given below Table 4."},"related":[{"relationship":"hasUnitSymbol","weburl":"https:\/\/siunits.stuchalk.domains.unf.edu\/si\/definition\/unitsymbol\/cd","apurl":"https:\/\/siunits.stuchalk.domains.unf.edu\/api\/unitsymbol\/cd"},{"relationship":"hasDefiningEquation","weburl":"https:\/\/siunits.stuchalk.domains.unf.edu\/si\/definition\/definingequation\/candela_equation","apurl":"https:\/\/siunits.stuchalk.domains.unf.edu\/api\/definingequation\/candela_equation"}],"date":"2024-07-24T05:46:10+00:00"}}