THE CANDELA
 

The candela, symbolized by the lowercase nonitalicized pair of English letters cd, is the unit of luminous intensity. It is equivalent to 1/683 of a watt of radiant energy emitted at a frequency of 5.4 × 10¹⁴ hertz (cycles per second) in a solid angle of one steradian. (The steradian will be defined shortly.) This is a sentence full of arcane terms! However, there is a simpler, albeit crude, definition: 1 cd is roughly the amount of light emitted by an ordinary candle.
Another definition, more precise than the candle reference, does not rely on the use of derived units, a practice to which purists legitimately can object. According to this definition, 1 cd represents the radiation from a surface area of 1.667 × 10^-6 square meter of a perfectly radiating object called a blackbody at the solidification temperature of pure platinum.

مواضيع ذات صلة

THE TESLA

THE WEBER

THE HENRY

THE FARAD

THE HERTZ

THE SIEMENS

THE OHM

THE VOLT

THE COULOMB

THE WATT

THE JOULE

THE NEWTON