Candela cd
About the Candela
The candela is defined by fixing the luminous efficacy of monochromatic radiation of frequency 540 × 10¹² hertz, a green light near the peak sensitivity of the human eye, at exactly 683 lumens per watt. It replaced older standards based on candles and glowing platinum. An ordinary wax candle emits roughly one candela, which is where the name comes from.
Related Units
Lumen
lm1 lm = 1 cd·sr
The lumen measures the total visible light emitted by a source, weighted for the sensitivity of the human eye. A source...
Lux
lx1 lx = 1 lm/m²
One lux is one lumen spread over one square metre. Office lighting is typically a few hundred lux, while direct summer...
Metre
mBase unit; c = 299,792,458 m/s exactly
The metre is the length of the path travelled by light in vacuum in 1/299,792,458 of a second. It was first defined by...
Kilogram
kgBase unit; h = 6.62607015 × 10⁻³⁴ J·s exactly
The kilogram is defined by fixing the Planck constant at exactly 6.62607015 × 10⁻³⁴ joule-seconds. Until 20 May 2019 it...