Lumen lm
About the Lumen
The lumen measures the total visible light emitted by a source, weighted for the sensitivity of the human eye. A source of one candela radiating equally in all directions emits 4π lumens. Lamp packaging lists lumens to compare brightness independently of power draw.
Related Units
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...
Candela
cdBase unit; Kcd = 683 lm/W at 540 × 10¹² Hz exactly
The candela is defined by fixing the luminous efficacy of monochromatic radiation of frequency 540 × 10¹² hertz, a...
Hertz
Hz1 Hz = 1 s⁻¹
The hertz is one cycle or event per second and replaced the older expression cycles per second. It is named after...
Radian
rad1 rad = 1 m/m (dimensionless); 180°/π
A radian is the angle subtended at the centre of a circle by an arc equal in length to the radius, so a full turn is 2π...