Luminous flux, or simply brightness, is measured with the unit lumen (lm) and denotes the physical quantity of the light power emitted by a light source in all directions.
In general, the higher the luminous flux, the brighter the light.
Watts are also often used as an indicator of brightness, but since different light sources have different efficiencies, wattage cannot be used to make an accurate statement about light intensity. For example, an ordinary 100W incandescent bulb has about 1000 lumens, while a 10W LED produces about the same light output.
Info: For the evaluation of illuminants, other light values, such as illuminance, beam angle, color temperature and color rendering index must be taken into account.