An important specification for a light source is the luminous flux in the unit lumen [lm]. The luminous flux describes the amount of light emitted by a light source. It is important to distinguish between the luminous flux of the LED, i.e. the chip itself, and the lamp. These specifications are usually (far) apart, since the luminous flux initially emitted by the LED chip is typically directed through lenses.
In the process, some of the luminous flux is lost due to light deflection and reflections within the spotlight. Therefore, it is always important to know which of the luminous fluxes we are dealing with. Many manufacturers advertise the luminous flux of the light source, but not that of the overall system. The luminous flux [lm] should not be confused with the illuminance [lux]. Illuminance [lux] defines the light output in a given area in lm/m2. Here in the example we look at it with 1lux. The formula for calculating one lux: 