Magnitudes and units

Luminous flux

Amount of light emitted by a light source in all directions.


Measuring unit

LUMEN ( Lm )

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Illuminance

The luminous flux per unit area. (Density of light on a given surface)


Measuring unit

LUX ( Lm/m² )

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Light intensity

Part of the flux emitted by a light source in a direction given by the solid angle containing it.


Measuring unit

CANDELA ( Cd )

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Luminance

Luminous intensity emitted in a given by a luminous or illuminated surface direction. (effect of “brightness” that a surface produces on the eye)


Measuring unit

candela per square meter ( Cd/m² )

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The main difference between Lumen and Lux is that Lux uses a surface as reference. This means that Lux uses a surface to distribute the light flow and Lumen do not use any reference. For example, if we concentrate 1000 Lm in a squared metre, we are lighting the surface with 1000 lux, but if we concentrate also 1000 Lm in a surface of 10 squared metres, we are only lighting this surface with 100 lux.

This means that the lumens of a lamp depends on the surface you want to light and the level of light you need.

Iluminancia​ ​Ejemplo Superficie​ ​Lúmenes
​50 Lux ​Sala de una vivienda familiar ​20 m² ​1.000 Lm
​80 Lux ​Pasillo/cuarto de baño ​6 m² ​480 Lm
​400 Lux ​Oficina bien iluminada ​60 m² ​24.000 Lm