What is a lux? How to measure the luminous flux per unit area?

Lux measures illuminance. Its symbol is “lx”.

Practical applications of lux

A Lux number indicates the luminous flux received per unit area. As an example, the human eye operates in a large amplitude of luminous flux:

  • Our full moon night vision is possible from 1 lx
  • During a very sunny summer day, our eyes are subjected to luminous flux of 130,000 lx
  • Our movements require a minimum of 5 lx to be secured
  • We read, write or work easily when the luminous flux is about 150 lx …

To understand this process, it is necessary to consider three concepts: illumination, light (lm) and lux (lx). The first is considered as the luminous flux that affects a certain area; In other words, how much light is coming from a light source on a surface?

To know the answer, we can imagine a lighting process in which a light source emits a certain amount of light; According to the international measurement system, the emitted light flux can be measured from lumens (lm). The higher the number of lm, the higher the illumination intensity provided by the source.

A Lux number indicates the luminous flux received per unit area.

When the light emitted reaches a specific area, the term lux (lx) is used. It is a unit of measurement equivalent to one lumen / m² and with which it is possible to calculate how much lighting affects a given area. However, in order to evaluate the amount of light, it is necessary to take into account aspects such as the dimensions of the space, the height of the luminaire and its distance to the target surface, as well as the photometric data of the lamps and their amount.

It should be noted that if the light source is close to the target area, there will be more lux, but if it is far, there will be less. For example, a luminaire emits two thousand lumens on a surface of one square meter, in this way one will have two thousand lux emitted on this zone, which represents a lot of light. On the other hand, if the same amount of light is used on an area of ​​20 square meters, the illumination of this spot is only 200 lux, ie less light.

To reach a luminous equilibrium, one will be able to use means, techniques and software to calculate it. In addition, the aesthetic and functional aspects should be considered according to the use of each area to be illuminated. The use of luxmeters makes it possible to obtain an optimal level of illumination.