Illuminance: What Does It Mean?

How is illuminance defined? Illuminance indicates how much luminous flux (lumen) hits a certain surface. How is illuminance measured? The lux (lx) is used as the unit of measurement. For an illuminance of one lux, there is a luminous flux of 1 Lumen evenly covers an area of ​​1 m², as is the case, for example, with candlelight from a distance of one meter.

It is important to understand that the illuminance does not reflect the impression of brightness, as this depends largely on the properties of the illuminated material. With the same illuminance, dark walls appear much darker than light ones.

What Level of Illumination Should be Used?

Precise guideline values apply to company and public sites, which should be observed at all costs in the interests of occupational health and safety and personal safety! The illuminance required for workplaces depends very much on the type of visual task and can be well over 1,000 lx for precision mechanical or control activities. In operating theatres, even 10,000 lx should be provided.

• Illuminance of escape routes: At least 1 lx in the centre
• Illuminance for car parks: 10 lx
• Illuminance for corridors and traffic routes: 100 lx
• Illuminance in the office: 500 lx at the workstation, at least 300 lx around it.

Illuminance and choice of light source

Pour le consommateur, l'intensité lumineuse n'est qu'indirectement pertinente lors de l'achat de lampes, car elle n'est pas indiquée dans les données techniques ou les descriptions de produits ; après tout, elle n'est créée que par les conditions spatiales sur place. Il n'est donc pas très utile de rechercher l'intensité d'éclairage des lampes à incandescence, des lampes fluorescentes ou des lampes LED. En effet, celle-ci ne peut être considérée que dans le contexte des diverses caractéristiques du produit, des caractéristiques de la pièce et des effets des autres sources lumineuses dans l'éclairage global. En tant qu'acheteur, il faut principalement tenir compte du flux lumineux et de l'angle de rayonnement si l'on veut évaluer l'éclairage de manière réaliste.

Overview: Important photometric quantities

• Lumen: Power of visible light emitted per sec.
• Luminous intensity (in candela): Luminous flux emitted at a given solid angle.
• Illuminance (in lux): Luminous flux incident on a given surface.
• Luminance (cd/m²): Luminous flux emitted by a surface.