Signs placed at all emergency exits along escape routes should be so illuminated as to indicate the direction to a place of safety in an unambiguous manner. [PNEN1838:2005]
Exit and direction signs should be clearly visible from anywhere along the escape route. All signs indicating emergency exits and escape routes should be in the same colour and format, whereas their minimum illuminance should be 2 cd/m2.
As people in the building may not be familiar with its layout, internally illuminated, permanently powered safety signs are recommended.
Note that internally illuminated safety signs are visible from a greater distance than the same size signs illuminated from the outside.
d [m] – viewing distance (maximum distance at which a sign is visible and recognizable)
p [m] – height of sign
s – constant value: 100 for externally illuminated signs and 200 for internally illuminated signs