Generally, the measurement is executed in the plane where the visual task is located. This plane may be horizontal, vertical or tilted. The measuring plane for horizontal illuminance is located e.g.
at a height of 0.75 m above the floor for offices,
on the reference surface specified by EN 12193 for sports facilities,
at a height of 0.2 m above the floor for escape routes,
at a height of up to 0.2 m above the floor for traffic routes, staircases and parking buildings.