(Term of lighting design)
An imaginary horizontal plane situated at the nominal working height in an interior space. Most illuminance and daylight factor measurements and calculations are made for points on this plane.
For office (desk) work the height of the workplane usually is assumed at 0.85 m (33.5 in) in Europe, and at 0.76 m (30 in) in the USA, and for circulation areas (halls, train platforms etc.) at 0.15 - 0.2 m (6 - 8 in).
Building regulations and professional lighting design associations define required illuminance and daylight factor values for a variety of different tasks. They usually also define specific heights of the work plane, where it differs from the standard values.