What are cut-off and shielding angles?

The angle, measured up from nadir, between the vertical axis and the first line of sight at which the bare source is not visible. The greater the cut-off angle, the greater the visual comfort provided by the luminaire due to improved glare control. The same lighting layout of downlights produces different distributions on the wall.

 

A cut-off angle of 40° gives the best possible compromise between the necessary horizontal illuminance on the floor and vertical illuminance.


Vertical illuminance is important in places such as salesrooms where products should be well illuminated. On downlights with a 30° cut-off angle, the maximum luminous flux is emitted at a high lateral angle.
Due to their narrow light distribution, downlights with a 60° cut-off angle achieve very a high visual comfort for high rooms.


Cut-off angle+ Shielding angle=90°

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