Lighting Research Center Lighting Research Center

Spatial Response

The spatial response describes the sensitivity of the photosensor to incident radiation from different directions. In other words, what the photosensor "sees." Spatial response is analogous to a luminaire intensity distribution but describes sensitivity instead of output. The LRC has placed photosensor spatial response into two categories: narrow and wide. Each has their benefits and limitations.

Graphical representations of the photosensor spatial response are shown using either polar coordinates or in rectangular, 3-dimensional coordinates. To view the spatial response for a number of different photosensor products please select either the polar or 3-D views.

Spatial response is measured by placing the photosensor on a goniometer, a device that allows precise angular measurement and movement, and measuring the magnitude of the photocell signal for a small, point light source located a fixed distance away. By taking many measurements at small angular increments the sensitivity of the entire field of view of the photosensor can be mapped. The spatial response is a relative measure that ranges from 0 to 1 for different directions. It is calculated by dividing the photocell signal in each measured direction by the photocell signal in the direction of maximum sensitivity.

More information on wide versus narrow spatial responses.

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