Photosensors are typically small devices and unobtrusive when mounted in the ceiling. Once installed, the visible sizes range from that of a pen cap or golf ball to the size of a standard wall switch. Some photosensors
are wholly contained in one enclosure that is mounted in the ceiling. Others have separate sensor and electronics units. In the latter case, the electronic unit can be mounted at a location that is more accessible than the ceiling for easier commissioning. The figure below shows eight different photosensor products offered by different manufacturers. The two products on the far right have separate electronic units and only the ceiling-mounted part is shown. The product on the far left is an integrated occupancy sensor and photosensor.
In building automation systems, a photosensor often sends light level information to a control module. The control module uses the light level information to set the electric light level. As used in this report, the
term photosensor includes the function of the control module. In other words, any signal processing or logic devices between the photocell and the luminaire are considered to be part of the photosensor.
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