Dimming control and occupancy sensing

Closed loop systems are designed to provide a constant level of desktop illuminance. However, as the level of outside light fluctuates, so individuals may wish to vary desktop light levels to minimise contrast. On a bright day a constantly lit desk would appear gloomy.

There are obvious advantages to light switching which is responsive to a human presence, but even this technology is not devoid of problems. The adjustment of the sensors is a matter of fine tuning. For example, they may not be sufficiently sensitive to the movements of people engaged in high concentration tasks. Alternatively they may be so sensitive that passers-by trigger the switch causing a distraction. In practice it is often difficult to locate sensors to suit occupancy patterns and work requirements especially in open plan offices where workstations may frequently be relocated. The ideal solution is to rely on manual switching for the 'on' and automatic switching for the 'off'.

Occupancy sensors achieve their optimum value in service areas and circulation spaces. These are areas which are frequently overlooked yet they can use more energy pro rata than office spaces. One common fault is that the positioning of switches and sensors does not take account of the contribution of natural light. This is a particular fault in offices with atria. In some of the worst cases activating lights in an office area can switch on all lights along the exit route and in extreme instances, throughout the whole circulation area. A balance should be struck between optimum safety and the profligate use of energy.

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