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Self-commissioning  Photosensor


The LRC conducted a number of research studies and development activities to further advance the use of daylight dimming. These activities include a new type of photosensor and research into the effects of dimming on lamp life.

New Self-commissioning Photosensor
The LRC has developed a digital photosensor that is self-commissioning to meet customer needs for ease of installation and reliable operation, yet is expected to cost about the same as existing products on the market. Funding for the photosensor development was provided by Connecticut Light and Power Company.

Wireless sensor Photosensor wall-switch
Wireless sensor Wall-switch controller
A new, self-commissioning photosensor developed at the Lighting Research Center uses a wireless sensor and a wall-switch with a manual user override and a preference-setting feature.

How It Works
The LRC photosensor uses inexpensive embedded digital logic to carry out an automated commissioning routine and to implement an optimized control algorithm for maintaining appropriate light levels on the workplane. Digital control offers precise, repeatable operation that is difficult to achieve with the low-cost analog designs of existing photosensors. The LRC photosensor separates the commissioning process from preference and operating adjustments, making it possible to commission the photosensor once, at any time when daylight is present, yet still allow the occupant to easily adjust the maintained illuminance levels at any time. The automated commissioning routine involves pressing a button, placing the photosensor on the workplane, and then placing the photosensor at its final location on the ceiling or wall and pressing the button a second time. The whole process takes less than two minutes, during which the photosensor takes readings while switching the electric lights on and off and storing the information in non-volatile memory.

The particular implementation of the LRC photosensor consists of two separate devices: a wall-switch controller and a remote, wireless sensor. The photographs above show the two devices. The wall-switch controller replaces the traditional light switch and controls the dimming and on-off switching of the fluorescent ballasts and lamps. The controller also incorporates a manual on-off switch, a user preference/override input button, and three light-emitting diode (LED) status indicators. The remote sensor is a wireless, self-powered device that senses and transmits light level information to the wall-switch controller via an infrared optical transmitter. The wall-switch controller processes the information according to the programmed control algorithm, and dims or switches the lighting.

The results from a field test of the photosensor prototype showed an average office energy savings of 30% with the photosensor compared with a manual on-off switch.

Though the self-commissioning photosensor is not currently available on the market, the LRC is seeking manufacturers interested in commercializing this product.

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Research on the Effects of Dimming on Lamp Life
The LRC conducted studies on the effects of dimming on lamp life, including:

  • Optimum electrode heating as a function of the discharge current
  • Impact on lamp life of starting lamps when dimmed
  • Allowable dimming range without additional electrode heating

In general, starting lamps when dimmed (i.e., at lower than rated current) is more difficult and can potentially lead to problems with lamp life. To ensure long life, especially when supplemental electrode heating is not applied (e.g., instant start), starting the lamp at its nominal full output level and then dimming it down may be necessary to minimize damaging effects.

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