Market Intelligence

Green & Sustainable Construction

Daylighting Controls

Controls are required to realize the energy and cost savings of daylighting by dimming or switching off the artificial lighting.

Available daylighting controls are of two types: multi-level switching or continuous dimming.

Multi-level Switching

Multi-level switching turns off some or all of the lights in response to daylight. Equipment consists of a light level sensor and relays. Standard lamps and ballasts are utilized. For example, a three-lamp fluorescent fixture with a one-lamp ballast and another two-lamp ballast would have four lighting levels: all off, one on, two on, or three on.

The switching of circuits on and off is noticeable to occupants, and a potential cause for complaints. Lighting circuits must be laid out such that they correspond to the natural light levels in a room. Rows of lights would be laid out parallel to the windows such that lights near the windows could be off, while those far away from the windows are on.

The difficulty and expense of reconfiguring lighting circuits limits the use of multiple-level switching in retrofit projects.

A multi-level control module would cost around $400 and could control several zones. Each zone would require a photocell sensor at a cost of $110 and power relay at a cost of $180.

Continuous Dimming Controls

Continuous dimming controls address the shortcomings of multi-level switching, albeit at a higher cost.

Equipment consists of a light level sensor, which supplies a low-voltage control signal to each electronic, dimmable ballast. The electronic controls within the ballast modulate light output in response to the signal from the sensor. Since the control wiring is independent of the power wiring, there is no need to reconfigure the power circuits in a retrofit project, although installation of the low-voltage control wiring is required.

A dimming control module would cost around $150 per zone controlled. Typical size of a lighting zone is about 2,500 SF. Each zone would require a photocell sensor at a cost of $110. The dimming ballasts cost around $35 apiece (check these prices they seem low). The cost of dimmable ballasts is significantly higher than non-dimmable electronic ballasts, however some of the newer self-addressing dimmable ballasts are showing promise in driving down the market price.

Placement of Controls

Placement and orientation of the light sensor is of paramount importance in daylighting system design.

Usually, the light sensor is located in the ceiling overhead (measuring light reflected off the work surface below, between the windows and the light fixtures to prevent artificial light from causing control feedback). Daylighting sensors can also be built into the switch plate, mounted on a vertical wall, providing an easy and inexpensive retrofit.

The desired light level is selected by programming or dip switches on the sensor. Lower light level settings will result in higher energy and cost savings, since daylight will allow artificial light to be off for more hours of the year. (If necessary, task lights can augment daylight to provide the required light level on the work surface.)

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