Low voltage photocell sensors provide precise control of lighting based on measured ambient light levels within a space. Basic on/off units signal a connected low voltage power pack to switch lights off when natural light levels are sufficient to maintain desired overall illumination. These units are effective in spaces where simple on/off control is adequate, such as public corridors, entryways, or areas where occupants are unlikely to notice intermittent lighting changes.
Photocells with daylight harvesting capabilities allow for more sophisticated control, gradually adjusting artificial lighting to complement natural light and achieve overall energy efficiency. During periods of significant daylight contribution, connected lighting is dimmed to a minimum preset level, maintaining comfortable illumination while reducing energy consumption. Conversely, in times of low or absent daylight, lighting levels increase to ensure consistent brightness throughout the space. These units can also be configured to signal the power pack to switch lighting off entirely during maintained high daylight conditions. Additional configurable parameters include high and low trim levels, which set maximum and minimum dimming thresholds, and fade rates, which define the speed of dimming transitions.
All photocells offer adjustable ambient light thresholds, or setpoints, allowing the user to select a value from a range of presets or enable an auto-selection mode. In auto-selection mode, the unit determines the optimal setpoint based on measured light levels in the controlled area. Photocells can operate in two main modes: on/off control or daylight harvesting control, either as standalone units or in conjunction with low voltage occupancy sensors. Only a single photocell should be assigned to control each lighting group to prevent conflicts.
On/off photocell control is recommended for public areas where fully switching lights on or off will not disrupt occupants. In this mode, the photocell output signals the connected power pack (typically via a blue wire) to turn lights off when ambient light exceeds the setpoint and to turn lights back on when light levels drop. To prevent rapid cycling, a deadband is maintained at the current light level, requiring the ambient light to surpass the sum of the setpoint and deadband for the lights to switch off.
Daylight harvesting control is recommended for spaces where subtle lighting adjustments are preferred, such as offices or classrooms. This mode gradually dims artificial lighting to optimize energy efficiency while maintaining overall desired light levels. After reaching the low trim level, the unit may optionally turn lighting off completely. Both operational modes support auto-setpoint selection, adjustable high and low dimming trims, and integration with low voltage occupancy sensors for coordinated lighting control.
Physically, these sensors are compact, with a 4.00-inch diameter and 1.25-inch height, weighing 4.75 ounces, and finished in white matte housing. Multiple contractor-friendly mounting options are available, including mounting nipple attachment with integrated hole saw for secure and straightforward installation. Environmental specifications include an operating temperature range of 32°F to 122°F (0°C to 50°C) and 0–95% non-condensing relative humidity, suitable for indoor applications. Units are RoHS compliant, reflecting adherence to environmental safety standards.
Electrical characteristics include low voltage operation at 12–24 VAC/VDC with a current draw of 2 mA. Dimming capacity is 50 mA, compatible with 0–10 VDC ballasts or drivers, and compliant with IEC 60929 Annex E.2. Operational modes include daylight harvesting to low trim, daylight harvesting to off (requiring a power pack), and photocell override for on/off control. These sensors support energy code compliance with ASHRAE 90.1, IECC, and Title 24, making them suitable for modern commercial, educational, and institutional lighting installations where precise light management and occupant comfort are priorities.
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