![]() Based on the measured illuminance, it dynamically adjusts the lumen output of the electric lighting systems to maintain an optimum luminous environment. The closed loop system detects both daylight and electric light, and has the ability to adjust for sky conditions which fluctuate over the course of the day due to the continuous apparent movement of the sun and the changes in atmospheric conditions. In a closed loop system, the photosensor must be located within the zone that it is controlling and so it is affected by both daylight and electric lighting. Closed loop systems are generally utilized in indoor installations where visual comfort and task performance are of paramount importance. Open loop systems also find their use in interior applications where daylighting is used only to address basic visual requirements and does not need to consider the dynamic nature of daylight. ![]() Outdoor photocontrols are always open loop since they serve only to trigger a system action and switch lighting between dusk and dawn. It accounts for sky conditions and is not influenced by the electric lighting that it is controlling. In an open-loop control system, the photosensor does not react to changes other than the outside daylight level. ![]() Control strategyĭaylighting control strategies may be implemented using “open loop” or “closed loop” systems. A similar concept known as dusk-to-dawn control is commonly used in outdoor lighting, where outdoor wall lights, security lights, street lights and area lights are turned on at dusk and off at dawn based on real-time measurements of daylight levels. This control strategy uses information provided by photosensors as input to controllers, which then use algorithms to adjust lighting levels in discrete steps (on/off switching), in large, perceptible increments (step dimming), or in small, imperceptible steps (continuous dimming). Daylight harvesting, which refers to the adjustment of electric lighting based on available daylight, is a prime consideration in building and space design. In indoor environments, the presence of daylight can also support visual needs and offer significant physiological and psychological benefits. Minimizing energy consumption and reducing carbon footprint are two apparent benefits of daylighting. The role of electric lighting in daylighted spaces, regardless of whether they’re indoor or outdoor areas, is to complement daylight during daytime and deliver the required illuminance during nighttime. Daylight harvesting and dusk-to-dawn control When the change in photocell illuminance exceeds an established threshold, a photosensor signal is generated to control either a directly interfaced luminaire or a group of luminaires that are network connected and designated with a common zone address. A photocell can produce an electrical current or resistance proportional to the amount of light that strikes it. It controls luminaire operation to achieve additional energy savings in response to the amount of natural daylight detected. A typical photosensor or photocontrol is comprised of a photocell along with a controller which implements the conversion and communication logic. It’s also referred to as a photosensor or photocontrol which, however, technically describes the whole sensing system. A photocell is a circuit element inside the ambient light sensor (ALS) that converts incident radiant energy into an electrical signal for daylight harvesting or dusk-to-dawn control.
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