Photosensor Placement Tips – Save Energy, Save Confusion
The use of photosensors is crucial to saving energy, especially in areas where stringent watts-per-square-foot requirements are in effect. California is one such place and here, under Title 24, credits are given for lighting installations with photosensors allowing lighting specifiers greater flexibility to meet the State’s restrained watts-per-square-foot requirements.
As other states move to limit wattage, it is very likely similar sensor credits will soon become the norm in lighting codes across the nation. Therefore, we believe every lighting pro should know how to best use and place photosensors.
But placement can be tricky. And there are many factors to consider when deciding to deploy and place photosensors.
The first decision one has to make is to choose between an open loop and closed loop system. A photosensor in an open loop system responds only to the daylight and is placed accordingly. A photosensor in a closed loop system responds to both daylight and electric light.
As closed loop systems are much more prevalent for indoor applications, we’ll keep our tips to photosensors used in those environments.
Ceiling-mounted Photosensors with Indirect Lighting
When using a ceiling-mounted photosensor with indirect lighting, the photosensor needs to be placed outside the direct cone of light coming from the indirect fixture. A good rule of thumb is to place the sensor above the least illuminated space in a work area, but keeping it as close to the fixture being controlled as possible. This will allow the photosensor to view the overall light in the room and adjust the electric lights to the desired level.Ceiling-mounted Photosensors in DayLighting Zones
When placing a ceiling-mounted photosensor in a daylighting zone (spaces where sunlight penetrates into the room 1.5-2.5 times window head height) keep the sensor 6’-15’ from the window and away from spaces exposed to direct sunlight. Doing so allows the photosensor to “see” in the zone lit with daylighting but not be overpowered by the suns rays. Lighting fixtures in areas with the same daylight throughout the day can be zoned together and controlled by one well-placed sensor.Integrated Photosensors
Using a photosensor that is integrated into lighting fixture is often preferable to using a ceiling-mounted sensor because no separate installation is required and the ceiling plane can remain free of additional mounted devices. There are, however, reasons that make integrated photosensors less desirable. For instance, when using integrated sensors, more sensors may be required as there is less flexibility with sensor placement and fixture zoning.
Once the photosensors have been properly placed, one still has to decide if the fixtures will dim and brighten or simply turn on and off.
Using dimming technology to keep light at desirable levels requires the electric lights to adjust slowly up and down as the amount of daylight entering the space changes. Dimming is usually not perceived by occupants is therefore recommended for work spaces.
On/off control of fixtures by a photosensor means that when the light level reaches predetermined values in a room, the electric lights turn on or shut off accordingly. This change is perceived by occupants and, therefore, is not usually recommended for work spaces.
What other considerations and factors do you take into account when placing photosensors? Comment below and let us all know.
This post is tagged: codes, controls, efficiency, energy, green, light, lighting, school, sustainability, technology
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