Photosensors: Asking the Right Questions

This is Chris Matt, Managing Editor of Print & E-Media, with Maintenance Solutions magazine. Today's tip focuses on photosensors and daylight-harvesting technology.

The value proposition for daylight harvesting is fairly simple: As daylight levels increase in a space, electric light levels can automatically decrease to maintain a target task-light level and save energy. Automatic daylight-harvesting control systems use a photosensor to measure light levels and signal a controller to dim or switch the lights in response to daylight. A photosensor can include a light-sensitive photocell, input optics, and an electronic circuit that converts the photocell signal into an output control signal.

Managers can ensure success when specifying photosensor technology by getting answers to the following set of essential questions:

• Is it compatible with the given controller?

• What control method does the system use?

• What is the sensor's spatial response?

• What range of light levels can it detect?

• How accurate is its signal?

• How far is the installation site from its controller?

• How will technicians commission it?

• How many zones can it support?

• What are the configuration options?

• Can it operate reliably within the given environment &emdash; heat, cold, moisture, etc.?

• Do listing or compliance requirements, such as Underwriters Laboratories or restriction of hazardous substances, come into play?

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