MH Controls Corner: Simple Guidelines to Ensure Correct Daylight and Occupancy Sensor Operation

There are two fundamental considerations that must be made to ensure that lighting control daylight and occupancy sensors operate correctly. First, the correct device has to be selected to fit the application, and second, the device must be installed in the correct location. The different types of devices, and what to use for particular applications, has been discussed in previous Controls Corner articles. In this article, I will be focusing on guidelines to make sure that devices are installed in locations that will ensure their correct operation.

Installation of devices can be challenging for contractors, as they are trying to install devices based on diagrammatic engineer’s drawings that are not necessarily coordinated with HVAC, fire alarm, public address, and all kinds of other systems competing for the same ceiling space. It is important to know how far an occupancy or daylight sensor can be moved to accommodate that air diffuser before it will compromise the operation of the lighting control system.

The first, and one of the most important, places to look is at the manufacturer-specific lighting control shop drawings. Not only are the engineer’s documents diagrammatic, but they are not designed based on all of the intricacies of the particular control system provided. The device layouts in our shop drawings are still diagrammatic in nature, and are not coordinated with the other trades, but do show all devices that need to be installed. Also in the shop drawings are specific wiring diagrams, installation details, and cut sheets that indicate installation locations, guidelines, and coverage patterns.

There are also some specific rules that should be followed for particular devices:

Occupancy Sensors:

• Occupancy sensors should never be installed within six feet of an air diffuser. This will lead to lights being held on, particularly when the sensor uses ultrasonic sensing technology.
• Sensors must be placed to achieve full coverage of the space that they are in. Sensor coverage patterns are located in the cut sheet for the particular sensor. Many of the ceiling-mounted sensors that we use have a coverage circle with an approximate diameter of 30 feet. This means that there should be no portion of the space that is more than 15 feet from a sensor.
• All sensors will have time delay and sensitivity adjustments. If the lights are staying on, adjust the sensitivities down, starting with ultrasonic in dual technology devices. If the lights are turning off when occupants are in the space, adjust the sensitivities up, and increase the time delay.

Daylight Sensors:

• The installation location required is different for open and closed loop daylight sensors. Open loop sensors should see natural light only, while closed loop sensors should see both natural and artificial light. More information on daylight sensors can be found in here.
• For closed loop sensors, the sensor will pick up light directly below the sensor. The location at which the sensor is aimed should be on the work plane or floor near the light fixture that is controlled.
• For open loop sensors, it is critical that the sensor “point” out the window. These sensors typically look down at a 45 degree angle. The sensor needs to be installed in a location where the 45 degree angle will look out the window and not at the floor or wall.
• Be careful to not install daylight sensors directly above pendant fixtures with an up-light component.

Following the above guidelines will go a long way to ensure that the lighting control system works correctly. This will greatly reduce rework that will be required during system startup, and callbacks after the occupants have moved in.

This article was written by Clint Conley, our Lighting Controls Department Manager. Clint can be reached at 720.904.8554 or clint@mhlighting.com.