Lighting Controls

Lighting controls, whether manual, automatic, or motion-sensor, are important for managing both energy use and occupant comfort.

Lighting and Building Energy Use

According to the Energy Management Handbook, 7th Ed., building lighting systems consume approximately 20% of the total electricity generated in the United States. In residential buildings, lighting accounts for approximately 12% of the total building energy, and in commercial buildings that amount goes up to 25%, according to a US Department of Energy survey in 2008. These astounding numbers make lighting systems one of the “low-hanging fruit” when it comes to developing Energy Conservation Measures (ECMs) for a building.

Free LEED Exam PreperationThe Goal of Lighting Controls

To save energy in a lighting system, either the bulb itself has to be highly efficient or the lighting system needs to have the ability to dim or turn off all together when artificial lighting is not necessary. The latter is what lighting controls do.

Types of Lighting Controls

The most basic of lighting controls is the simple manual “on/off” switch. From an early age, we learn that it is smart to turn off a light when you leave a room, as the light is just wasting energy and providing light for no one. Manual dimmer switches also allows you to dim the light to the necessary level required, which in turn saves energy as less light is used. There is also a control known as a bi-level or split switch, which allows you to operate different lamps (bulbs) within a fixture that has multiple bulbs.

Saving energy with simple manual lighting systems often requires a change in human behavior, however. Businesses and organizations in large commercial buildings need to make energy conservation a priority and bring awareness to their employees to remember to turn off the lights when they leave a room. Since this can often be a rather large and difficult task (especially in very large organizations), more complex lighting controls were developed to automatically turn off and/or dim the lights for us when artificial light is not needed.

One simple control is a time-based switch, where the lights operated on a time schedule. For example in an office building, a timer could be set to turn the lights on when the first employees come in to work, and off when the last employee is scheduled to leave. A manual override switch could be provided for employees who come in earlier or leave later than the base schedule. This type of control works well in a building that is on a very fixed schedule.

Types of Occupancy Sensors

A slightly more sophisticated indoor lighting control is an occupancy sensor, which automatically turns the lights on when a room is occupied by a person, and off when that person leaves. These controls are able to do this by detecting motion, which can be done in a variety of ways. The primary types of occupancy sensors are Passive Infrared (PIR) and Ultrasonic (US), while Dual Technology (DT) sensors combine both US and PIR technologies.

PIR sensors detect differences in infrared energy in a room, and must have an unobstructed view of the body providing the infrared energy in order to detect it. When a person enters the room, the PIR sensor detects the infrared energy and turns the lights on and keeps the lights on as long as it continues to detect movement in this manner. After a period of time with no detected movement, the sensor then turns the lights off. This type of sensor is well suited for open office spaces, conference rooms, classrooms, or any type of room with a clear line of sight from the sensor to the entryway so it can detect when a person enters or exits the room.

Ultrasonic sensors send out high frequency sound waves which bounce all around the room and back to the sensor. When the sound wave is distorted by motion in the room, the US sensor detects this as movement and turns the lights on. Just like the PIR sensor, after a period of time with no detected movement, the sensor then turns the lights off. What makes US sensors different than PIR sensors is that these sound waves can go around corners and don’t need an unobstructed view. However US sensors do require an enclosed space and work better with hard surfaces in order to reflect the sound waves. Suitable rooms for US sensors include restrooms, storage areas, warehouses, locker rooms etc.

As previously stated, Dual Technology sensors combine the benefits of both PIR and US sensors, which improves the reliability of the sensor and can minimize a false activation.

For outdoor lighting, a photocell control is similar to a timer switch where the lights come on when the daylight levels go below a certain level (at night), and come back on when the daylight raises above that level (in the morning).

Photocells can also be included in indoor lighting applications in order to dim the lights when there is a sufficient amount of daylight available. This is known as a “daylight harvesting” system. This is a very complex lighting control where the lighting levels need to gradually adjust as the amount of available daylight rises, so not to disturb the occupants. This type of system is obviously more suited for spaces that have a high level of exposure to the outdoor environment and direct sunlight.

There are certain types of lights where controls are not really appropriate. For example, high intensity discharge (HID) lamps which require a delayed re-start (which often takes up to 15 minutes or longer) are not well suited for occupancy sensors or dimmers.

Costs, Energy Savings and ROI

According to the Energy Management Handbook, 7th Ed, occupancy sensors can account for lighting energy savings of anywhere from 20% (office spaces) to 75% (warehouses), depending on the exact type of room and sensor utilized.

A Case Study from the General Services Administration (GSA) in 2000 found energy savings similar to those stated in the Energy Management Handbook, with occupancy sensors in private offices reducing lighting energy by 25%, daylight dimmers saving 27%, and a combination of the two saving upwards of 45% of total lighting energy.

A report released by CleanTech Approach (CTA) in 2010 had similar findings of an electrical use reduction of 35-55% by using various types of lighting controls, which resulted in a payback of anywhere from 2-10 years.

It should be noted that while the constant on/off cycling of a lighting control may decrease the overall lifespan of a lighting system, the energy cost savings of using lighting controls far outweighs the additional cost of replacing a lighting system a little more often. In addition, an energy reduction in building lighting will often also reduce energy use in a building’s HVAC system, as it will not have to provide as much cooling to account for the heat load from the lights not on.

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