Waiting for the Green Light

While the dominant theme at ISC West was going digital and networking, the 2009 Lightfair International was all about going green—how smart use of lighting can make big reductions in energy consumption. Of course, a large piece of that was cutting down on energy usage by going digital and networking. I heard a couple points over and over at the lectures and at booth visits:

• Lighting accounts for roughly 20 to 60 percent of total energy consumed in buildings (depending on whose numbers you look at). Whatever the precise numbers, it’s clear that cutting down on the energy used for lighting slashes a building’s energy use and cost.

• There are two main categories to look into for cutting electricity used for lighting: higher efficacy (lumens per watt) light sources and intelligent control of lighting.

Everywhere I looked, companies proclaimed that their products were key to achieving these goals. The efficiency folks far outshone (pun intended) the architectural lighting people.

Intelligent control systems need controllable light sources, which preferably can be integrated into a system. The other big piece is the controllers.

Controllable light sources

The easiest to control are light-emitting diodes (LEDs), but the available applications for LED sources are limited by the technology. However, I saw great progress since last year. At this point, LEDs still are limited in their ability to provide general illumination, but given the attention being paid to them, no one doubts that their time is coming soon. According to Michael B. Petras Jr., president and CEO, GE Lighting and Industrial, 50 percent of GE’s lighting research and development budget currently is being spent on LEDs and organic LEDs.

Because LEDs are solid-state (semiconductor) devices, their light output is proportional to the DC current flowing through them. They can be controlled from 100 percent of full light output down to 1 percent.

LEDs are particularly well suited for dimming applications. The most obvious approach to dimming would be linear adjustment of the DC current, but this is not an efficient method, because when light levels are cut back, energy is lost in the controller. With a linear controller, the total power used is roughly constant. At the high end of the range, most of the power is converted to light, but at the low end, most of it is converted to heat.

A nice thing about LEDs is that they don’t mind being switched on and off. They are well suited to electronic switching control technology, which works by turning the current fully on and fully off and adjusting the ratio of on-to-off time to control the average current. This is an extremely efficient technique that is especially easy to implement at the low currents used by LEDs.

Plenty of show floor space was devoted to other energy-efficient and dimmable light sources; for example, Sylvania announced its Powersense electronic dimming ballasts for T8 and T5 fluorescents. These provide a range of 100 to 5 percent for T8s and to 1 percent for T5s and work with either an existing two-wire power line dimmer or a 0–10 volt control signal or both—whichever calls for a lower output will prevail. Sylvania also has a couple of bi-level ballasts, which are more economical to install and provide a choice between full-on or a fixed reduction.

Lighting controllers

Controllers can be used in two basic ways, either for local control, such as in a daylight harvesting system or a scene programmer, or networked into the building-management system.

Watt Stopper/Legrand, for example, was showing its new 0–10 volt wall box controller that can be used to dim or switch lighting loads or raise and lower window shades. The company’s Miro Controls, which include wireless radio frequency dimmers and scene controls, eliminate control wiring and the need for a central processor. They primarily are used to dim compatible 0–10 volt fluorescent dimming ballasts and can provide 1 percent dimming when used with -

T5 HO lamps. The devices, which work in conjunction with a power pack, can control up to 100 ballasts and may be used to power an occupancy sensor, which when connected to the controller, adds Code-compliant automatic shutoff.

Lighting is for people

One of the most important ideas I picked up is that the system components are only part of the green design picture. It is most important to consider what the lighting will be used for and to think about how people actually will use the systems that the designers envision.

Studies have shown that automatic on-and-off occupancy sensors typically save less energy than lighting that has to be switched on manually and only gets turned off by the occupancy sensor. When the person entering the room has a choice of turning the lighting full on or at a reduced level, he or she often chooses the reduced level if there is enough daylight. Giving people some input in the control system turns out to be very effective in the long run.

BROWN is an electrical engineer, technical writer and editor. For many years, he designed high-power electronics systems for industry, research laboratories and government. Reach him at ebeditor@gmail.com.

About the Author

Edward Brown

IBS Columnist and Freelance Writer
Edward Brown is an electrical engineer, freelance writer and editor who draws on his years of practical experience designing industrial processing and high-power electronics systems. In addition to writing the Integrated Building Systems column for E...

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