Control Issues

It's safe to assume that most building owners would not let water run freely throughout their facilities, but most people don't necessarily understand that lighting without effective controls amounts to the same thing—a terrible mess. On the other hand, a lighting system regulated by well-designed controls is an efficient, cost-effective component of a building's operating systems.

In fact, a control system can be the most effective means of maximizing the benefits of good lighting, enabling facility managers to use only as much energy as is required.

Further, proper lighting controls can make a facility a friendlier place, as accessible, well-planned switches and dimmers give occupants options for creating the pattern and intensity of lighting that will make them most comfortable and productive.

Lighting control schemes, however, should always consider the impact on the people working in the space. In other words, lighting controls that do not take into account user needs become more of a hindrance than a help. Avoiding this kind of situation is the responsibility of the system designer and the building operator. Consequently, controls must be accessible and intelligible, as well as have reasonable local overrides so people are not "left in the dark."

The best time to make decisions about lighting controls in a facility is right now. Undoubtedly, it is much easier to do so during a preliminary design phase, but it is never too late to harvest the savings and operating benefits produced by properly applied lighting controls. The first step is to look at either how lighting is currently being utilized, or will be used.

Typically, lighting is provided for occupant safety, comfort and convenience, as well as to help create a building's image or identity. Each of these uses represents the beginning of a control strategy and the building can be divided into areas or zones according to lighting usage. A simple way to determine where these divisions are is to ask the following questions: Who will be using the area? What will they be doing there? What time will they be there? And for how long?

Interior spaces can be categorized as follows:

• Circulation areas—corridors, stairs and lobbies.
• Common facilities—dining areas, meeting rooms and fitness centers.
• Support spaces—mechanical rooms and storage rooms.
• Work areas—offices and laboratories.

Similarly, exterior lighting can be divided into usage areas such as parking lots or garages; walkways and building entry points; and landscape or accent lighting.

Next, consider that each area represents a different function. Some spaces contain areas that are frequently occupied, some are rarely occupied and some—such as the offices, labs or meeting rooms—are occupied only during specific hours. The activities performed in these areas vary, so it follows that their lighting requirements will also vary. Consequently, the lighting for each area should operate according to a schedule suited to its needs. Similarly, different intensities can be maintained throughout this schedule, according to the activities they must support.

Once divisions are established, the next step is to examine available products. In the simplest analysis, lighting control systems come in two types: those that turn lights on and off, and those that vary intensity. On/off controls come in various forms. The most common types are: toggle switches, time clocks, photocells, relays and contactors. Time clocks provide scheduled control of lighting loads, and photocells react to changes in the ambient light level. Both continuously repeat their preset program of operation—barring an equipment failure—without any additional input. Switches, relays and contactors require an operator, either an individual who throws a switch or a control device—such as a microprocessor, photocell or occupancy sensor—to make the contact.

An occupancy sensor lighting controller is a light switch designed to detect motion within a space using either a field of ultrasonic sound or infrared light. Sensor types are made with a variety of field shapes and orientations designed for different shapes and sizes of rooms. Within the range of its field, an ultrasonic sensor detects fine movements and can even "see" over hard surfaces, such as partitions in restrooms and workstations. However, at the limits of this field such movements may not be detected. Also, an ultrasonic sensor can be fooled by air movement near a diffuser.

The other type, an infrared sensor, detects movement across the bands of light that it emits. Consequently, it only detects large movements within its line of sight. In all cases, infrared occupancy sensor systems must be "tuned" after installation. This involves adjusting sensitivity and time delay settings as is appropriate for the space. Most suppliers of occupancy sensors offer this post-installation service.

The spaces where occupancy sensors are most commonly used are conference rooms, private offices and restrooms. Areas that are usually occupied, such as large open offices, produce less savings. In any case, end users will ultimately see savings in their facility's kilowatt-hour energy costs but not necessarily in monthly peak kilowatt demand charges, because the sensors don't actually reduce the connected load of the lighting system.

Another question the owner must answer is: who will be allowed access to the switch? This answer can be determined by the lighting function. For example, safety lighting is too critical to be left to a human operator, so some form of automatic control is best. However, since this lighting can be on for long periods, the control strategy should include a method to limit its use. A timer or photo device can step down the light intensity in a parking garage by energizing fewer fixtures during daylight hours. Then, during periods of low usage, a timer, coupled with an occupancy sensor, can be used to drop off a portion of the walkway lights, or keep corridor and stair lighting off when unoccupied.

Office lighting is a different issue, as provisions must be made for direct occupant control. Although some areas operate on a regular schedule, off-hour use is common. Therefore, strict time control of the lighting is unacceptable. This is also true in common areas such as meeting rooms or reception areas. Toggle switches are the typical solution, but occupancy sensors may be the best choice.

Another useful device in areas with incandescent lighting is a dimmer. In the past, dimmers were only considered to be an amenity for high-end spaces. However, dimmers also offer an opportunity to conserve power usage. Modern dimmers are electronic and use semiconductors to vary the fixture input voltage, and hence light output. This also varies the amount of power served to the fixture and reduces operating costs. Reducing voltage to an incandescent source also slows the deterioration of the lamp filament and extends its life. Consequently, the total savings in kilowatt hours and lamp replacement can be dramatic. A 10% reduction below a lamp's rated line voltage will produce a nearly equal reduction in power consumption and reduce the light output by approximately 30%. However, this will also extend the lamp to nearly four times its rated life. Any space where incandescent lamps are used will benefit from dimmer installation.

A programmable lighting controller interfaced with a building automation system (BAS) provides an excellent means for saving energy. This control strategy divides the facility into functional groups and programs the system to turn lights on and off according to the normal occupancy schedule for each group. Each lighting circuit is controlled by a relay that responds to the programmed directions. The controller can be fitted for local override if people enter the area off hours, and can account for changes in each area's schedule. The interface to the BAS can be used to report operating profiles and may offer the opportunity to optimize HVAC usage in each building area. (Go to "Deep Links" at www.csemag.com for a case study illustrating this technology.)

Another aspect of the lighting design, lighting circuits, should also be configured according to the control strategy. Controlling lighting on a per-circuit basis is less costly, so separate circuits should serve each control group. In other words, the corridor lighting should not share a circuit with the offices. Similarly, walkway lights should not be on the same circuit as landscape lights. Each functional piece of the facility offers a different opportunity to control lighting use, but mixing the circuiting may complicate a control device's wiring or limit future options.

The growth of computer networking has had a great influence on lighting control systems. In the past, each electronic lighting control system stood alone in a building, especially when built by different manufacturers. Therefore, the conference room dimming system had no communication with the relay system that provided programmable on/off control of the office lighting. At best, they could both report their status to a centralized BAS. However, this has changed because most control manufacturers have started incorporating two communication standards into their systems.

Almost 15 years ago, the United States Institute for Theater Technology (USITT) developed a standard called DMX512—a method for digital data transmission between control systems and dimmers. The standard covers electrical characteristics, data format, data protocol, and the design of cables and connectors. It also allows control systems to talk to dimmers, relays and automated lights made by different manufacturers. The other standard comes from the computer industry—the RS232 data port. This is the serial nine-pin connection that sits at the back of a computer. RS232 is a transmission protocol that allows analog data communication between systems. Relay closures and sensor readings can all be translated into program instructions for the system so architectural control manufacturers can provide an RS232 connection.

Theatrical control manufacturers use DMX512 and, increasingly, the top manufacturers can provide both DMX512 and RS232. This means that it is possible to link all controls together and access each system from another, or from a computer. This increases the flexibility and efficiency of all systems. For example, the building automation computer can tell the relay system to turn on Preset Scene 4 in Conference Room 5 at 3 p.m. on Monday the 22^nd. It can also make sure that all unnecessary lighting—including the conference room dimming systems—are turned off at the end of the work day.

Most recently, lighting control companies and ballast manufacturers have been working with new protocols that can provide digital control and monitor each lighting fixture in the building. Digital Addressable Lighting Interface (DALI) was developed in Germany and has been promoted worldwide. Several manufacturers have adopted DALI or similar standards as a means to provide a seamless interface between the components of an integrated lighting system. For example, in a fully developed system, each fluorescent lamp ballast is given a digital address. This means that each ballast can be accessed for on/off control or dimming through a standard computer network interface. The whole system can be mastered through a BAS and everyone in the building can control the lighting in their area through their own computer. Each addressable device also reports its status to the operating computer. This means that fixture locations are mapped in a building management system and tell the maintenance staff when they need to be serviced. In effect, lighting control becomes a building-wide system consideration, not just a stand-alone or specialty application.

At the same time, fully digital addressable lighting systems are not yet common and their cost and complexity make them an intimidating retrofit consideration. Very few companies provide all the components—ballasts, dimming modules, network interfaces—that comprise a system, and integrating components made by different manufacturers is still not quite seamless. However, digitally addressable systems are the future of lighting control.

Another recent innovation in lighting control technology—automated lighting fixtures—has enabled show-lighting designers to add that extra visual thrill to their designs. Small motors with microprocessor controls let the designer program pans, tilts, color changes and moving projections into the fixture.

Until recently, using automated fixtures in a commercial building has been difficult. The theatrical fixtures have always required more tender loving care than the typical building maintenance staff is prepared to give. But now several manufacturers offer architectural versions of their automated fixtures. The fixture construction is sturdier, and they are rated for indoor and outdoor environments. Their programming is simpler and more reliable, and they use long-life metal halide lamps. The on-board fixture programming can be networked into the building system using a DMX512 protocol.

It is doubtful, at least in the foreseeable future, that automated lighting will be commonplace in the standard working environment. However, a few fixtures, properly placed, can create a dynamic identity for a facility.

Once all the lighting control issues have been identified—visibility requirements, operating schedules, life-cycle costs and user interfaces—end users can begin to develop a control program that suits their needs. The hardware can be as simple as local wall switches, or as complex as networked digital processors, but the return in energy savings and user comfort can be rapid and lasting.