These days, building owners and facility managers have important reasons to use the most efficient lighting equipment and control systems. A new study prepared by Lawrence Berkeley National Laboratory (LBNL), Berkeley, Calif., indicates that today’s lighting control techniques can reduce lighting energy an average of 24% to 38% in commercial buildings.
Because building new power plants is prohibitively expensive in most every locale, energy-starved states, such as California, are demanding significant reduction in energy consumption over the next decade. For example, California’s Assembly Bill 32 requires that commercial buildings reduce their energy consumption 50% by 2018.
To promote ongoing reductions in electrical energy use, local, state, and federal energy codes are continuously becoming more restrictive. The ASHRAE/IESNA Standard 90.1-2010, “Energy Standard for Buildings Except Low-Rise Residential Buildings,” which must be adopted by all states in the United States by 2013, requires not just turning off lighting in unoccupied spaces, but also multilevel dimming for most spaces — no longer are exemptions granted for spaces that have occupancy sensors. It also requires automatic multilevel daylight control for day-lit zones, skylight zones greater than 900 sq ft, and side-lighting zones greater than 250 sq ft.
The standard’s automatic shutoff control requirements must be met if the lighting alterations in an existing building involve the replacement of more than 10% of the connected lighting load. This rule greatly expands the application of the new ASHRAE standard into existing buildings.
A recent news story highlights the importance of lighting and controls in the design and construction of buildings. The Illuminating Engineering Society (IES), New York, is joining forces with the Telecommunications Industry Association (TIA), Arlington, Va., to exchange information and provide standards development in intelligent building systems, energy efficiency, and sustainability initiatives. This agreement promotes a true integration of lighting systems and communications/controls and serves as a step toward achieving truly high-performance buildings, or “intelligent” buildings (see SIDEBAR 1: Standards Development).
Thus, we can look forward to having the lighting systems of tomorrow being able to communicate with other building systems in an interactive manner. A scientist and energy-efficiency lighting expert at LBNL’s Environmental Energy Technologies Division, Francis Rubenstein did a study using a federal building as the research model. It showed that occupant-responsive lighting and personal controls resulted in 40% less lighting energy use than an energy-code compliant baseline system that had low power density but was manually switched.
Rubenstein believes that fluorescent lighting will continue to dominate the general lighting market and that, in the near-term future, solid-state LED and fluorescent lighting will coexist in hybrid systems — in combination with advanced lighting controls, achieving vast improvements in light efficiency. However, let’s look at the basic technology of lighting controls first.
Understanding Lighting Controls
Lighting control can be defined as hardware — and software — systems that regulate the intensity level of the light output in response to a command or action. Today’s lighting controls fit into four main categories, according to their size and function:
- Distributed networked systems offering total lighting control management.
- Scalable panel systems using low-voltage, mechanically held, single- and double-pole latching relays.
- Architectural/commercial control systems handling a variety of control applications and using input devices that vary from keypads to touchscreen controllers.
- Networked devices and wall box dimmers.
In aggregate, this equipment can provide occupancy/vacancy control, daylight harvesting, time scheduling, task level tuning, lumen maintenance, and personal control within a workspace. Ceiling- and wall-mounted vacancy/occupancy sensors, which are in their third generation of development and use a combination of PIR technology and a microprocessor containing advanced logic circuits for detecting motion, can combine motion detection, infrared (IR) remote control reception, and ambient light level detection.
Conceptually, daylight harvesting is a simple process. A photo sensor detects the amount of daylight coming in through the windows or skylights in a building. That light-level information is sent to a control module that directs specific lighting fixtures to lower their light output.
Time scheduling is ideal for controlling lighting where people work a predictable schedule, such as open offices, retail sales floors, and similar applications. It also works for spaces that are intermittently occupied but where lighting should be kept on (such as corridors, lobbies, parking lots, etc.) for safety reasons. A low-voltage control system, in which local controls are wired to a low-voltage relay bank housed in a lighting panelboard, is ideal for microprocessor or time-clock scheduling.
Task-level tuning adjusts the light level to suit the task, thus solving the problem of commercial spaces being reconfigured or repurposed for different users or tasks. Lumen maintenance compensates for the aging and degradation of a lighting system over time. Personal control refers to the use of a PC, telephone, or hand-held wireless device that allows an individual to set a preferred light level for a specific visual task, such as reading or computer use.
Methods of Control
The dimming control of light sources, which may be done in steps or over a continuous range, can be conveniently separated into nine methods:
- Also called load-shedding, step dimming — whether it is two, three, or multilevel stepped dimming — is a reasonably economical method of achieving a reduction in light output in applications where two or more light levels are desired or required by code (see SIDEBAR 2: Demand Response Control).
- Two-wire, analog line voltage, forward phase control (incandescent and other loads).
- Two-wire, analog line voltage, reverse phase control (incandescent and other loads such as LED sources).
- Two-wire, analog line voltage (Power Class 1) for fluorescent dimming.
- Three-wire, analog line voltage (Power Class 1) for fluorescent dimming.
- Four-wire, analog low-voltage 0VDC to 10VDC (Class 2) for fluorescent dimming.
- Two-wire, low-voltage digital control for fluorescent dimming (DALI specifications or similar designs).
- DMX 512 standard for digital communication networks is commonly used to control stage lighting and visual effects, such as fog machines. It is unidirectional and uses EIA-485 differential signaling at the physical layer. Because it is specialized, this protocol will not be discussed.
- Two- wire, pulse-width modulation (PWM) of direct current for LED dimming (to be covered in a future article).
Let’s look at the second through seventh methods in more detail.
The best known and most widely used dimming control device (other than a snap switch), the forward phase control dimmer fits inside a standard, single-gang wall box. Since its development as a practical solid-state dimming device more than 50 years ago, it has seen prolific growth in homes and other locations, rendering the rheostat essentially obsolete. Using either a thyristor or a TRIAC circuit, the forward phase device, which is also called a forward phase cut dimmer, operates only during the last portion of each alternating current half-cycle, clipping the AC sine wave, smoothly reducing the power sent to the resistive load of a tungsten filament. It is typically used for both incandescent and magnetic low-voltage (MLV) transformer loads, as well as neon, cold-cathode, and some types of fluorescent dimming ballasts, along with some LED power supplies, making it the most common method of dimming control.
A second type of wall box dimmer (called reverse phase control or reverse phase cut), using field effect transistors (FEY) or isolated gate bipolar transistor (IGBT) circuits, operates only during the initial portion of each alternating current half-cycle, clipping the AC sine wave. It is typically referred to as an electronic low-voltage (ELV) dimmer, which serves lower-powered light sources and is used for capacitive loads, such as LED drivers. ELV loads have large impedance changes. Although more expensive than a forward phase type, it has little or no audible noise.
The 2-wire, line voltage, analog phase control dimming method for fluorescent lamps uses a relatively economical forward phase-cut incandescent dimmer, and the wiring to the ballast is a conventional 2-conductor switched lighting circuit with the dimming signal delivered through the phase conductor. This control method is ideal for serving existing fluorescent luminaires, and at least three ballast manufacturers offer this product.
The 3-wire, line voltage, analog phase control dimming method for fluorescent lamps uses a specialized type of forward phase-cut dimmer with three conductors: dimmed hot (the control signal), switched hot, and the neutral conductor to serve electronic dimming ballasts. Although it is the oldest fluorescent dimming method, it provides very reliable performance.
The 4-wire, low-voltage, 0VDC to 10VDC (Class 2) analog dimming method for fluorescent lamps is perhaps the most widely used control method. This wiring configuration requires a line voltage switch to shut off the dimming ballasts.
The 2-wire, low-voltage digital dimming method for fluorescent lamps, called the Digital Addressable Lighting Interface (DALI) open-protocol communications system, is similar to a 0VDC to 10VDC system in that it uses a separate low-voltage control circuit. But unlike a 0VDC to 10VDC control system, which sets the ballast output according to the analog voltage level on the control circuit and is unidirectional, a DALI system uses digital bidirectional commands, sent between a ballast and the control system at a baud rate of 1,200 bits/sec. A high SNR (signal-to-noise ratio) enables the signal to overcome a large amount of ambient noise on the circuit without degradation. Operating conditions, such as total hours of use, light level, or failed lamps, can be monitored through the network. The lamp-failure reporting feature allows quick identification of the fixture location, which is especially important in a large facility or in applications where the lamps are behind the lens of a recessed fixture.
Using a non-polarized, 2-conductor, 24VDC cable, carrying a maximum of 240mA, the control wiring for a DALI system can be in a bus, star, or tree topology — or any combination of these. Additionally, the power circuit layout to the luminaires is independent of the control circuit layout, allowing them to be wired separately in the most convenient manner. Because each ballast receives its own digital address, a control zone can be changed without a need to alter either the power wiring or the control wiring. The control conductors can be Class 2 wiring, or the control conductor may be installed in the same conduit as the power conductors. Thus, it would be designated as Class 1 wiring. A 5-wire prefabricated wiring assembly can also be specified.
Digital control (whether a DALI system or something similar) is considered to be the future of linear fluorescent dimming systems (see SIDEBAR 3: Electronic Circuitry Adds Efficiency). Although dimming fluorescent ballasts have been available for years, their high cost has limited their use. But driven by the use of daylight harvesting techniques in new construction, the sale of these ballasts has increased recently. In addition, their costs have fallen dramatically.
Originally developed by four ballast manufacturers in Europe, DALI is now a U.S. standard (NEMA 243-2006, “Digital Addressable Lighting Interface (DALI) Control Devices Protocol”). To help solve the problem of compatibility of components from different manufacturers, NEMA’s Joint Sections Committee on DALI partnered with the California Energy Commission in 2008 to author an expanded DALI protocol called the NEMA Digital Lighting Controls Open Protocol. It essentially establishes an open digital communications protocol for all types of lighting equipment, allowing them to work together.
A number of lighting equipment manufacturers offer a digital dimming system with the same general capabilities as a DALI system; however, they may use their own communication protocols and associated hardware to deliver a complete lighting system. For example, one manufacturer offers DALI-compliant, addressable, 20A, electrically latched lighting relays that allow for the creation of distributed control systems without the cost and space requirements of central panels and home-run circuits.
Energy regulations will continue to prompt building owners to consider lighting controls in each upgrade project. As projects are finished, these systems pay for themselves because of the energy savings, and the people working in the offices are more productive.