In the past, businesses trying to economically provide a well-lighted workplace had a choice between lighting control systems with dimming functions and systems with switching functions. Now that the Digital Addressable Lighting Interface (DALI) protocol has entered the market, those same businesses have both functions and greater control at their disposal in one system.
Developed by a group of U.S. and European lamp/ballast/fixture manufacturers, DALI is a nonproprietary protocol standard that provides a means for digital communications between a controller and an individual lighting fixture that contains a linear fluorescent, compact fluorescent, or incandescent/halogen lamp. The system borrows digital control signal technology from some photosensor-ballast systems to address each fixture individually through a 2-conductor digital control circuit. As a result, end-users can create or re-create different lighting scenes without rewiring the system.
Digital control transmission is free of noise or interference on the conductors, assuring the reliability of the control signal. In addition, DALI converters are available for integrating components with a separate 1V to 10V analog control circuit, another feature of some photosensor-ballast systems. The Table above compares the two types of control systems.
DALI is designed primarily to provide a simple, flexible lighting control scheme, making relatively slow data rates adequate and eliminating the need for expensive components. You can also connect the interface to a building management system via a gateway, allowing you to monitor the lighting system from a central control desk in the building.
The cost of a DALI system is somewhere between that of a 1V to 10V analog control system and the more complex bus control used in building automation systems.
Digital control is the wave of the future. Because each fixture, or ballast, has its own unique address, you can establish a variety of control functions with a DALI system. Any fixture can belong to more than one control group in a layout of ceiling fixtures. DALI is a two-way system, so you can “instruct” each ballast to send back a status report. The system also allows you to coordinate dimming ballasts to reach the same dimming point simultaneously — even if they started at different lighting levels.
In addition, each ballast can turn its own lamp on and off without the use of low-voltage relays, eliminating the limit of switching operation.
How the system works. The controller configures, controls, and modifies components of the DALI system. Using the control circuit, it applies the master/slave principle to communicate with all the lighting system components. The controller sends information on lighting group assignments and scene functions to the memory portion of the ballast's microchip, where the information is stored.
The lamps that can be controlled include the T5 and T5 HO, T8, 18W to 42W compact fluorescent lamps, and the 40W and 50W long fluorescent PL (Biax) lamps. You can access the DALI system by a PC or a Palm OS device. The ballast, which accepts either a 120V or 277V supply, uses a soft-start procedure when the lamps are switched on.
Let's refer to a practical example to see how the DALI system can set up various light levels in a multipurpose office. The Figure below shows a 40-ft×60-ft room that holds workstations for eight people and a conference table. Five rows of 2-ft×4-ft recessed luminaires parallel to the four windows provide ambient lighting for the entire office. Each luminaire has three 4-ft T8 fluorescent lamps and an addressable ballast. A photosensor is located in the ceiling at each of the three rows closest to the windows (Group 1, 2, and 3) to detect the daylight level.
Lighting control is provided for three situations:
The luminaires operate continuously. The constantly functioning photosensor unit determines the daylight level in the room and dims the fluorescent lamps in the three rows of ceiling luminaires closest to the windows, saving the office electric energy during the day.
Overhead projector presentations require greatly reduced ambient light levels. Only a minimal lighting level is necessary near the exit door and over the conference table for people to take notes.
A third lighting scene, set up at the end of the presentation, encourages discussion. This lighting scene highlights the conference table and sets a low level of illumination throughout the rest of the office.
This example makes it clear the office's 20 luminaires can be combined into a variety of groups that are completely independent of the branch-circuit wiring of the luminaires. A wall-mounted station uses a central function switch and four scene and group function switches to control the lighting scenes.
In this basic configuration, the system can establish up to eight groups with four scenes, including a constant lighting scene. A more advanced system supports 16 groups and five lighting scenes.
The demand for comfortable working environments in business facilities is on the rise, and new technologies like DALI systems are lighting the way to a better workplace.
Sidebar: Electronic Ballasts Rule the Roost
Established now as the industry's standard fluorescent ballast, the electronic ballast (EB) can be specified with a range of ballast factors, and with operating characteristics for different applications. An EB uses semiconductor components to raise the electrical frequency (20,000 Hz to 60,000 Hz). Delivering alternating current at these higher frequencies is a more efficient way to excite the gas mixture in a fluorescent lamp, often raising the lamp efficacy about 10%.