DALI: Highly Robust Fluorescent Dimming Solutions


By Craig DiLouie

Dimming for fluorescent lamps has grown in popularity in recent years as a strategy to support lighting goals related to visual needs, flexibility, and energy savings. The Digital Addressable Lighting Interface (DALI) standard protocol offers a path to highly granular, flexible, and powerful dimming systems.

Due to the DALI standard, digital dimming offers the possibility of true interchangeability between ballast manufacturers and defines light output for all levels of dimming signals, ensuring consistent dimming performance across all dimming ballasts regardless of type or manufacturer.

Perhaps its biggest advantages, however, are its inherent flexibility and simplified wiring scheme. DALI enables the construction of a lighting network using a low-voltage communications bus. Each ballast becomes addressable in the network. Ballast control can occur locally via control devices and/or centrally from a PC with software. Zoning therefore begins at individual ballast level, providing the highest degree of granularity of control. Each ballast can be zoned separately or placed into controllable groups for larger zones. In addition, lighting fixtures can be rezoned based on changing future space needs without rewiring, providing the highest degree of flexibility.

Initial wiring is also simplified, as shown in Figure 1 (see sidebar). A single set of control leads is connected directly from the controls to all of the dimming ballasts, simplifying initial wiring. Additionally, dimming modules and control panels are not needed for digital ballasts to control light output. Instead, they use a small power supply connected to the control leads and wall-mounted controllers for powering the control loop.

As an additional benefit, the communication path is bidirectional, enabling collection of data about light fixture energy and operating performance.

"Many end-users and specifiers find DALI an appealing solution based on the flexibility it offers, particularly in those
applications where facility space is frequently reconfigured," says Stuart Berjansky, senior product manager, Controllable Lighting for Advance, a ballast manufacturer. He adds that market sales of DALI-based products have been steadily increasing, indicating DALI is gaining a foothold in the specification community.

Digital dimming is sometimes thought of as exclusive to large installations, but it can be economical in many small applications as well. Typical applications include small and open offices where users can control their lighting, conference rooms and classrooms that require different lighting scenes for multiple types of use, and supermarkets and certain retail spaces where merchandising and layouts change frequently.

"I have used DALI-based lighting control systems on several projects ranging from 3,000 to 750,000 square feet, with the
most interesting applications being conference rooms," says Rick Miller, president of RNM Engineering Inc. "In each case,
the conference room was a standalone DALI system, which controlled not only the lighting with multiscene presets but
also window blinds, blackout shades, projection screens, projector lifts, motorized doors, and even electrified transparent-to-translucent glass panels."

He adds: "Be creative with the desired functions and then specify a well-defined generic system with DALI as the allowed solution."

Potential disadvantages of a DALI-based control system include a higher component cost, limited number of suppliers, perceived complexity of setup and programming, and the necessity of commissioning the system (although arguably all fluorescent dimming control systems should be commissioned). These challenges have inhibited DALI-based technology
as an alternative to traditional analog-based dimming technologies. In addition, to integrate a DALI-based control system into a building automation system operating on a protocol such as BACnet, a gateway device is required.

"As with many lighting technologies, particularly the more niche or sophisticated ones, adoption occurs over time and is a function of the market's growing acceptance and comfort level with the system's features, functions, and capabilities," says Berjansky.

He adds: "DALI enables a broad range of capabilities, however, and those owners/developers who fully understand the
benefits of lighting control systems will embrace the benefits of DALI."

GRAPHIC: Universal Lighting Technologies Inc.

Figure 1. In open offices, T5HO fixtures provide about 25 footcandles of ambient illumination. Total connected load for ambient and task fixtures is 0.81 watts per square foot, although most task lights are rarely used because ample daylight is provided via the southern exposure.