Engineering Coexistence between DALI Networks and Real Digital Lighting

It has been 400 years since the death of William Shakespeare, who wrote that “All the World’s a Stage”. With the advent of powerful, versatile, colorful and affordable lighting, his words may have come true in a literal sense. Increasingly, today, throughout venues such as retail centers, corporate headquarters, office buildings, hotels, city centers and even private homes, lighting is no longer viewed purely as a means of illumination but as a way to entertain, impress, charm and influence an audience.

Theatres and concert venues have pioneered the art of the digital lightshow over decades. As one of the earliest digital standards for lighting control, DMX512 (Digital Multiplex with 512 pieces of information) – typically referred to simply as DMX – was conceived in the 1980s for entertainment purposes and has inspired generations of powerful theatrical lighting-control systems capable of running complex, high-speed sequences on large lighting arrays. DMX nodes, such as lighting ballasts, are connected in daisy-chain formation as shown in Figure 1. The standard DMX data rate is 250 kbit/s, which has been sufficient to support high-speed lighting effects.

Figure 1: DMX network topology.

A DMX universe contains up to 512 addresses. Designers can reduce the number of addresses required for a given lighting installation, if necessary, by assigning the same address to a group of lighting nodes that are to act in unison. On the other hand, some nodes may require more than one address, for example to control separate RGB channels. Moreover, two channels may be needed to achieve a finer level of control than the standard 8-bit instruction depth. Multi-universe DMX controllers can be used in installations that exceed the capacity of a single DMX universe.

Digital lighting for buildings

Compared with a theatrical or stadium-rock light show, which fundamentally must excite and entertain, the emerging art of managing lighting in buildings such as offices and retail stores began with more modest ambitions. Key objectives were to save energy and provide a comfortable environment for occupants by automating control of on, off and dimming settings.

When the Digital Addressable Lighting Interface (DALI) specification was introduced in the mid-1990s, it brought the advantages of digital control to the commercial lighting scene. DALI is an open standard designed to promote interoperability between products from different manufacturers, and has been covered by the international standard IEC 62384 since 2014. Figure 2 shows how a generic DALI network comprises control gear such as ballasts, control devices such as physical switches or a software application, and at least one DALI power supply.

Figure 2: Generic DALI network architecture for lighting control.

DALI has capacity for 64 addressable ballasts, which can be commanded individually, altogether, or as members of up to 16 groups. The digital DALI data stream contains address and command fields of two bytes each. The commands can be direct lamp-power settings, indirect power commands such as a command to reduce or increase brightness by a specified increment or at a specified fade rate, or configuration commands. Compared to the DMX data rate of 250 kbit/s, DALI is relatively slow at 1200 bit/s. On the other hand, DALI supports two-way communication with lighting fixtures, allowing exchange of diagnostic information. Recent revisions that allow Remote Device Management (RDM) now raise the possibility of capturing diagnostic information across a DMX connection.

For the purposes of energy saving and light dimming within a building, the DALI address range and command set were generous for their day and continue to be adequate for many of today’s projects. DALI has been widely adopted within the building automation industry.

Creative lighting everywhere

The lighting market has advanced considerably since the arrival of DALI. LED-based lighting, in particular, has fostered greater ambition among lighting designers to take advantage of the technology to achieve imaginative effects, such as creating moods or impressing visitors using interior lighting, or making an impression outside the building by presenting dynamic, colorful shows with architectural lighting.

There are a number of options available to help lighting designers realize their goals. DMX controllers have emerged that are optimized to deliver the advantages of the relatively high capacity and high speed of the DMX standard to commercial and architectural lighting, at a lower cost than typical high-end stage-lighting control solutions. The Dialight Colordriver 36 is an example of a dimmable LED driver that integrates a DMX-compliant control interface and is capable of driving three channels of up to 12 LEDs with dimming from 0% to 100%. It is suitable for decorative lighting or dynamic RGB color mixing, and can support pre-programmed color-changing sequences as well as DMX512 dimming. Separate channels for red, green and blue LEDs allow a wide range of color combinations.

DALI-compatible LED drivers are also available, such as the Cree LMD300 driver, which is specifically designed to work with the Cree LMH2 2000-, 3000-, 4000- and 6000-lumen light sources. Moreover, the DALI standard has also been updated, taking into account advances in lighting technology and market demands. The latest DALI2 specification supports extra capabilities and commands, adds provisions such as thermal protection and load shedding, and gives extra flexibility for lightshow designers by supporting selectable dimming curves.

On the other hand, installers are excited about the opportunities for controlling and powering LED lighting across an Ethernet network, taking advantage of the inherently digital nature of LED emitters. Ethernet allows greatly expanded address space and higher data speeds, and is capable of supporting lighting protocols that have more sophisticated instructions. In addition, an Ethernet-based lighting system can take advantage of standard Ethernet structured wiring, which is already installed throughout numerous office buildings. Controlling the lighting via an application running on a PC connected to the network, or wirelessly using a mobile device, is also easy to achieve using standard, non-specialized equipment. Where expansion of an existing network infrastructure is necessary, to incorporate new lighting devices, this, too, can be achieved quickly and economically using standard networking equipment like Ethernet routers or switches like the HARTING HA-VIS ECON 2040B-A.

Progress and Coexistence

When it comes to installing smart lighting systems, and enhancing existing systems to incorporate extra lights or introduce new features, a wide variety of approaches may be viable. Organizations will likely wish to take advantage of their investment in any existing smart lighting. Given the variety of communication standards now available, the lighting industry needs the flexibility to use the standard best suited to meeting the requirements of the current project. This demands access to a variety of converters, for example to allow new Ethernet-based lighting to respond to sensor information from a building-management system linked to a DALI network.

On the other hand, a single lighting console may be required to control lighting via either a DALI or DMX connection. Microchip has created a lighting-control console that consolidates DALI and DMX512 interfaces.  Capable of controlling multiple prototyping boards such as the AC160214 development board via DALI and/or and DMX512 connections. The console is based on a PIC microcontroller (Figure 3), running DALI and DMX512 code libraries with custom control firmware.

Figure 3: Microchip’s DALI/DMX512 lighting control console.

An application note, AN1076, is also available, which shows how to implement DMX512 communications on a PIC microcontroller. The application note presents transmitter and receiver demonstration code that calls a state machine, such as the transmitter state machine described in Figure 4.

Figure 4: DMX512 transmitter state machine to run on PIC microcontroller.

Conclusion

Digital control has provided a key enabler for creative lighting effects. Aided by the arrival of responsive and versatile lighting technologies, such as colorful, high-power LEDs, demand has spread from the theatrical stage to general building lighting. Designers and installers need the flexibility to be able to mix and match digital control techniques, such as DMX, DALI, or Ethernet, to satisfy new customer demands while working within constraints imposed by legacy systems. This can be provided by bridges, converters and consoles capable of interfacing and translating between the different standards.