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For those who have spent many years in the “BMS” world and consider lighting control as not much more than a series of contacts on an I/O module somewhere, it might be time to pay close attention to DALI !
DALI – (Digital Addressable Lighting Interface) has been around for several years. The general availability of DALI products from various manufacturers and the adoption of DALI technology by the industry (designers, installers end customers) has been coming for some time. The days of DALI based lighting designs, as mainstream solutions are here now.
The first word of the DALI acronym is the key “Digital”. DALI takes lighting control into the digital domain leveraging up to the minute digital processing and communications technology. DALI is essentially very simple in its concept and use, however, that simplicity is built upon the latest that technology has to offer. There are many features and benefits of DALI lighting control, this document is intended to give some background on DALI origin, an overview of the technology and insight as to how and where the technology might be used.
DALI came about via a collaboration of several lighting manufacturers back in the late 1990’s. It was obvious then that lighting control needed to be part of the digital revolution. The other important point determined at that stage was that this digital technology needed to be open to all and ideally adopted by many product manufacturers as possible. DALI is now an International Standard (IEC 62386) and is referenced in several other IEC standards. An important point to note from the outset is that DALI is not a system of lighting control as such, it is a protocol adopted in relevant lighting control products and systems. Another important point is that DALI is open and it is adopted by most of the relevant lighting product manufacturers. Now, in this industry the word “open” is used in almost every sentence and I am one of the biggest critics of so called “open systems” that actually incorporate proprietary implementations of open protocols and therefore are not open at all. DALI is a solid and robust protocol. One of the best tests for the correct implementation open standards is “interoperability” of different products from different manufacturers. At this stage the interoperability test for DALI products appears largely intact. This has not stopped some manufacturers from adding “features” over and above the DALI standards to distinguish their products from those of their competitors, more on that at another time.
DALI The Basics.
The diagram below shows a typical DALI schematic.
The wiring for a DALI light fitting is typically five conductors of electrical lighting cable. Active – neutral – protective earth plus two conductors for DALI communications D1 & D2. These conductors are usually the same type as the electrical power conductors (active, neutral and protective earth) and may even be inside the same cable sheath as the power conductors. The D1 & D2 cabling is referred to as the “DALI Loop”. The DALI Loop with DALI devices connected is often referred to as a DALI Network. A DALI power supply is needed to power the DALI communications on the D1 & D2 circuit. The digital communications in DALI (1’s and 0’s) is achieved by devices clamping or shorting the DALI loop. For this reason it is very important to note the maximum DALI power supply total on any single loop is 250mA. Another basic and important point is that DALI ballasts, transformers, drivers etc switch and dim lighting loads at the fitting/ballast. There are no switch wires to run down walls and there are no centralized switching or dimming modules back in a switchboard. Each DALI light fitting has constant power connected and each DALI unit controls the load directly. For those of you with lighting controls experience of a centralized nature like the Clipsal C-Bus , Vantage, Lutron, Crestron, Dynalite, etc, you can liken DALI technology to taking the centralized switching and distributing the control and intelligence to each and every light fitting. This does present some challenges in terms of system maintenance, however, this point also presents very powerful and efficient lighting control opportunities.
Each DALI network can consist of up to 64 individual addressed devices. In practice less than 64 light fittings are connected to a DALI loop to allow connection of other DALI devices like group controllers, scene controllers, PC interface, gateway modules etc. Using less than the maximum number of fittings at the outset also allows for easy and flexible addition of new fittings in the future. In addition to 64 individual addresses each DALI device can belong to 16 groups and have 16 pre set scenes programmed. The wiring topology of a DALI loop is open. For commercial projects DALI installs present unique benefits from the start of the design up to the day the building is knocked down.
For the lighting designer at the early stages of the design there is no need to worry about light fitting groups or circuits. Each DALI fitting is simply wired in parallel on the DALI loop. For projects where lighting is critical to architectural feature DALI products provide very high precision of control, eg a DALI dimming ballast can dim precisely from 1% to 100%. The old days of coarse 0 -10 volt control and series relays switching power are long gone.
The straight forward nature of the DALI install lends itself very well to commercial base building design where office or “tenancy fit-out” details are not known or where it is possible that the tenancy fit-out is likely to change over time. In illustrating this point – referring to the DALI Lighting Schematic, if an office was built around light fittings 1,2,6 & 7 these fittings could be easily programmed to operate as DALI Group 1, from that point on any command associated with Group 1 will result in those four fittings switching and dimming as if they were physically wired on the same circuit. If in the future the office layout was extended and light fittings 11 & 12 were now inside the office area, they would simply be reprogrammed to function as part of Group 1 and now it would appear that fittings 1,2,,6,7,11 & 12 were wired as a circuit. DALI light fittings can belong to more that one group. If you wanted a security patrol or cleaner mode, fittings 2, 6 & 12 could be programmed to function as Group 12 and so on. In addition to the groupings, DALI fittings can be pre-programmed with up to 16 scene settings. Once the fittings are programmed a scene controller or other device simply sends a scene command on the network and units go to their preset values. There are many powerful and smart opportunities available with this technology. A typical scenario includes the introduction of a light level sensor in areas where natural daylight is present. Light fittings adjacent to windows can be dimmed if there is enough daylight present at a given time. Smart DALI controllers / gateways can monitor fittings adjacent to windows which may be dimmed and dim a fitting inside the exterior one with an offset. (More on advanced solutions later.) In many situations especially where high efficiency luminaries like Tri Phosphor T5 are in use, there may be an abundance of artificial light available. Pursuant to light level readings it is possible to commission DALI light fittings so they do not dim above a certain level. Eg, a group of fittings in a certain area can be limited to a 75% maximum level if the resultant lumen output is sufficient. It is important to note that power or dim level and lumen output are not usually linear, this means a 25% reduction in power may result in only 5 or 10% reduction in luminous intensity (light output). This is obviously different for various products. The reduction in power consumed obviously saves energy, cost and heat loading to a given area. So from the basic level of programming and control you can see that DALI presents many flexible and smart opportunities for lighting control.
One of the major attributes of the DALI standard is two way communications. So far we have covered basic commissioning and network commands to DALI devices. Each DALI ballast or light fitting controller has built in intelligence allowing the ballast and lamp to be monitored for fault or failure. If a fault is detected by the DALI control device it is communicated on the DALI network. This situation is particularly useful as the DALI standard has been expanded to include exit and emergency light fittings.
There are many product manufacturers developing network controllers and gateway products for the DALI standard. In Australia a leading product supplier in this category is Dali Control. The BM2500 gateway/controller connects DALI networks to an Ethernet backbone. Controllers are self contained and locally process many functions for the automation and control of DALI networks. An onboard real time clock ensures all time scheduled events operate regardless of whether the controller is on line and communicating with central management software. The controllers serve up DALI fault information via WEB and also incorporate I/O to allow movement sensors, switches etc to control the connected DALI devices. The gateway controllers communicated to central management and emergency light fitting control software. In addition high level interface is possible to other systems via XML over the Ethernet network.
Now we are entering into the domain of systems information and leveraging this information across systems. Building Management Systems, by today’s standard need to be far more than just DDC controls for HVAC. We are in the digital age of information. The Internet gives us all ready and rapid access to all types of information. The Internet and IP networks are ubiquitous, this rapidly advancing communications technology is impacting many aspects of our world. The world of building controls is one domain in particular that is being impacted by this advancing technology. I have a strong belief that building controls solutions that don’t adequately accommodate all the relevant technology disciplines (security, access control, CCTV, fire, metering, HVAC, intelligent lighting etc) and solutions that don’t leverage the valuable information from these systems, will be seen as sub standard maybe even unacceptable, for a world where resources are finite and the environment is under enormous strain.
Systems information from building controls networks is valuable. In many cases this information may be used more than once. When we consider communications networks, industry standard protocols and true systems integration we are in the era of collecting information or data and making good use of it. In the first instance we might monitor the system status of one system and make use of that information for the optimal performance of another system. Eg, the lights go off in a particular area or an area of a security system is armed, if there is a corresponding air conditioning zone the relevant fan coil or VAV unit can be placed on setback mode or shutdown depending on the time of day. For countries like Australia, there are ever increasing requirements for buildings to be energy performance rated Green Star, ABGR. Often development approval and later tenant occupancy depends on this performance rating being met and maintained. For this situation the data we have spoken about can be used from a database for the purpose of analysis, trending and audit reports etc. The flexible control options of DALI and the information available in a DALI install fits in well with this information model.
About the Author
Phillip Hodge - Worked in electronics and communications field for 23 years. Licensed as a Security Consultant in NSW – Australia, having specialized in information security and specialist security systems design for Government and corporate clients for over a decade. In the late 90’s became involved in lighting control and later building controls in general. 2001 to 2006 was the technical and sales manager for Clipsal C-Bus in New South Wales (Sydney) focusing on the commercial application of the technology. For the last year has worked as the Business Development Manager – Building Technology for Integration Control & Engineering (ICE) Pty Ltd, and has helped to strategically position ICE to offer it customers truly open and powerful integrated systems solutions. ICE Website
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