What is DALI ?

10/06/2009 by David Slade.

DALI stands for Digital Addressable Lighting Interface and is a protocol set out in the technical standard IEC 60929.

DALI is a bi-directional, digital protocol developed by lighting manufacturers for the control of light source levels. The initial application is for control of fluorescent lamps, both linear and compact to be followed by control of additional light sources such as HID, LED, incandescent, etc.

The DALI protocol has been added to IEC60929, and will be incorporated into an ANSI C82 standard. In addition, both IEC and ANSI are working on extending the DALI system to include other products such as occupant sensors and daylight sensors,

Using DALI, a digital standard in lighting control, it is possible to combine easy installation using the existing 1-10 V interface with the comfort of intelligent lighting control. This means that DALI closes the gap between previous 1-10 V technology and expensive bus systems.

DALI is an interface for Electronic Control Gear (ECG). DALI makes it possible to control the ECG digitally and enjoy all the functionality as required. This means that an ECG designed to conform to this standard is able to carry out the commands issued by a control device. DALI has been designed primarily for use with lighting systems. The functionality of every DALI ECG within a lighting system exceeds by far any previous analog 1-10 V interfaces.

DALI was developed by all the leading ECG manufacturers who came together to define the functions of a DALI-ECG and a load conforming to DALI within a lighting system.

DALI was created in the form of an industry standard in order to satisfy all the demands placed on modern lighting controls. Above all, it includes a facility for receiving feedback from the ECGs concerning their current state and also for storing certain scenario values in an ECG. Every DALI-ECG configuration is able to store 16 group constellations and 16 scenarios.

DALI product features:-
· Control via DALI interface (Digital Addressable Lighting Interface)
· Switchable via DALI control wire
· Addressable
· Dimmable from 100 % to 1 % luminous flux
· Power stabilization in the event of mains voltage fluctuations
· Suitable for emergency lighting
· The control input for the DALI interface is robust with respect to over voltage and reversal

More information is available at http://www.dali-ag.org.

The DALI AG, part of ZVEI of Germany, created the openDigital Addressable Lighting Interface standard, and is laid down in the global IEC document 60929

Problems Addressed/Issues

Luminaires and ballasts are supplied by a great variety of suppliers and are connected in various forms:
- independent
- in clusters
- in conjunction with building management systems with many different protocols.

For all these applications the DALI protocol can be used DALI AG is an open digital protocol for lighting ballasts
Approach

Status 

The DALI-protocol is nowadays well accepted in the lighting market for fluorescent- and High Intensity Discharge lamp-applications and Solid State LightingAdditional standardization documents containing protocol-extensions for emergency lighting, HID and low voltage lamp- applications are currently in specification status.

Applications

DALI for Lighting Control

Apart from regular lighting applications (switching, dimming, scene-setting), the DALI protocol also enables users to realise all kinds of lighting-group-clustering, scene-settings, dynamic- and passive-color variation-settings in combination with external digital activators.
Even status-feedback of devices can be monitored.

Building Management Systems
With help of widespread digital-to-digital conversion devices, DALI-driven lighting networks can easily be connected to Building Management Systems.

Plug & Play applications
DALI technology is also massively applied in smaller lighting installations Recently many DALI-based “plug & play” applications have been introduced, for which installers do not need any dedicated training. With these plug & play solutions give a rapid further acceleration of the growth of DALI-driven applications used.

Advantages/Benefits   

Full compatibility of all ballast and luminaire manufacturer with the DALI protocol

Interchangeability of ballasts and luminaires in existing installations.

16 individual groups can be formed out of the 64 addresses
16 light scenes can be defined individually
Limitations  

DALI is specified for 64 single addresses per cluster
For larger groups, beyond 64 addresses, multiplication of groups via a building management system is required.

Communications media

Fiber-optic cabling, bi-directional single-strand;
Powerline, spread-spectrum, 9-95kHz, 100-450kHz;
Powerline, narrow-band, 125-140kHz (BPSK);
TCP/IP, tunneling;
Twisted-pair wiring, bus;
Twisted-pair wiring, free-topology (powered or un-powered);
(some of the above are ANSI/EIA/CEA or EIA/TIA)

Other non-standardized media include:
Infrared;
Coaxial;
Radio Frequency
Communications rate
OSI layer(s)

System Description
Main DALI features and benefits compared to 1-10V analogue control systems
•    Individual control of fittings: each unit in the DALI network has it´s own individual address, therefore it is possible to communicate directly to the components in the fittings
•    Multichannelling use: through only one pair of control cable it is possible with DALI to control several different groups of fittings
•    No mains switching needed: the lights can be switched off by commands coming directly from the DALI control system making the mains switch unnecessary
•    Back-channelling: the information flow is bidirectional with the DALI system. Instead of only giving commands about the light level to the fitting DALI system enables also information feedback on the condition of the fittings. the fitting can transmit information about:-
o    whether the light is switched on or off,
o    the pre-set light level
o    the ballast condition
•    simple DALI wiring: the cabling consists of a simple two wire cable, independent of any building topology between the units in the system
•    Easy system re-configuration: once the system is installed and configured it is very easy to change the functioning of the system, changing of scenes and functions of lighting is only a matter of programming and needs no hardware changes anymore
•    easy to add new components: when the lighting system needs to be enlargened new components can be added anywhere in the DALI system, no wiring configuration rules apply on the DALI line in this aspect.
Main differences between DALI and building automation buses
•    DALI has a limited system size (64 addresses).
•    DALI is meant only for communication in lighting systems as BMS includes other functionality as well (HVAC, alarm systems…)
•    A BMS system commonly has unlimited expansion possibilities, which DALI does not have
•    DALI is not competing against BMS systems, it is only complementing them through an interface

System Guidelines

Functional compatibility
Compatibility of ballasts is guaranteed by the standard. For other units, like sensors and controllers the compatibility ensurance is in process and the and a standardization will be achieved. Compatibility has always to be ensured when a system is being designed.

System size
The maximum number of individual addresses available in the DALI standard is 64. The maximum DALI supply current is stated as 250mA maximum.

Maximum ballasts in a system
Up to 64 individual ballasts can be connected in a DALI line without exceeding the system node or power supply current limits. This, of course, does not allow for any DALI control devices to be connected to the system.

Ballasts and control units in a system
If control units using the DALI protocol are to be used in a system then the system size will be limited to either 64 nodes or 250mA total system current (whichever value is reached first). When a DALI system is to be constructed containing both ballasts and control units it should be ensured that these limits are not exceeded. If the system size exceeds the limitations there will be problems due to reduced signal integrity ? some devices may fail to communicate or respond to commands and the system operation will become unstable.

Routing
The maximum voltage drop on the DALI line may not exceed 2V, resulting in a maximum line length of 300 m, between the DALI components furthest apart.

Good practice
For the above mentioned reasons it is the task of the system planner to consider the power consumption of each component used and to plan the system in such a way that the system limitations are not exceeded.

Electrical Guidelines
Voltages and currents
In the DALI standard all values are specified at the control pins of the ballast. For the full system the situation is slightly different. In general the control line voltage in a DALI system is normally 16 V (between 22,4 and 9,5 volts) when there is no communication (idle state). This voltage is supplied from an internal DALI power supply. The digital signal becomes low when the voltage level in the DALI system becomes zero (-6,5V - 6,5V)

Supplying the system
In a DALI system the maximum system current is limited to 250mA, which is supplied from additional power supplies. This is to keep the energy consumption low and to ensure digital signal integrity throughout the system. The smallest possible system, one light fitting and a controller consunes a line current of maximum 2 mA for the digital dimmable ballast and the current required by the control equipment. Thus the power consumed is small. Since in practice the impedance of different DALI units are not identical, the selection of the correct system power supply not necessarily straight forward. Good practice is to allow sufficient margins for the supply current. This will guarantee reliable system functionality under different conditions and also allow the flexibility for possible system expansion at a later date. On the other hand, selecting an oversized power supply may cause extra distortion control signals Power supplies, which have so called dynamic current limitation, will be suitable for use in almost every size of system.

Requirements for DALI power supplies.
The DALI power supply must limit the supply current to max. 250 mA under all circumstances. In practical installations the current is good to limit to a lower level in order to maintain the flexibility of changing the layout and increasing the system at later stages. If the limit is exceeded instability and starting problems may occure in the system. Since the DALI signal varies between 0V and 16V the polarity is important to maintain also with power supply. There is no limitation to having several power supplies on the same DALI control line as long as the current limit is not exceeded and the supply polarity is taken into account.

DALI - LIGHTING WITH INTELLIGENCE
(DALI - Digital Addressable Lighting Interface)
The new method involves using DALI-protocol-based technology (i.e. digital control signals) to control electronic ballasts, controllers and sensors belonging to the system. Each system component has its own device-specific address, and this makes it possible to implement individual device control.

History of the DALI protocol
Research work connected to the DALI project began midway through the 1990s. However, the development of commercial applications got under way a little later, in the summer of 1998. At that time, DALI went under the name DBI (Digital Ballast Interface). An interface device (or ballast) is an electronic inductor enabling control of fluorescent lamps. In addition to the work done at Helvar, the DALI standard has been the subject of R&D by other European ballast manufacturers such as Hüco, Philips, Osram, Tridonic, Trilux and Vossloh-Schwabe. The DALI standard will be added to the European electronic ballast standard “EN60929 Annex E”. Different manufacturers´ products can be interconnected provided that the manufacturers adhere to the DALI standard. This standard embodies addressability, i.e. ballasts can be controlled individually when necessary. To date, ballasts connected to an analogue 1-10 VDC low-voltage control bus have been subject to simultaneous control. Another advantage enabled by the DALI standard is communicating the status of ballasts back to the control unit. This is especially useful in extensive installations where the light fixtures are widely distributed. The execution of commands compliant with the DALI standard and obtaining the status data presuppose intelligence on part of the ballast. This is provided by mounting a microprocessor within the ballast; the microprocessor also carries out other control tasks. The first products based on the DALI technology were commercially available from the end of 1999.

DIGITAL CONTROL
The word “digital” is a term which has become familiar to us all in the course of this decade in connection with the control technology built into domestic appliances as well as into industrial processes. Now, digital control is becoming increasingly common in the lighting industry under a new concept bearing the name DALI.

DALI MESSAGE STRUCTURE
DALI messages comply with the Bi-Phase, or Manchester, coding in which the bit values “1″ and “0″ are presented as two different voltage levels so that the change-over from the logic level “UNTRUE” to “TRUE” corresponds to bit value “1″, and the change-over from the logic level “TRUE” to “UNTRUE” corresponds to the bit value “0″. The coding includes error detection and enables power supply to the control units also when there are no messages being transmitted or when the same bit value is repeated several times in succession. The bus´s forward frame (from the control unit to the ballast) is comprised of 1 START bit, 8 address bits, 8 data/command bits, and 2 STOP bits. The backward frame (from the ballast to the control unit) is comprised of 1 START bit, 8 data bits and 2 STOP bits. The baud rate is 2400.

DALI messages consist of an address part and a command part. The address part determines which DALI module the message is intended for. All the modules execute commands with “broadcast” addresses. Sixty-four unique addresses are available plus sixteen group addresses. A particular module can belong to more than one group at the one time.
The light level is defined in DALI messages using an 8-bit number. The value “0″ (zero) means that the lamp is not lit. The DALI standard determines the light levels so that they comply with the logarithmic regulation curve in which case the human eye observes that the light changes in a linear fashion. All DALI ballasts and controllers adhere to the same logarithmic curve irrespective of their absolute minimum level. The DALI standard determines the light levels over a range of 0.1% to 100%. Level 1 in the DALI standard corresponds to a light level of 0.1%.

TYPICAL DALI MESSAGES
Go to light level xx.
Go to minimum level.
Set value xx as regulation speed.
Go to level compliant with situation xx.
Turn lamp off.
Query: What light level are you on?
Query: What is your status ?

FROM ANALOGUE TO DIGITAL
The idea concerning the DALI protocol emerged when the leading manufacturers of ballasts for fluorescent lamps collaborated in the development of a protocol with the leading principle of bringing the advantages of digital control to be within the reach of as many users as possible. Furthermore, the purpose was to support the idea of “open architecture” so that any manufacturer´s devices could be interconnected in a system. The precondition to this was for the manufacturers to commit themselves to the DALI standard.

In addition to control, the digital protocol enables feedback information to be obtained from the lighting fixture as to its adjustment level and the condition of the lamp and its ballast.

Examples of typical applications for the new system are office and conference facilities, classrooms and facilities requiring flexibility in lighting adjustment. The lighting-control segment based on DALI technology consists of maximum 64 individual addresses which are interconnected by a paired cable. DALI technology enables cost-effective implementation of lighting control of both smart individual lighting fixtures as well as of numerous segments connected to the automation bus of a building.

ADVANTAGES IN INSTALLATION AND USE
To understand the function of a simple light switch is something that everybody can do. It turns on and off the light. To get a more complicated lighting control system to be easy to control, without problem for the user, is now possible. The challenge facing new control systems is for them to be able to offer a flexible and easy-to-use means of lighting control with respect to the demands of both users as well as the facility. All the components of the DIGIDIM system can be controlled either independently or in a group. This being the case, DIGIDIM enables the flexible use of lighting control to different situations. The creation of variable lighting situations is especially important in conference rooms, offices, restaurants and other such multiple-use facilities. A soft transition from one lighting situation to another is possible thanks to programmable adjustment speeds. The system can be flexibly reprogrammed as the need arises, e.g. when using partitions. Also, the system enables the control of different combinations of light sources, e.g. ordinary fluorescent lamps, miniature fluorescent lights, discharge lamps, incandescent lamps and halogen lamps.

In their simplest form, installation and application can be implemented using the devices by connecting only the mains supply cable to the lighting fixtures and the control cables between the various components. DIGIDIM pushbuttons include lighting control levels compliant with the basic programming, and thus the system is ready to be used once the cabling has been completed. Modifications in the lighting levels are easy to perform directly via a pushbutton by adjusting the lighting to a suitable level with the Up/Down buttons and by finally saving the desired lighting level to one of the lighting-level recall pushbuttons. When programming more extensive systems, a PC-based installation program can be used for creating different lighting groups.

USER CONVENIENCE AND COST EFFICIENCY
In northern parts of Europe, like Scandinavia, the use of cooling air condition systems can be needed to use more then 6 months a year. Part off that energy is for cooling the heath dissipation from luminaries. In buildings provided with gravity-based ventilation, lighting can account for as much as 40% of the energy costs, and in buildings with air conditioning, lighting and ventilation can constitute an even more significant part of the energy costs. Using constant light control and presence detection can ver much reduce these costs. If we take an example: In an office with standard luminaries, the energy consumption for light can be reduced with up to 80% if a solution with new T5 tubes, constant light and presence detection is installed. Also, constant light control adds to the user convenience of the persons in the facility because the system always, and automatically, executes the lighting level desired by the user. Poor lighting has a detrimental effect on people, and it can ultimately cause eyestrain and headaches.

Further information:
AG-DALI: http://www.ag-dali.org

Performance Standard: IEC 929 / EN60929 Annex E (Control Interface for Controllable Ballasts)

Summary:
DALI - Digital Addressable Lighting Interface - brings the benefits of a new industry standard to lighting-control systems. It has been developed specifically with optimum lighting control in mind, both in local room control applications and when interfacing with building management systems. The DALI protocol, based are a draft amendment to IEC 929, has been adopted as a new standard by major ballast manufacturers such as Helvar, Hüco, Philips, Osram, Tridonic, Trilux and Vossloh-Schwabe. As a dedicated communication interface for the control of lighting systems, DALI enables sophisticated lighting control while greatly increasing flexibility and reducing installation costs.

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