Digital Addressable Lighting Interface
|This article relies too much on references to primary sources. (February 2012)|
IEC 60929 and IEC 62386 are technical standards for network-based systems that control lighting in building automation. They were established as a successor for 0-10 V lighting control systems, and as an open standard alternative to Digital Signal Interface (DSI), on which it is based. IEC 60929 is the first version of the standard and will be withdrawn by 23 June 2014. Members of the AG DALI are allowed to use the Digital Addressable Lighting Interface (DALI) trademark on devices that are compliant with the current standard. Non AG DALI members can apply for a fee bearing license. It was found and generated by Philips lighting in 1984.
DALI (Digital Addressable Lighting Interface) is a data protocol and transport mechanism that was jointly developed and specified by several manufacturers of lighting equipment. The common platform of DALI enables equipment from different manufacturers to be connected together.
DALI network consists of a controller and one or more lighting devices (e.g., electrical ballasts and dimmers) that have DALI interfaces. The controller can monitor and control each light by means of a bi-directional data exchange. The DALI protocol permits devices to be individually addressed and it also incorporates Group and Scene broadcast messages to simultaneously address multiple devices (e.g., "Group 1 goto 100%" or "Recall Scene 1").
Each lighting device is assigned a unique static address in the numeric range 0 to 63, making possible up to 64 devices in a standalone system. Alternatively, DALI can be used as a subsystem via DALI gateways to address more than 64 devices. Data is transferred between controller and devices by means of an asynchronous, half-duplex, serial protocol over a two-wire bus, with a fixed data transfer rate of 1200 bit/s.
DALI requires a single pair of wires to form the bus for communication to all devices on a single DALI network. The network can be arranged in a bus or star topology, or a combination of these. The DALI System is not classified as SELV (Separated Extra Low Voltage) and therefore may be run next to the mains cables or within a multi-core cable that includes mains power. The DALI data is transmitted using manchester encoding and has a high signal to noise ratio which enables reliable communications in the presence of a large amount of electrical noise. DALI employs a diode bridge in the interface circuitry so that devices can be wired without regard for polarity. Signal level are defined as 0±4.5 V for "0" and 16±6.5 V for "1". Central interface power maximum is 250 mA and 2 mA per unit. The network cable is required to be mains-rated, with 600 V isolation and at least a 1 mm cross-section, with a maximum drop of 2 volts along the cable (max 300 m). Signal interface is galvanically separated and doesn't need any termination resistors. DALI is a step on from the DSI protocol, which is used by HF fluorescent ballasts. One of the main advantages that DALI has over earlier systems is that each device on a segment of data cable can be separately addressed, as DSI and 1-10V devices are not separately addressable and can only be controlled as a group. The net result is that to achieve similar control functionally, DALI requires less complex (and therefore less expensive) wiring topology than DSI or 1-10V devices.
DALI devices include fluorescent HF ballasts, low voltage transformers, PE cells, motion detectors, wall switches and gateways to other protocols. There can be up to 64 DALI devices on a single DALI network. Sites requiring more than 64 devices are implemented by having multiple separate DALI networks, each with up to 64 devices. These separate networks are then linked together with DALI gateways and a data backbone running a high level protocol, such as Dynalite’s DyNet.
Earlier generations of DALI devices stored configuration data in EEPROM, which was problematic due to the limited number of write cycles supported by EEPROMs. In current generations of DALI devices, RAM is used in preference to EEPROM during normal operation, which significantly reduces the number of EEPROM writes and thus extends their lifetimes. This use of RAM, however, is patented and therefore mandates payment of a license fee.[to whom?]
DALI requires 2 wires to devices, in addition to mains cables if required. These wires are not polarity dependant which makes it simple to install. These wires are at ELV (Extra Low Voltage) potential and are looped to all devices. Some devices, such as HF ballasts are mains powered, and only have functional isolation between the mains and the DALI control. This means that even though the DALI control cable operates at ELV potential, it must be treated as if it were at mains potential. A DALI network requires a 24V DC 250 mA power supply to operate. This voltage appears on the data cables and can be used to supply power to peripherals that require it, such as motion detectors. A separate power supply can be used, some manufacturers have DALI gateways with an integral power supply.
A DALI device, such as a HF fluorescent ballast, can be controlled individually via it's short address. In addition to this method of control, DALI devices can be arranged into groups in which all devices of the same Group can interact with each other. For example, a room with 4 ballasts can be changed from off to on in two common ways:
Method 1 – Using the Short Address, eg sending the following DALI messages:
- DALI Short Address 1 go to 100%
- DALI Short Address 2 go to 100%
- DALI Short Address 3 go to 100%
- DALI Short Address 4 go to 100%
This method has the advantage of not relying on the limited number of scenes available in each ballast, or having programmed each ballast with the required group numbers and scene information. The fade rate of the transition can be chosen on the fly. This method can have an undesirable side effect called "Mexican Wave" when a single large room such as an auditorium contains many ballasts, due to network latency of the comparatively slow 2400 baud rate of DALI. For example, a transition from all on to all off may result in a visible delay between the first and last ballasts switching off. This issue is normally not a problem in rooms with smaller numbers of ballasts.
Method 2 – Using the DALI Group previously defined for the ballasts in the room, eg:
- DALI Group address 1 go to 100%
This method has the advantage of being immune to the “Mexican Wave” effect as described above. This method has the disadvantage of requiring each ballast to be programmed with the required group numbers and scene information, and has a fixed fade rate which is pre set at the time of commissioning.
The DALI protocol provides 256 levels of brightness between off and 100%, which is translated to a ballast power level via a logarithmic dimming curve. This curve gives larger increments in brightness at high dim levels and smaller increments at low dim levels. This is an attempt to have a dimming curve which appears linear to the human eye. Sometimes issues arise when different fixtures are used together, such as DALI fluorescent ballasts, DALI ELV Incandescent transformers and phase control dimmed fixtures. When different fixtures are operated together it is often apparent to the eye that the dimming curves do not match, especially at lower levels, due to the lower end distribution of the DALI dimming curve.
A wireless extension to DALI is available that enables DALI networks to communicate via wireless, radio frequency communication.
- "Communication in building automation". Siemens Building Technologies. Siemens Building Technologies. 2013. Retrieved 12 July 2013.
- dali-ag.org "Digital Addressable Lighting Interface". DALI. DALI AG, Activity Group, ZVEI-Division Luminaires. September 2001. Retrieved 12 July 2013.
- "Wireless extension for DALI". Virtual Extension. Virtual Extension. 2014. Retrieved 3 August 2014.