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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 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.

What DALI can do for you
What DALI will NOT do
Maintenance considerations
DALI specifications in a nutshell
DALI Transport
Dimmable HF Ballast controll comparison
DALI devices power consumption
DALI addressing
DALI grouping
Dimming Curve
DDBC320-DALI controller
DDBC320-DALI setup and operation

What DALI can do for you

• Facilitate the easy integration of equipment from different vendors
• Reduce installation costs
• Offer a finer granularity of control for a given price

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What DALI will NOT do

• Remove the need for a data cable to connect fixtures
• Lower commissioning & programming times
• Save the maximum possible amount of energy (unless extra equipment is used as described below)
• Remove the need for a backbone running a high level protocol in larger sites

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Maintenance Considerations

As a site becomes older a task maintenance personnel are often required to perform is the replacement of failed ballasts. This is relatively simple if the site uses standard, DSI or 1-10V ballasts but is not the case with DALI ballasts, as unlike the other ballast technologies a DALI ballast has a unique address programmed into it. A replacement ballast must be set to the same address as the original ballast, unfortunately all DALI ballasts currently on the market only have their addresses settable and viewable with special equipment, requiring maintenance staff to have access to this equipment to set the address in the new ballast and "as installed" documentation to determine the address of the failed ballast. This process may add to the cost of replacing failed ballasts.

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DALI Specifications in a nutshell

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DALI Transport

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. When choosing a DALI cable, use a mains rated cable with conductor sizes as per the chart below:

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Dimmable HF ballast Control Comparison

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DALI Devices Power Consumption

DALI devices consume power to operate. DALI ballasts have the capability of fully extinguishing the lamps with mains power still applied to the ballast. This can simplify the mains wiring of some implementations as there is no requirement to switch off the mains when the lights are turned off. Careful consideration should be given before deciding to leave the mains permanently applied to the ballasts as the control electronics in each ballast continues to draw energy even when the lamps are extinguished, with some brands of ballast this "off state" power consumption can be significantly high to become an energy management and wiring issue, particularly on sites with large numbers of ballasts.

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DALI Addressing

DALI devices have two addresses:

Short address - This is a 6 bit number, which allows a maximum of 64 devices on a DALI network. Each DALI device must have a unique address, which is frequently used for normal control of the DALI system. A short address conflict is when two or more DALI devices have the same short address. In this situation device(s) that have the same short address must be re configured to have a unique address.

Long Address - this is a 24 bit value that is primarily used for resolving short address conflicts at the time of commissioning. The long address is such a large number that the chances of two in a group of up to of 64 devices having the same long address is small, but it can happen. In this case there is a "Randomise Long Address" command that is used to resolve the long address conflict.

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DALI Grouping

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.

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Dimming Curve

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.

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DALI DDBC320-DALI Controller

The DDBC320-DALI is a self contained DALI controller that can be used as a gateway to link multiple DALI networks together. It has an inbuilt DALI network power supply, and a relay to automatically switch off power to ballasts when all are at 0%. It can operate in two modes:
• Group & scene mapping mode - Limited control functionality, no "Mexican Wave" effect in large rooms.
• Short address mode - Maximum control functionality, large rooms may be prone to the "Mexican Wave".

Mode Comparison Table:

* 65535 DBC120-DALI devices on a DyNet2 network, each controlling 192 DALI devices

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DDBC320-DALI Setup and Operation

The device appears on the Dynalite network as a 192 channel load controller, and is commissioned like any other Dynalite load controller using DLight. Once placed in setup mode it will automatically find and configure DALI devices connected to it, and keeps information on them, so if a single DALI device fails and is replaced only the replaced unit will require reprogramming, and the existing devices will retain their original settings, even if all DALI long and short addresses are re allocated.

The DDBC320-DALI supports diagnostic functions such as ballast lamp arc power and lamp failure, provided the ballasts used also support the desired function. More info on DALI controllers.

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