Why Digital?

A Case for Digital Controls

The Best of Both Worlds – Aesthetic Scenes & Energy Management

vart1Digital Building Management Systems (BAS) have existed throughout the United States since the advent of Direct Digital Controls in the early 1990’s.  Around the same time, the Digital Addressable Lighting Interface (DALI) standard for digital lighting controls became a popular dimming communication protocol in Europe (Europe’s Standard 60929) and quickly spread to most other parts of the globe.  DALI has been a NEMA Standard (243-2004) in the US since 2004.

Digital control of lighting offers- for the first time- a method of control that is simple to understand and design as well as easy and affordable to install.  Through the use of DALI, the aesthetic requirements of space occupants and the benefits of an energy management system can be integrated into one comprehensive system.  The needs of both space occupants and operational managers can now be simultaneously satisfied, as users complete control over their lighting environment ensures they will use only the amount of artificial lighting needed – and that very control provides the energy savings sought by the building’s management.

 The benefits for DALI’s digital control of lighting include:

It is essential that a modern lighting control system keep up with the ever changing landscape of light sources.  DALI is a prime example of this rule, having its roots firmly entrenched in Europe where new sources debut years before they appear in the US.  Standard DALI enabled devices allow the control of numerous sources including Incandescent, Low Voltage, Fluorescent, HID and LED each in a wide variety of wattage ranges and container styles (F-can, Downlight, et cetera).

Developed as an international, non-proprietary protocol, DALI is manufactured by the main producers of transformers, ballasts and drivers throughout the world.  US manufacturers include Philips/Advance, Osram/Sylvania, Universal Lighting Technologies, and Tridonic.  These manufacturers collectively produce millions of lighting control devices which keeps them at the forefront of electronic ballast and driver technology.  The number of manufacturers keeps costs at a minimum due to the competition for market share.

Each ballast and driver is provided with a memory location for its system defined address – assigned during commissioning.  Using these addresses the digital control system creates a “lighting network” similar to a computer network.  Individualized directives can then be directed to individual fixtures or digitally created groups, allowing the designer of the lighting system, or the space occupants, the ability to create assignable scenes – much like those used in theater.

Through the use of scenes, space designers and end users can adjust the output of each fixture individually to direct the right amount of light exactly where it is needed.  Scenes can be stored in system memory, allowing it to be recalled as needed.  This allows for spaces with multiple uses, such as conference rooms (which host meetings, presentations, video conferences, etc.), to recall a predefined lighting scene appropriate for the space’s current use.

For a number of years we have been hearing about the benefits of “Smart Ballasts” – fluorescent power transformers capable of fully independent fixture control.  Each ballast or driver contains an internal processor and memory programmed with a unique address.  This unique address allows each ballast or driver to operate independently within a digital lighting control network using the DALI protocol.

DALI “Smart” ballasts are manufactured by most major ballast manufacturers and incorporate all the features of their best ballasts (s/n ration, power factor, etc.) together with full-range, stepless dimming and independent switching (each ballast can be independently turned on or off).

While full-range dimming control has been available with 0-10v ballasts for some time, the control circuit providing the 0-10v signal was shared with several fixtures – all operating together in unison.  Independently addressed DALI “Smart” ballasts allow for each fixture to respond independently to changing environmental situations and user requirements.

Most importantly, though, is the independent switching offered by DALI ballasts.  Not only does this allow each fixture to be switched off independently as needed, it also allows power circuiting to be delivered in the most efficient manner, independent of grouping/zoning or controls, as fixtures are now turned off within each fixture at the direction of the communication system.  This eliminates the need for contactor or relay panels which are required by 0-10v systems – as their analog ballasts only dim, and cannot turn the lamps on or off.

Each digital ballast or driver is enhanced with independent microprocessor and storage capabilities, internally programmed to provide a full range of control functions at the fixture level – rather than depending on a smart “Comand Center.”  DALI ballasts enable system designers to store individual attributes to each fixture: i.e., identification of power outage, assignment of fixture operation under emergency power, determination of fixture operation after return of normal power, operational maximum operating level, operational minimum operating level, 16 scene assignments, and fade rate between called scenes.  Characteristics which were previously not available using analog technology except with the most complex systems, and only assigned on a circuit by circuit basis, are now assignable on a fixture by fixture basis.  And where previous systems required technicians to make any desired changes, “Smart” ballasts can be re-commissioned by the system through the digital bus.

Digital lighting control systems allows for true two-way communication between each “Smart” digital ballast or driver and the software management system.  Not only can each ballast respond to system commands, but individual ballasts are capable of notifying the system control software of current operation state, lamp or ballast outages, as well as identifying energy usage at the fixture level.  Facilities and Maintenance staffs for the first time have an allay in maintaining the lighting system to its fullest capability.  Rather than having to walk around looking for problems, and then guessing at their cause, daily or weekly reports can be generated identifying each specific issue, allowing maintenance staff to respond initially with the right solution.
Digital lighting systems utilize “Smart” ballasts or drivers, each having provisions to receive two completely separate groups of wiring: Power circuit wiring (power, neutral and ground) and Control circuit wiring (two low voltage wires).  In addition, each DALI ballast is equipped with an internal switch, capable of independent on/off control of its source(s).

While both power and control wiring can be delivered in Class 1 (power and control wiring run in common conduit) or Class 2 (power and control run separately) methods, as defined by the NEC, the ability to ignore control when designing power wiring circuiting allows for increased efficiencies in wire, conduit and switch gear.

Power Wiring

In digital system design, power wiring is distributed in the most efficient manner possible given national and local requirements – resulting in reduced switch gear sizing.  This is only possible in digital systems where the switching function is localized in each ballast or driver.  Analog 0-10v systems can dim, but still require power wiring to be designed to allow for zone switching.  Additionally, as power wiring distribution ignores control schemes, gone are the switch legs and 3-way switch wiring travelers in many of the simplest analog power wiring designs.

This may mean that fixtures within a given space can be fed from multiple electrical circuits.  This is not an issue as fixture control is not power circuit dependent, but switching and dimming is controlled through the DALI communications circuiting.  As on/off switching is provided in each ballast or driver, every device receives constant power without the power interruption equipment (contactor panels, etc.) typically required in analog systems.

Control Wiring

Digital systems using the DALI protocol are structured using independent Control Circuits, each capable of commanding a maximum of 64 addresses for ballasts and another 64 addresses for control devices (switches, sensors, etc.).  Each digital control circuit is comprised of a two-wire bus (or loop) distributed to each ballast or driver, switch, sensor, and DALI enabled device using a topology (star, daisy-chain, etc.) most beneficial to the specific project.  These digital communication circuits do not require special cabling, typically utilizing shielded wire between 16ga and 12ga.  One point of clarification: DALI communication buses are terminated at its end(s), which can become confusing as, in DALI terminology, communication buses are typically referred to as “Loops”.

Unlike analog technology, digital systems control devices are polarity insensitive – meaning that positive and negative signals are optocoupled within each device, eliminating the chance of miswiring in the field.  In addition, each control zone’s wiring is distributed identically throughout the lighting control system, with each ballast, switch and sensor receiving an identical two-wire connection.  This eliminates the “special cases” common in analog systems.

Power & Control Wiring Together – in the Same Conduit

But possibly the most important difference between analog and digital DALI control wiring is the integration of control wiring within the power conduit.  Analog systems require communications wiring to be run independent of power due to the influence of EMF on control signals – a substantial increase in both material and labor costs.  Digital DALI wiring is not susceptible to typical power wiring EMF, and thus can be integrated into power circuit conduit (per NEC Article 300.3) without issue provided the insulation rating of the communications wire is the same or greater than the highest rated power wire in a common conduit.  If desired, DALI wiring can be run separately (Class 2) in conduit or plenum rated cable depending on local codes.

Traditional analog controls created groups based on 0-10v control wiring, with each groups home run brought back to a master dimming cabinet.  Each group (or Zone) of fixtures is controlled together, with all fixtures dimming at the same rate to identical light levels.  As analog controls provide only full range dimming on a zone by zone basis, on/off control requires a separate contactor or relay.

Individual fixtures can only be controlled by one 0-10v group or zone control, limiting lighting system control flexibility in larger control zones.  In multi-use spaces such as conference rooms and multipurpose spaces, it is desirable to have fixtures belong to more than one group, or to have individual fixtures achieve a number of different light levels depending on the scene called.  To achieve maximum flexibility, analog groups or zones must be reduced in size so only a small number of devices are controlled in each wired circuit.  As a lighting system’s control groups are reduced in size to allow for lighting system flexibility (to enhance the use of each space), wiring complexity and system cost grow dramatically.  If taken to its logical intent, each fixture would have to be individually controllable through its own independent control wiring circuit – a scenario in an analog system which would be extremely difficult to design, circuit and afford.

Example 1:  Daylight Harvesting in a Classroom

Academic studies have determined that to maximize student attention spans, changes in activities should be accompanied by an adjustment in the lighting system.  Lighting levels are varied from the front to the back of the classroom to accommodate various activities: i.e.: Video presentations require the fixtures casting light onto the screen be turned off, and lights at the front of the room are lowered to a minimum light level.  Subsequent rows of lights are set to slightly higher levels to the back where light levels attain approximately 10fc.  This provides enough light to keep the students awake, and allows the teachers visibility of all students throughout the room.

Whiteboard presentations require attention focused toward the front of the room.  Teachers often want the reverse of the video presentation, where the lights are fully illuminated at the front of the room (illumination the white board and teacher) and subsequent rows toward the back of the room; the row farthest from the whiteboard is diminished to 50% of the levels at the front of the room.

In either case above, natural daylight illuminating the room through windows along one long side of the classroom (perpendicular to the front of the room) can be utilized to reduce the need for artificial light – reducing energy costs and a facilities carbon footprint.  Modern lighting systems must be able to capture the occurrence and intensity of natural daylight and diminish the lighting system to minimize the energy used by the lighting system while provide the needed light for each task or activity.

The Analog Approach

While the concept of a lighting system allowing architectural (user) concerns to coexist with energy management (operations) operations is intuitively obvious, the design of such a system in an analog design is quite complicated and extremely expensive.  What is needed is for every fixture to live in two groups:  Rows of fixtures parallel to the board must operate together (to provide varied light levels as detailed above) and rows parallel to the windows must be diminished together (to accomplish daylight harvesting).

Such a scenario will require each fixture in the row nearest the front of the room and each fixture in the row nearest the windows to be in their own group or zone – each zone or group containing only one fixture.  An optimum system would have all fixtures throughout the room each in their own separate group.  The complexity of design and installation together with the dramatic affect to system cost prohibits such circuiting from being commonplace.

And then there is Digital Lighting Control!

Digital lighting systems, by their very nature, lend themselves to sophisticated systems such as these.

Individually Addressable Fixtures

To begin with, each fixture is assigned a unique address (much like computer MAC addresses) at time of commissioning, creating a lighting network of fixtures, switches and sensors similar to computer networks (with their interconnected groups of computers, printers, scanners, etc.).  This allows system designers and users to control fixtures individually or in software defined groups.  As all groups are software assignable, changes to the use of each space or changes to the spaces themselves (moving of walls, etc.) do not require rewiring – only regrouping via user software.

Scene Selection

In operation, each space can have up to 16 scenes (such as whiteboard presentation of video presentation as detailed above) to accommodate the various uses of the space.  This allows users to focus the right amount of light only where needed, minimizing energy usage.  To define this multi-scene control intent to the contractors, system designers no long have to create complex control wiring schematics.  Instead they prepare text based “Sequence of Operations” detailing how the system is to operate for each scene and the interaction of any environmental elements: such as Daylight Harvesting.

Easy Integration of Sensors and Switches

Sensors and switches can be integrated in the most appropriate locations, providing user control stations where needed and environmental controls in the most optimum locations.  Each control device is attached to the same control wiring (bus) that connects ballasts and drivers.  In this way all devices are integrated into one simple two-wire control network allowing each element to communicate with any other.

Daylight harvesting activities can be directed to each fixture individually, allowing each fixture in the system to provide different light levels to achieve the lighting goals of the space while harvesting the maximum benefit from the natural (free) daylight.

Simple and Efficient Wiring

And the best part:  rather than having to create a multitude of zones or groups within a space to provide the granularity of control, each with its own power and communication wiring, the digital system allow electrical designers or contractors to design a power system that is most efficient for the building, and deliver one uniform control circuit of any wiring topology (daisychain, star, etc.) to a room or series of rooms.  Wiring design and installation become simple, as the complexity of control is handled using the ballast’s or driver’s individual addresses – simple and efficient!

Limited to 64 ballasts and 64 devices (such as switches and sensors)

Does not provide universal protocols for all communication:

Motion and Photo Sensors

Integration with 3rd party systems such as BAS, Fire Alarm, etc.

Back to Top