Bright Ideas in Lighting Control

Bright Ideas in Lighting Control

Manufacturers are developing new lighting control devices and systems at such a rapid pace, few new projects will incorporate the same components. The most prevalent modern lighting control strategies can be divided into four categories: occupancy-based, schedule-based, light-level control, and load shedding.

Today, when even the smallest capital expense requires approval from the top, electricity is an easy place to cut costs. New lighting control technologies help you light the workplace appropriately and save money along the way.

Lighting control has come a long way from the early days of the simple toggle switch. Now lighting designers have devices like passive infrared detectors, solid-state contactors, ultrasonic devices, and photosensitive controls at their disposal. In fact, manufacturers are developing new lighting control devices and systems at such a rapid pace, few new projects will incorporate the same components.

The keys to customer satisfaction are understanding your clients' needs and using the right devices as part of sophisticated lighting control strategies and control systems within their facilities. You must understand what type of visual tasks will be performed in the facility, what the electricity rate is at various times of the day, and what controls are the most suitable for each room. Only then will you continue to stay one step ahead of your competition.

Control strategies.

The most prevalent modern lighting control strategies can be divided into four categories: occupancy-based, schedule-based, light-level control, and load shedding.

Occupancy-based control involves switching lighting on and off in response to the presence of people in a particular space. A schedule-based system activates lighting at pre-set time intervals that can extend to minutes or hours. Schedule-based systems include astronomical control, which is dictated by daytime sunlight levels. Light-level control switches between the following three types of control to adjust the light output in response to defined objectives:

  • Daylighting allows natural light that enters a building or structure to supplement electric lighting systems.

  • Tuning allows the adjustment of light levels to match the different activities conducted in a space.

  • Lumen maintenance allows an even level of illumination throughout the useful life of the lamps in a lighting system. The lighting system is set to a predetermined dimming level when the lamps are initially installed, and the light level is increased incrementally as the lumen output of the lamps decreases over time.

Load shedding control systems permit a reduction in a facility's total lighting load to achieve a reduction in power demand, usually in the middle of the day.

Control mediums.

Lighting system control signals can be distributed throughout a facility via a low-voltage communications bus or a power-line carrier system.

A low-voltage communications bus uses a set of twisted-pair copper conductors to carry data to and from control panels and other equipment. The bus control system simplifies wiring, which means that individual, group, or pattern switching of lighting can be easily changed or added.

A power line carrier system consists of transmitters and receivers that use the building's AC power conductors as a communications pathway. The transmitter accepts a control signal, converts the signal into a coded digital form, and using a frequency from 25 kHz to 250 kHz, places the signal onto the AC power conductors to be picked up by the receiver.

A power line carrier system can be applied in large facilities with several control points, and it can be an economical choice for existing buildings where the cost of installing new control wiring is prohibitive. Care must be taken in designing and installing the system because transient voltages, or noise, on the branch and feeder circuit conductors can adversely affect the performance of the system.

Equipment review.

Lighting control devices are classified as on/off devices or power level setting control devices. Those that provide on/off switching control include:

A wall switch can control a branch circuit directly or a contactor or relay-operating coil to achieve multiple-circuit control in a single action. In a space where a number of lighting circuits are installed, it's standard practice to group a number of wall switches in a single location, such as a doorway. This will permit selective use of specific lighting loads in the space and allow different light levels to be established.

Locations with more than one means of entering or leaving an area, such as a passageway or corridor, commonly call for 3- and 4-way switches. A number of NEC rules must be observed in this case, such as the requirements on the identification of “travelers.”

A circuit breaker in lighting and appliance panelboards is sometimes used to provide on/off control of a lighting branch circuit. However, only a device rated for switching duty should be specified for such an application to ensure long service life. A solenoid-type breaker operating through a Class 2 control circuit is another option. Remote indication of circuit breaker status can be provided at a central monitoring location, and the solenoid breakers may also be incorporated into a building's total automation system.

A lighting contactor can also operate lighting circuits from a remote location. Typically rated from 20A to 400A, these devices can be electromagnetic or solid-state in construction and mechanically or magnetically held.

Although an electromagnetic motor starter contactor looks similar to a lighting contactor, it shouldn't be used for lighting applications. Certain lighting loads can have very high inrush currents, with characteristics much different than a lighting load.

Contact bounce is another phenomenon to consider when applying an electromagnetic contactor. When a contactor coil is energized, the movable contacts strike the stationary contacts with considerable force. Even though the distance involved is relatively small, the movable contacts actually bounce off the stationary contacts at least once before firmly seating themselves.

The inrush current of tungsten lamps can reach as high as 18 times normal operating current for a very short time period. This inrush period is coincident with the contact bounce. During this period an arc hot enough to melt silver strikes across the contacts. Other types of lamps and ballasts have different characteristics that could also damage a non-lighting-load contactor. Thus, a lighting designer should confirm a contactor's rating and the lighting loads being served.

A low-voltage switching control system consists of compact switches, step-down transformers, and latching relays. Additional components are available for extending the system's versatility and convenience.

Since a pair of No. 22- or No. 24-gauge conductors are normally used to connect the components, the system is fairly easy to install in new installations or remodeling projects. The control wiring is classified as a remote-control and signaling circuit, and many jurisdictions permit running these cables in above-ceiling spaces and risers without the use of conduit.

Low-voltage switching uses a latching relay to provide on/off control of a branch circuit or individual luminaires. The relay contacts usually have a 20A filament load at a 125VAC rating. The contacts are mechanically latching, requiring only a momentary 24V, rectified AC switch-circuit pulse to open or close the line voltage branch circuit contacts. Power for relay operation is often provided by a 40VA step-down transformer, which can serve as many as 15 relays. A relay body can be mounted in a .5-in knockout of a wiring box or a barrier strip in a relay panelboard.

A relay typically has three leads to provide the circuit path through the solenoid for latching or unlatching the contacts. Another type has an internally energized contact for a pilot light and uses four leads. A third version has an isolated internally energized pilot contact and uses five leads.

These relays can be incorporated into any level of automated control yet still allow each relay to be directly controlled by a wall switch, an occupancy sensor, or a combination of both.

Architectural lighting control systems have evolved over the years to provide a host of operational features for automatically creating lighting scenes in defined areas or rooms of a facility. Also called scene lighting controls, these units allow any group of lighting fixtures, including multiple luminaires energized from different phases of the power system, to be activated at a user-programmed brightness level. The ability to simultaneously control the brightness levels of numerous luminaires allows illumination levels to correspond to the tasks and moods of the occupants. Typical applications include restaurants, conference rooms, training rooms, houses of worship, and living and entertaining areas in home residences. The newest digital styles of architectural lighting control systems are most popular because they're easy to expand.

Remote/dimming control allows an individual office occupant to switch lights on or off to reduce the illumination level. The user can match the light level to a specific work task, making the controls useful in implementing task tuning. Control is accomplished through several methods, including commands sent from a PC connected to a local area network (LAN), a telephone keypad connected to the building's central controller, or a handheld infrared (IR) or radio frequency (RF) controller operated by the office occupant. In the last example, the control signals are sent to a receiver mounted in the ceiling or within the overhead luminaire. Local control methods stand to become more popular with the increased application of PDAs, wireless phones, and similar devices.

Automatic switching controls.

A number of products are available for automatically controlling the light level within a space.

An occupancy sensor activates the lighting circuit only when someone is in the space. The light will remain on for a set amount of time after the person is no longer detected in the room. Time delay settings are adjustable, usually from 30 sec to 12 min.

The three types of occupancy sensors are passive infrared, ultrasonic, and a dual-technology device that uses both passive infrared and ultrasonic technology.

A passive infrared (PIR) device senses occupancy by detecting the difference between heat emitted from the human body in motion and the background space. Relying on a clear line of sight, passive infrared sensors use Fresnel lenses to create a defined pattern of coverage in both the horizontal and vertical planes. The latest technology ensures higher sensitivity to minor motion without the potential for false activation.

PIR devices are available in a wall-switch model (in place of a standard snap-switch at a doorway) or a ceiling-mounted unit. In addition, ceiling-mounted PIR units offer a number of features, including ambient light override and an automatic dual-mode operation that adjusts to either economy or high-sensitivity mode based on actual occupancy patterns for maximum energy savings. A built-in Circadian Calendar provides a four-week learning period during which the sensor monitors occupancy to establish trends that serve as the basis for automatic operation. During peak occupancy periods the sensor remains in high-sensitivity mode, and during low occupancy periods it switches to economy mode.

Wall-switch PIR devices also offer a number of useful features, including a provision for automatic switching of two separate banks of incandescent, fluorescent, or low-voltage lighting from a single unit; dual pushbuttons for manual operation of each load; and automatic “walk-through” sensing, which shuts off lights within 2.5 min after momentary occupancy.

Ultrasonic sensors transmit and receive low-intensity sound waves at a frequency of about 25 kHz to 40 kHz, which is inaudible to the human ear. Any change in the signal return time is interpreted as motion, and the sensor responds by keeping the lighting on. Some products use patented signal processing circuitry to automatically adjust the signal detection threshold to compensate for changing levels of activity and airflow. This feature helps to eliminate false ON activation. Ultrasonic sensors are best suited for monitoring partitioned areas and areas with large objects, such as furniture, that are likely to block the field of view of PIR sensors.

For spaces in which neither a PIR nor an ultrasonic sensor is practical, a dual-technology device using both PIR and ultrasonic sensing can be installed. Both types must detect occupancy to turn lighting on, while continued detection by only one technology will keep lighting on. These sensors are best suited for office areas with cubicles, general workplaces, warehouse and storage facilities, cafeterias, and public areas in commercial facilities.

Generally, a ceiling-mounted dual-technology sensor consists of two components: the sensor head and the power pack. The exposed sensor head, containing the sensing element and logic circuits, is mounted above the area served. The power pack, usually containing both a 24VDC power supply for the sensor and a 13A relay for switching lighting loads, is typically recess-mounted in the space above a ceiling. An optional feature for a ceiling-mounted fixture is a secondary relay, which can be used to send control signals to an HVAC system, based on occupancy detection.

An outdoor motion sensor that uses PIR technology is suitable for a wide range of commercial industrial settings, including parking areas, storage facilities, loading docks, and walkways. A temperature compensation feature ensures uniform performance in extreme hot or cold weather and during temperature fluctuations. Surge suppression minimizes the likelihood of damage due to electrical surges.

Mechanical and electric time switches activate lighting loads based on a specified interval. Often these switches can replace conventional wall switches without the need for additional wiring. Furthermore, the device has features that provide additional functionality, such as user-adjustable settings like time-out period, time scroll, one-minute flash warning, and beep warning features. It's also compatible with central time clocks or building management systems.

A photosensitive control unit operates a lighting circuit that adjusts to ambient lighting levels. In response to the photo control unit, a switching system will turn on lamps in a specific pattern, such as one or more contactors/branch circuits or a portion of a branch circuit, to provide typically one-third, half, or two-thirds of full light output in an area. Photo sensor units are available as two-component systems with externally mounted sensors connected to a remotely mounted electronic module via low-voltage wiring, making it convenient to adjust operational set points from inside the building.

A centralized programmable control system holds the on/off time sequence for numerous lighting circuits in its memory. Pulse initiation of the control signal, generated from the unit's internal clock, can be sent throughout the building by a communications bus or other means.

Dimming control schemes.

Manual or automatic dimming equipment, which can respond to many inputs, allows the illumination of a space to be set at any desired level. The semiconductor used in a dimmer circuit is called a triac. The triac provides phase control, meaning that it regulates the current to the lighting load by only conducing during a selected part of the AC power cycle.

Incandescent dimming devices include wall box-type units rated as high as 2,000W that can fit in a single-gang electrical device box. Some models allow dimming from two or more locations, which previously required a remotely controlled dimmer module.

A line voltage incandescent dimmer can't be used with fluorescent or low-voltage incandescent luminaires, or with a motor load. By conducting during only a portion of the AC power cycle, triacs produce a chopped output. This irregular current waveform is satisfactory for an incandescent filament, but an inductive load, such as a magnetic ballast, transformer, or a motor, can be damaged.

An increasing number of designs call for the dimming of fluorescent lamps and low-voltage incandescent lamps. Fluorescent and low-voltage incandescent lamps can use either a magnetic or an electronic ballast or transformer, and dimmers are designed for each type. When a manufacturer indicates that a dimmer is intended for a particular type of electronic ballast, no other type should be used.

Automatic fluorescent lamp dimming can be accomplished in three ways:

  • The first dimming method uses a photo sensor that responds to change in luminance by varying the voltage over a range of 1VDC to 10VDC in a two-conductor control circuit. The analog voltage, or modulated current, from the photo sensor connects to the input of a dimming-type fluorescent ballast. However, this control circuit doesn't provide feedback on its operation. This type of control circuit can offer a dimming range from 1% to 100%. Generally, the photo sensor and the dimming ballast should be compatible with one another.

  • A second dimming control method sends digitally-encoded pulse signals over a two-conductor control circuit, from the photo sensor unit to a microchip within the ballast, rather than a variable control voltage. Since the transmitted digital control signals are noise- and interference-free, reliability is ensured. Modulating the frequency of the control signal establishes the ballast's output and the light level. Pulse-coding methods are usually proprietary, so the dimming ballasts and photo sensors must come from the same manufacturer.

  • A third dimming control method uses a non-proprietary protocol that offers both dimming and switching functions via digital signals over the two-conductor control circuit. The digital addressable lighting interface (DALI) is a recent effort by a group of U.S. and European lamp/ballast/fixture manufacturers to provide an economical control method. The system provides digital communications between a controller and an individual lighting fixture, which could contain a linear fluorescent, a compact fluorescent, or even an incandescent lamp. Since each fixture, or ballast, has a microchip with its own address, it can be controlled individually. The data sent to the microchip is held in memory and retained even if a power loss occurs. DALI control systems are more expensive than 1VDC to 10VDC analog control systems but less expensive than the more complex bus control used in building automation systems. The Table above compares an analog 1VDC to 10VDC control system and the DALI system.

In addition to providing energy savings, modern lighting controls offer convenience and the ability to change light distribution to accommodate changes in workspace configuration, schedules, and activities. Keep in mind that many states have lighting power budget requirements and control requirements that define the maximum lighting watts/sq ft allowed and where control systems must be used. At the same time, how much you know about lighting control technology will become even more important as more states pass laws allowing electric energy providers to use real-time pricing. As this type of time-of-day rate scheduling and billing becomes more common, integrating control systems into facility lighting specifications will go from a useful luxury to a must-have feature.

Sidebar: Minimizing Early Wear of Fluorescent

Lamps Operating ceiling-mounted fluorescent lamps through occupancy sensors means that they are switched on and off frequently. This frequent start-up of the lamps reduces their operating life, because the electrodes at each end of the tube wear out at an accelerated rate, especially on an instant-start ballast. The instant-start type of electronic ballast is widely used because of its low cost.

Thus, manufacturers have developed “programmed-start” electronic ballasts for occupancy sensor-controlled fixtures. Programmed-start means that the lamp cathodes are preheated for a calculated period of time before the lamp operates, similar to the older rapid start operation of T12 lamps. This way of initiating lamp operation is called “soft-starting,” and it can increase the life of T8 and T5 linear fluorescent lamps. This type of electronic ballast may be the standard for the future.

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