Besides new lighting control products entering the marketplace, marketing efforts by these product manufacturers are on the rise.
After we squeeze every watt out of lamps, ballasts, luminaries, and light levels, where else can energy savings be found? The answer is literally at our finger tips: turn the lights OFF. With all of the development and attention paid to reducing energy in lighting systems, the fact still remains that turning lights OFF is the most cost effective means of capital savings and energy conservation available. However, doing so requires human activity that, like a weatherman, is not always reliable.
Switching strategies
OK, so what are these lighting controls that are going to save owners energy dollars? Let's take a look at the most simple: the snap switch. Snap switches (single pole, 3-way, and 4-way) can be used individually to switch all of the lamps in a room, or they can be used in tandem to provide multi-level switching control. Dual control lighting, designed in one of two ways, provides the opportunity to reduce light levels and subsequently lighting energy loads in a space when full light output of the lighting system is not required.
Zone switching. Zone switching allows control of luminiares in front room-back room, side-by-side, or special task configurations. The advantage of zone switching is most apparent in large spaces such as multitask labs, open offices, multi-congregational sanctuaries, and multipurpose gymnasiums where lighting can be switched off in the zones where tasks are not performed. The disadvantage of zone switching is that it limits movement. Tasks cannot occur in more than one zone sequentially without switching lights as an individual moves from one task zone to the next.
Split swishing. Split switching or inboard/outboard switching is used in place of zone switching to provide three levels of even illumination where three lamp fluorescent luminaries are used. The advantage of split switching is that light levels can be reduced while still maintaining even lighting throughout the room. Three levels of light (one lamp on, two lamps on, or all three lamps on) provide considerable flexibility for daylight spaces or for spaces with tasks that require several different light levels but do not require full range dimming.
Split switching can also be incorporated into 2- and 4-lamp luminaire configurations. However, only two light levels can be achieved from these applications. In 4-lamp luminaries, the options are two lamps ON, or four lamps ON. Technically, you could switch all four lamps individually, providing four light levels if that degree of flexibility is justified. However, ballasting and balancing the light output may make this an undesirable choice. It may seem obvious, but it's important to note that 2-or 4-lamp split switching can reduce the energy consumed by half when full light output is not required.
Compact fluorescent downlights have become a major player for 2-lamp switching schemes. While 2-lamp electronic dimming ballasts for compact fluorescent lamps are becoming increasingly available and in popular use, 2-lamp switching of downlights provides a cost effective alternative to dimming, where full range dimming is not required.
In our designs, we use split switching almost exclusively in classrooms and of-rices where multiple levels of lighting are typically required. We also use split switching in healthcare facilities with overnight patient rooms. Corridors with high daytime light levels can typically be reduced by half for night time use. Sleeping patients and reduced caregiver activity make this a good energy saving alternative with a very low initial cost. (See advanced lighting control strategies on page 57.)
Dimming controls
The second most simplistic method of lighting control and energy savings is to turn the lights down. Control technologies are currently available to dim incandescent and discharge lamps. While dimming is a very common practice for incandescent control, fluorescent dimming is beginning to be pursued seriously by several fluorescent ballast and control manufacturers. You should note that while energy can be saved in dimming systems, the energy saved by dimming incandescent lamps or discharge lamps is not proportional (below 40%) to light level reductions; more light will be lost than energy saved. In other words, the lumens-per-watt ratio (efficacy) of the system decreases as the energy consumption via dimming decreases, but not at the same rate. (See [ILLUSTRATION FOR FIGURE 1 OMITTED] on page 57 and [ILLUSTRATION FOR FIGURE 2 OMITTED].) In addition to system efficacy, the cost effectiveness (i.e. energy saved per dollar spent for dimming discharge lamps) should be scrutinized carefully where energy saving is the primary requirement for the space. Where full range dimming is required, the cost of dimming discharge lamps versus the cost of dimming incandescent lamps versus meeting energy requirements is left to the professional judgment of the lighting specifier. In an increasing number of cases, the choice is very difficult and should be evaluated very carefully.
Incandescent dimming. In spaces where incandescent lighting is appropriate, so are dimming controls. Incandescent dimming, as simple as it is, is not without its technological changes. Early dimming controls were variable resistors that, from an energy point of view, wasted as much energy as they saved. Autotransformer (magnetic core and coil) dimmers replaced resistor technology by reducing voltage to the lamp, thereby reducing the total energy required for operation. Solid state dimming, typically found in today's applications, uses transistors or thyristors as switching elements to control the power input to the lamp. Solid state dimming comes in many packages, from single pole dimmer switches to larger multiscene preset controls.
While incandescent lighting in spaces is severely limited by most energy codes, applications for its use still exist. The primary, large-scale use of incandescent lighting is in performance and theological spaces where changing light levels and limited audible noise is essential. Consider religious sanctuaries, as an example. Often, they contain large voluminous spaces with ceilings at 30 ft or more above a finished floor. Here, dimming controls are essential to the basic requirements of the space.
Energy codes aside, we typically design sanctuaries for 20% more light than recommended. The reason is simple: the dimming systems (in most cases multiscene presets) are essential to the function of the space and, therefore, will be specified with or without a high illuminance lighting design. By over designing the light level, a 10% energy/dimming high-end cutoff can be programmed into the control system. The high-end cutoff will not allow light levels to be switched higher than 90% of full lumen output and can not be altered except by the facility lighting control manager. The 10% energy reduction will reduce light level by 20% but increase lamp life by 300%. That means that the life of a quartz lamp, rated for 2000 hrs, will be extended to an average of 6000 hrs, which is significant for a space that operates an average of 15 hrs per week and where relatively expensive lamps are difficult to replace.
The dimming of discharge (fluorescent and high intensity discharge or HID) lamps is more complex than dimming incandescent lamps. However, dimming controls for discharge lamps, and fluorescent lamps in particular, have been available for quite some time. The dimming of discharge lamps requires dimming ballasts working in conjunction with dimming controls.
Fluorescent lamp dimming. In the case of compact fluorescents, even the lamps must be specified (four-pin instead of two-pin) specifically to work with the dimming system.
The fluorescent lamp is a negative-resistive load that requires a ballast to control the electrical input for starting and maintaining operation. Dimming controls designed to reduce voltage input, as in the case of incandescent dimming, will extinguish the arc in addition to reducing lamp life.
Fluorescent lamps can be dimmed from controls designed for standard magnetic ballasts, magnetic dimming ballasts, and electronic dimming ballasts. Like a low voltage incandescent lighting system, a fluorescent dimming control must be matched to the technology for which it is specified. Standard magnetic fluorescent dimmers provide full range dimming to 40% of rated lumen output.
Magnetic dimming ballasts, available for only 30W and 40W lamps, can provide full range dimming to 10% of rated lumen output.
Electronic ballasts for dimming compact fluorescent lamps can provide full range dimming to 5% of rated lumen output.
Electronic dimming ballasts for long fluorescent lamps can provide full range dimming to 1% of rated lumen output. To date, only one manufacturer of long fluorescent dimming ballasts and controls offers reliable full range dimming to 1% of rated lumen output. Several new manufacturers of fluorescent dimming ballasts and controls have recently entered the market, and several more are expected to be on the market by year end.
Fluorescent dimming to date is not a low cost specification item; it's not for every space and it's certainly not for every budget. As noted above, only one low wattage electronic ballast has proven its reliability in the market. Few would argue that the technology, reliability, and manufacturer's support is worth the price if fluorescent lighting and dimming is appropriate for the space. Unlike incandescent dimming, where the controls and luminaries are so inexpensive that over designing the light levels can justify dimming both in energy savings and in maintenance, the initial and long term costs of fluorescent dimming must be carefully evaluated. Spaces where we have found justification for full range fluorescent dimming are in medical exam rooms, conference rooms, and in daylight spaces where lumen maintenance and photocell controls are likely to be employed.
HID lamp dimming. While HID dimming controls are currently on the market, the technology is still developing and the cost effectiveness of full range dimming remains questionable. HID dimming and control systems must compensate for lamp sensitivities such as warm up time, color shift, and lumen degradation, which are standard operating issues. Because of warmup time, HID lamps are slow to respond to dimming. Lag time from low illuminance to high illuminance can take as long as 10 min. Instantaneous response can be attained by some dimming controls, but in a very limited illuminance range.
The color shift of HID lamps varies between lamp types. Low wattage, clear metal-halide (M-H) lamps can begin a color shift to blue-green in the range of 80% of full lumen output. High wattage, clear, M-H lamps will begin to shift at about 60%. High pressure sodium (HPS) will begin a significant monochromatic shift to yellow at about 50% of rated lumen output. Indeed, lamp manufacturers may void the lamp warranty if the dimming and control system specified is known to threaten lamp life and/or induce unrecoverable color shifts.
Multilevel switching, often referred to as "Hi/Lo," is another form of energy and illuminance control for HID lamps. Typical systems will operate HID lamps at full light output and energy consumption and at a reduced light output and energy consumption. The primary advantage to this type of system lies in low traffic spaces where occupancy sensors can switch lights to low to conserve energy when the space is unoccupied. and switch them to high when a person arrives. Bi-level systems are also appropriate for atriums, where photocells can be used to reduce the light level when a significant lighting contribution from daylight is present. We have used bi-level switching in multiuse high school gymnasiums to meet energy codes and maintain high illuminance levels for competition basketball.
The most recent development by one of the oldest manufacturers of multilevel ballasts and controls is a tri-level switching system.
Multilevel lighting controls suffer the same problems as full range dimming: Lamps switch from high to low instantaneously, but switch back only to about 85% of full lumen output instantaneously. Also, in a multilevel lighting system, lamps must always be started in the high mode; only after the lamps are warmed up to full lumen output can they be switched to low. The lamp takes between 5 and 10 min to warm-up to full bright.
Most manufacturers limit noticeable color shift by designing multilevel systems that do not allow the low setting to be below the color shift point of the particular HID lamp. As with dimming ballasts and controls, lamp manufacturers may void warranties on products that threaten lamp life and color.
Low voltage lighting
Low voltage lighting specifications for accent lighting are increasing due to the relatively low input watts and high lumen output of the low voltage source (for example, a 50W halogen lamp rated for 950 lumens versus a common 50W A19 incandescent lamp rated for 750 lumens).
Low voltage lighting systems require low voltage dimmers and care must be taken to specify like systems. There are two types of low voltage transformers and, as a result, there are two types of low voltage dimmers. A magnetic low voltage transformer is an inductive load; it requires a dimmer that sees an inductive load. An electronic low voltage transformer is a capacitive load; it requires a dimmer that will see a capacitive load.
While line voltage lamps can be added to either system, the line voltage lamp, which is a resistive load, must be placed ahead of either the magnetic or the electronic transformer in the system.
Intermediate control technologies
Intermediate lighting controls include systems that incorporate timers or sensors to switch or dim lamps without human action. These controls include time clock controls, occupancy sensors, and daylight sensors. They can be used separately or in tandem in a space. Consider, for example, an office with significant daylight and a mobile occupancy. Occupancy sensors and daylight sensors can be combined to switch the lights OFF if the daylight illuminance level exceeds a preset illuminance level. The remaining lights can be switched OFF or ON by the occupancy sensor as people move through the space. A time clock could also be added to this scene by switching OFF the power supply to the room at a prescribed time. The primary disadvantage of this type of multisensor control is loss of control by the occupants; however, this can be resolved with advanced controls.
Photocells and timers
Including photocells and timers in a lighting design is an inexpensive way to ensure that lights are turned OFF when they are not required. Timers can be used to switch the lights OFF over a full floor or in an entire building before or after daily occupancy. Photocells will switch lights OFF if the daylight component of the interior lighting is great enough and switch lights ON when the daylight subsides.
Photocells. The types of spaces most often designed with photocell controls are atriums and sun rooms. However, any space with concentrated daylight present throughout the day is a candidate. Consider, for example, an office with predominantly east facing glazing. This space may not require electric lighting during the morning hours, but may require electric light in the late afternoon.
Lumen maintenance system. Photocell technology combined with dimming technology provides owners with an advanced lumen maintenance system, resulting in cost savings from reduced energy and maintenance.
What's a lumen maintenance system? It's basically a system that takes into account the natural lumen depreciation of a lamp, fluorescent lamps in particular. For example, if you assume a 30% loss due to lamp lumen depreciation, you can design a control system to account for this eventual loss. The initial lumen output of the lamp will be reduced by 30% and energy will increase during the life of the lamp to consistently maintain the 30% light loss. However, full energy will be consumed only at the end of lamp life, when the lamp has reached its rated lumen depreciation. Therefore, a significant amount of energy will be saved through out the life of the lamp, without a change in the light levels designed for the space.
Occupancy sensors
There are three kinds of occupancy sensors available: infrared, ultrasonic, and infrared/ultrasonic. They may be wall or ceiling mounted as individual units, or they can be specified as integral to a lighting switch. They are readily available from a variety of sources.
Occupancy sensors are notorious for switching lights OFF when rooms are occupied and switching lights ON from motion that is extraneous to the room or occupancy.
Sensors have varying range capabilities, in addition to sensing sensitivities. You should take care to select the right product for any given space. You also should be careful to select the right application for occupancy sensors. In spaces where fluorescent lamps are switched OFF and ON frequently, lamp life may be significantly reduced. (Remember, lamp life is rated at 3-hr starts.) While the lamp will gain usable life because it's switched OFF, you must decide if the OFF time will compensate for the reduced rated lamp life.
Occupancy sensors are best for small, infrequently used spaces such as rest rooms, conference rooms, storage rooms, copy rooms, and private offices.
A recent development in occupancy sensors is a personal occupancy sensor. This device (by one manufacturer) provides a 15A power strip containing six receptacles. Four of the receptacles are tied to a small personal motion sensing devise. When the sensor does not detect motion for a preset period of time, the four receptacles shut down power until occupancy or motion is detected once again. Task lights, radios, or video display terminals can be connected to the sensed receptacles while computers and clocks can be connected to the unsensed receptacles.
Advanced lighting controls
The most advanced control systems used today combine the technologies already discussed with microprocessors and low voltage relays to create some very powerful lighting controls.
The original low voltage systems started with momentary contact switches that controlled relays. By adding motor masters to control whole banks of relays, an entire floor of lighting could be switched OFF.
Now, an advanced lighting control can control each relay separately. The more relays employed in the system, the more control you have.
Advanced lighting control systems typically contain internal timeclock functions and can take input from occupancy sensors, interior and exterior daylight sensors, and momentary contact switches. The newest products will also take input from dimmers, which can control line voltage and low voltage incandescent lamps, fluorescent lamps, and hi/lo switching HIDs. The dimming and control adds a very powerful dimension to advanced lighting control systems by replacing numerous components and independent systems with one advanced control system.
While the concept of lighting controls is not new, the controls themselves are the next logical place to look for developments in energy conservation. In addition to new lighting control products entering the market place, marketing efforts by lighting control manufacturers are on the rise. However, the new wave of control sophistication is not without draw backs. Ballast and lamp manufacturers are faced with the task of once again taking a closer look at technologies that can operate effectively with switching, dimming, and other energy reducing controls for discharge lamps used today.
Carla Gallina is Senior Lighting Designer with Hammel Green & Abrahamson, Architects and Engineers, Minneapolis, Minn.