Lighting accounts for 30 to 50 percent of the energy consumed in a typical commercial facility. In retail stores and other buildings with a great deal of accent or display lighting, lighting may account for 70 percent of the energy consumption or more. Following are a few important lighting terms:
Watts (W) are the standard unit of measurement of energy demand of an electrical device. Lamp wattage ratings show the amount of energy being drawn by the lamp any time it is in use.
Kilowatt-hour (kWh) is the standard unit of energy consumption measured by an electric meter and billed for by utilities. One kWh is equivalent to one kilowatt (1,000 watts) of electrical demand in use for one hour.
Lamp is the general term for any device that converts electricity into light. Incandescent light bulbs and fluorescent tubes are the most common lamps in commercial buildings.
Ballasts regulate the voltage and electrical current supply to fluorescent and high intensity discharge (HID) lamps. In a typical fluorescent lighting fixture the ballast(s) account for as much as 15 percent of the total electrical consumption.
Lumen is the basic measurement of light output.
Lighting Efficiency (or lighting efficacy) is the ratio of lumens that the lamp outputs to the watts that are input. The more lumens produced per watt, the more efficient the light source.
Luminaries are the complete lighting units including the lamps, ballasts, power supply connections, protective housing, mounting and other components designed to distribute light including reflectors, lenses and diffusers.
Lighting and Energy Use
Lighting can waste energy in four basic ways:
· Inefficient Light Sources. Lighting is inefficient anytime the lamp demands more electricity (watts) than another available technology to produce the same amount of light (lumens).
· Transmission Losses . Dirt, yellowed luminaries lenses, or obstructions can prevent some of the light produced by a lamp from reaching the intended area. If the light source is located too far away from the area to be illuminated, most of the light will be lost before reaching that area.
· Overlighting . There are accepted, recommended light levels for different visual activities. Overlighting occurs when more artificial light is used than is needed.
· Generation of Heat . Artificial lights give off heat in addition to light energy. This heat must be dissipated by the building's air conditioning system. Improved lighting can reduce air conditioning load and thus lower energy costs.
Reducing Lighting Energy Use
There are three simple guidelines to reducing lighting energy use:
1. Reduce lighting operating hours by turning lights off when they're not needed.
2. Reduce light levels wherever there is more light than really needed.
3. Replace current lighting systems with more efficient lighting and lighting control systems.
Good lighting design can also result in other benefits such as improved visual comfort (reduced glare, improved contrast, better color rendition) and lower maintenance costs.
Simply switch off lights when they are not in use. Turning lights off just two hours per day (when the room is unoccupied or when daylight is adequate) will reduce energy costs by 15 to 20 percent in the typical commercial setting. Turn off exterior lighting except as needed for safety, security or other specific purpose. Make sure exterior lights are not left on in the daytime.
Use partial lighting before and after "public" hours, when employees are present but before customers arrive. Most facilities now have dual switching systems that allow just half of the lights to be on in an area for low-level lighting needs such as stocking shelves, cleaning and rearranging merchandise. Selecting the right size room for meetings can also reduce lighting energy; lighting a large conference room for use by just a small group is inefficient.
Reschedule After-Hours Activities
Many evening activities, such as cleaning, meetings or contractor work, can be rescheduled to time periods when the lights are normally on anyway. Cleaning can sometimes be scheduled for early morning or late afternoon, or on weekend days when rates are lower and daylight prevails. Employees, as well as cleaning staff and contractors, should be informed of the need to turn off lights as they finish work in each room, and to reduce light levels when possible.
Lighting levels are often higher than they need to be. Removal of unneeded lamps is an easy solution, if it will not affect the comfort, productivity or safety of occupants. For example, in a typical office where lighting is operated 3,120 hours per year (10 hours per day, 5 days per week), removing a single 100-watt incandescent light bulb will save 312 kWh of electricity every year. At a typical commercial electrical rate of $0.10 per kWh, this yields annual energy cost savings of $31 per lamp removed.
Dirt on lamps and fixtures can reduce lighting output by as much as 30 percent. Lamps, lenses and reflective surfaces should be cleaned at least annually, or whenever replacement lamps are installed. More frequent cleaning may be necessary in areas that contain a lot of grease, dust, smoke or other airborne particles. Frequent cleaning may increase light levels, which will in turn permit de-lamping or the use of lower wattage lamps.
Educate your staff about energy and environmental issues. Stress the importance of energy savings on overhead costs and improved profitability. Tenants and landlords should work together to improve lighting quality and energy efficiency.
Providing strong lighting only to the area where work is performed (i.e. the desktop), rather than overlighting the entire room area, is a good way to reduce energy costs. Desk lamps, bench lamps and other smaller lights placed closer to the work area can reduce the need for overhead lighting.
There are a variety of low-cost occupancy sensors, time-based controls and photocells available in the market that can significantly reduce lighting energy costs by automatically turning off lights when they are not needed, or reducing lighting levels in response to the availability of natural daylight.
Photocells are particularly effective at reducing the hours of operation of typically high-wattage outdoor area lights by turning them on at dusk, and off at dawn. Compared with manual switching based on employee arrival, this often reduces usage by several hours per day, and needs no adjustments for seasonal lighting variations.
Additional light switches can be installed to provide sector lighting control strategies, or to allow fewer lights to be on in an area for low-level lighting needs, such as stocking shelves and cleaning.
Re-lamping with Incandescent Bulbs
Compact fluorescent (CF) lamps are the preferred replacement choice for most situations, but if incandescent lamps must be installed, re-lamp according to the following guidelines:
· "Energy saver" lamps provide almost the same lumen output as standard incandescent lamps; typically, a 55W instead of a standard 60W, and 95W instead of 100W.
· Where possible, install one large bulb in place of two smaller ones. Two 55-watt "energy saver" incandescent lamps produce 1,780 lumens; they can be replaced with one 95-watt bulb, which produces nearly as much light, saving 15 watts of electricity.
· "Extended life" incandescent bulbs are only recommended for places where it is difficult to replace them. They produce fewer lumens per watt than standard incandescent lamps.
Replacing with Compact Fluorescents
Compact fluorescent (CF) lamps are high efficiency alternatives to incandescent bulbs. Incandescent bulbs produce between 8 and 24 lumens per watt, compared to 40 to 90 lumens per watt for CF's. Also, a compact fluorescent will last 10 times as long as an incandescent, with an expected life of 7,500 to 10,000 hours. Although initially more expensive, a compact fluorescent delivers the same amount of light for about one-fourth the energy. Due to energy cost savings, reduced replacement costs and lower waste heat generation, CF lamps make an attractive energy conservation opportunity. Replacing a 60W incandescent with a 15W compact fluorescent will provide cost savings of about $46 over its life cycle.
Luminaire Repair, Retrofit or Modification
Broken, yellowed, or hazy globes, lens covers or diffusers on luminaries can reduce lighting output or deflect light away from the intended application. Replacement covers are available for most fixtures including new designs that may concentrate light better than the original cover. Many luminaire vendors will allow prospective buyers to experiment with lens covers to select the best lighting and appearance for each area.
Reflectors should be periodically inspected for surface damage and alignment. Reflectors direct light out of the luminaire, but must be properly aligned to project light in the intended direction. Installation of reflectors may permit the use of lower wattage lamps or de-lamping strategies while still maintaining the same light levels.
Replace Fluorescent Lamps
Fluorescent tubes come in many varieties of wattage, size and "color temperature." Replacement lamps must be compatible with existing ballasts, housings and mounting terminals. Color temperature will determine how the area will look, and the effects of color rendition of objects, skin, etc. Lighting vendors can suggest the best color ranges for specific applications.
The "T8" lamp and electronic ballast are the current standard in energy efficient fluorescent lighting technology. New construction and major retrofits should utilize T8 lamps and electronic ballasts, which cost only slightly more than less efficient alternatives. A 4-foot T8 lamp with an electronic ballast will draw just 28 to 32 watts. Completely retrofitting an existing building from the older T12 lamps with standard magnetic ballasts to T8 lamps and electronic ballasts will payback in two to four years for most commercial buildings. For buildings, such as hospitals, with continuous operation the payback period is generally less than one year.
Without changing ballasts, the standard 4-foot, 40W fluorescent lamps (F40-T12) can be replaced with 34-watt T12 lamps (F34-T12), with only slightly reduced lumen output and at minor additional cost. Comparable 8-foot lamps are also available. The F34-T12 series is a good option in "one-for-one" replacement strategies, especially when existing T12 lamps are in need of replacement.
It is frequently cost effective to replace old ballasts at the same time as fluorescent tubes. The ballast is an integral, energy consuming part of any fluorescent or high intensity discharge (HID) fixture, and an important determinant of the energy efficiency of the entire lighting system. A ballast starts the lamp and regulates voltage and current during operation.
Electronic ballasts have higher efficiency and life span than magnetic ballasts, and reduce the undesirable waste heat, flicker and hum associated with traditional fluorescent lighting.
Spotlights and Recessed Fixture Improvements
Most spotlights are used for general area or broad-beam lighting. A small reduction in lumen output is generally not important, so lower wattage parabolic area reflector (PAR) lights can be used.
Standard light bulbs and floodlights radiate light in all directions. When incorrectly used in recessed downlight fixtures, a good deal of the light is "trapped" by the fixture. Reflector lamps are generally preferred for this application. A 75W incandescent ellipsoidal reflector (ER) will project the same amount of downlight as a standard 150W flood, reducing energy use by 50 percent.
Halogen gas-filled bulbs increase lumen output and have a longer life than standard incandescent lamps. They produce a tight beam of "sparkling white" light that is good for merchandising displays and other focused applications. A 90W reflector halogen can replace a conventional 150W flood. If a less focused beam is preferred, a non-reflector halogen or a compact fluorescent may be suitable.
Outdoor Area Lighting
There are a number of long-lasting, high efficiency alternatives for parking lot and general outdoor lighting. These include high intensity discharge (HID) fixtures using mercury vapor, metal halide or high pressure sodium. They come in a range of sizes and have different performance characteristics.
Combining de-lamping and re-lamping strategies can result in highly favorable efficiency improvements.
For example, assume a 180-square-foot perimeter office with three 4-lamp, 40W standard fluorescent, ceiling-mounted fixtures. Assuming the lights are left on an average of 10 hours per day, five days per week, 52 weeks per year, the annual electricity consumption is 1,248 kWh. The following simple, no-cost and low-cost strategies can be applied:
1. Remove (de-lamp) two lamps from each of the fixtures closest to the windows and the door. This measure alone will save 416 kWh, or 33 percent of the lighting energy usage.
2. Replace (re-lamp) the remaining eight lamps with 34W T12 lamps. This will save an additional 10 percent.
3. Manually turn off the lights for two hours per day (when the office is unoccupied, during lunch, or when adequate exterior daylight is available). This will save an additional 141 kWh, or 11 percent.
In composite, the annual energy consumption could be reduced from 1,248 kWh to 565 kWh, or 55 percent through these simple measures. Additional savings could be achieved through ballast and T8 replacement, occupancy sensors, task lighting and other small investment opportunities.
Further cost savings may result from reduced air conditioning requirements since reducing the lighting in the building also reduces the cooling load. Conversely, more space heating may be required, although space heating energy is generally less expensive than space cooling energy.