Saving Energy in the Lighting

Tips & Tricks

Saving Energy in the Lighting
A fourth of all electricity sold in the United States is used for lighting. Most of this lighting is used in stores, offices, warehouses and factories. It is strange, then, that conserving energy with lighting projects is not a high priority for most businesses. They assume lighting is a fixed overhead item that cannot be substantially reduced as an expense.

One mistake businesses make is to concentrate on first cost and purchase the cheapest lamps. They do not bother to consider the life cycle cost of these lamps. This can be a big mistake, given the 20,000 hour life of a typical fluorescent lamp. Installation of more efficient lamps can pay for their modest extra cost many times over. Industries that ignore this reduce their own competitiveness by operating under an escalating overhead, increasing with the electric rate.

Any modifications to the original lighting design at a facility should be done so that the quality of the lighting environment is not diminished. Exact illumination levels have been established to be maintained for specific tasks in the workplace. A number of inexpensive projects can be done, however, that do not significantly affect the light levels. They can be implemented by the maintenance staff, often without engineering design or approval required.

• Use fluorescent lamps for interior lighting
  Fluorescent lamps are much more efficient than incandescent lamps and should be used where possible, including task lighting and down lights. Compact fluorescent lamps are available that can be screwed directly into incandescent sockets. Thus they provide inexpensive lighting without sacrificing the convenience of incandescent lamps.
  
  High intensity discharge (HID) lamps are more efficient than incandescent flood lights and should be used in their stead. HID lamps are best suited for large interior spaces with a high ceiling such as lobbies and atriums. They are also ideal for locations that are hard to access, such as mechanical rooms or auditorium with high ceilings. HID lamps have a longer lifetime than either fluorescent or incandescent bulbs and do not have to be changed as often. Incandescent light sources are still best for some applications, such as pipe basements, housekeeping closets and other areas with special requirements such as darkrooms, photo labs and studios. Limited use of incandescent lamps in conference rooms and dining areas that need lamps to be dimmed is common, although fluorescent dimming systems are becoming more competitive and commonplace.
  
  
• Arrange fixtures to suit furniture arrangements
  A general guideline for locating fixtures in a room that does not have fixed task locations is to position fixtures within 2 or 3 feet of walls. Then arrange fixtures in a regular pattern to provide a minimum light level, using task lighting at individual work stations.
  
  If the work spaces are well defined or the location of furniture known a general lighting layout is not necessary. Instead, lights can be positioned directly above the work surface and located in non-task areas to provide a lower ambient light level. The latter include aisle space and such traffic locations as doorways. Lights should not be placed in the arc of a door swing as area lighting in the rest of the room will generally provide adequate illumination there.
  
  These modifications to traditional lighting schemes are possible because the IES stipulates an ambient or average light level at the work surface. The zonal cavity calculation method generates this value in a space and when lighting designers specify fixtures according to these figures, the results can be deceptive. As an example, consider a common lighting design situation.
  
  Two three lamp fixtures in a small office may produce a calculated light level of 60 footcandles, while the light measured directly beneath either fixture may be 120 or more at the desk top level. One of the fixtures can be eliminated entirely. There will still be good light at the work surface and adequate light in the rest of the space, where only 20 or 30 footcandles are needed. The only contingency to this scheme is to insure that the contrast is not excessive between the work surface and its environs. In small office with light colored walls this should not be a problem.
  
  As another example consider a laboratory or shop with built in work tables and work benches. Adequate light can be provided by a row of fluorescent fixtures. They should be centered over the front edge of wall mounted tables and perpendicular to double sided tables in the middle of the room. Since fluorescent fixtures emit more light parallel to the axis of the lamps than crosswise so a solid row of lamps may not be necessary. Lights over open floor areas can be omitted altogether or reduced to provide a minimum level of light for contrast.
  
  A final case is a large storage room. If the shelve locations are fixed then fixtures located lengthwise over the aisles will make the most efficient use of lighting. If the shelve locations are not well known then a good alternative is to run fixture rows at 45 degrees to the room dimensions.
  
  In all of these cases a degree of flexibility can be built into the design, especially if a large floor space is to be illuminated. Each fixture can be wired with a few extra feet of flexible cable to permit shifting it in a variety of positions in the ceiling grid. They can even be wired with a quick disconnect cable so that fixtures can be moved from one space to another as the floor plan changes or lighting needs vary. This will cost a little extra up front. However, if the space usage is expected to change frequently this flexibility can save the cost of a complete rewiring job with each remodeling.
  
  
• Limit decorative lighting
  Lighting in special areas such as conference rooms, lobbies, auditoriums and waiting rooms should be kept simple and functional. Special treatment for architectural purposes should use efficient fluorescent or HID lamps and should, where possible, double as general illumination. Decorative lighting of the building exterior should only be done if it is incidental to a functional lighting system.
  
  
• Control exterior and parking area lighting
  Exterior lighting of walkways and building entrances can remain on during daylight hours or at other unnecessary times. If these lights are on a dedicated circuit they can be turned on and off independently by an electromechanical timeclock. Work hours do not always coincide with the hours of darkness. Often the exterior lights will burn when in is light out either before or after business hours. The time clock will automate this function and save the staff the trouble. It will have to be reset periodically, though, as the seasons pass. A photocell connected in series with the time will resolve this problem and further reduce the time the lights are in use.
  
  Lighting for parking lots and parking garages will benefit from these controls as well, to insure the lights operate only when needed. Further savings are possible from circuiting the luminaires in logical groups that can be cycled on and off during the night. For example, a multi-level parking garage can leave only one level on during the off hours. This will work especially well for buildings with an integral garage. Such facilities often have only a single access door after close of business, so most parking will be near this entrance anyway. Parking lots can follow the same method, security needs notwithstanding.
  
  
• Use separate work station switching
  Large work spaces with individual work stations separated by partitions are common in laboratories and business offices. When a single person works late the entire space must be lit. An energy efficient alternative is to switch the lights so that one level will provide area lighting, then other switches at each logical work area will activate overhead lighting specific to that area.
  
  
• Maximizing Use of Daylighting
  Any room with outside windows has daylighting available to supplement the artificial luminaires. There are three types of daylight that can enter a conditioned space: direct, indirect and reflected. Direct light is the least desirable because it can cause problems from glare and it also has the highest contribution to the cooling load for a space. Reflected light can have similar consequences unless it is carefully controlled.
  
  Some architectural features can be enhanced to increase the natural lighting available to a space. Reflective sills and properly angled venetian blinds can be used to amplify the flow of light through windows or opaque openings such as glass brick walls. Even directing the light straight up to a light colored ceiling will help, as the reflected light from this ceiling will reach deep into the room.
  
  Landscape features are also helpful to direct more natural light through windows. A reflective area on the ground beneath a ground level window - of gravel, a light colored wood or concrete - will direct more diffuse light through nearby wall openings. Carefully trimming shrubs, trees and ground covering around windows will also help. These plantings may be desirable around windows facing south or west in the summer, however, to prevent direct light from heating up the building excessively in the late afternoon. Many people will trim the plants anyway and use blinds or shutters when direct lighting is a detriment.
  
  The incentive for increasing natural lighting is that it is the best for color discrimination and detailed work such as drawing, painting or drafting. artificial lighting can be designed to approach the natural ideal, but no further. Consequently any method that can increase the natural light in a space will enhance the lighting environment, thereby improving the productivity and attitude of the people within.
  
  Another factor of daylighting to consider is that windows with closed blinds or curtains have a higher insulation value. This is offset by the fact that the lights in a room also generate a portion of heat that must be removed by the air conditioning. This may be as much as ten percent of the total load. With the exception of direct lighting, though, it is generally an energy saver to take advantage of the daylight and pay the small penalty in higher air conditioning cost.
  
  The electricity savings made possible by increased use of daylighting can take several forms. In a space that can turn off all lights when outside conditions are favorable, the total lighting cost can be considered the net savings. Even though the available natural light varies through the day and from season to season, the annual electricity savings could be as much as 60% of the lighting bill.
  
  A final alternative is to put the lights in a daylit space on a multi-level switching system. If the space has three-lamp fluorescent fixtures, for example, the ballasts can be modified to permit one, two or three lamp operation of the lights for three separate ambient light levels. This provides the flexibility of supplementing the daylighting the minimum necessary to provide the proper total footcandle levels.
  
  Each of these systems will permit immediate savings, depending on the type of controls used and the extent to which the present switching must be modified. The cost and payback calculations can be complex, and will be detailed in the forthcoming section on controls.
  
  
• Reducing Illumination Levels
  Use of task lighting can reduce the footcandle levels in a space and reduce the electrical energy demand by 20% - 50%. Good areas to consider for this M & O are large open office areas where each workstation has a desk lamp, such as an engineering office that provides each drafting table with a lamp. In such instances the overhead lighting is no longer used to provide a task-specific illuminance, but serves only to supplement local light sources at each desk.
  
  Light levels can also be safely reduced in non-critical areas such as hallways, lobbies, waiting rooms, storerooms, mechanical rooms and restrooms. There are a number of ways to reduce the illumination levels. The best method to use depends on the type of lamps to be modified, incandescent or fluorescent. The energy saved will be in direct proportion to the reduction in wattage.
  
  
• Project Strategy
  It is important before beginning a major lighting retrofit project to first become familiar with the lighting environment of your business. Doing one or two of the M & O's is a good way to understand lighting and to become familiar with the equipment and technology.
  
  A strong incentive, other than simple energy savings, concerns the effect of lighting on performance, accuracy, visual comfort and sometimes even morale and attitude. If your project is planned carefully and implemented properly not only will there result a savings in energy usage, but the working environment will be improved.
  
  

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