Lighting
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Daylighting


An Easy Way to Improve a Building's Efficiency
Lighting Controls
Additional Benefits
Cost Effectiveness

Daylighting An Easy Way to Improve a Building's Efficiency
Artificial lighting accounts for a substantial portion of the electricity used in buildings. Daylighting is the effective use of natural light in buildings to minimize the need for electric light during daylight hours. Increasing levels of daylight within rooms can reduce electrical lighting loads by up to 50% in some cases.

A well daylit building can often provide sufficient natural light for general work activities for a substantial part of the year. The amount of energy savings that can be realized through daylighting will be affected by factors such as building shape, building orientation, building materials used, and the orientation of work areas in relation to windows. Also keep in mind that with daylight comes heat. It is important to avoid overheating that may stem from excessive direct daylighting by using window coverings such as drapes, shades, and blinds.

Lighting Controls
Daylighting will not reduce energy consumption unless users turn off or reduce the use of unnecessary artificial lights. This can be achieved by using lighting controls. Lighting control systems can provide constant lighting levels by blending artificial lighting with daylighting to improve building energy efficiency. Lighting control options include on/off switching, dimmers, and multi-level cut-off systems. Manual on/off switching, timers or occupancy sensors are simple systems with a low to moderate cost. Occupancy sensors use infrared detection or ultrasonic wave detection. Dimmers and multi-level cut-off systems are typically more complex and more costly. Multi-level systems may involve wiring different groups of lights together to operate off sensors with different settings. Dimmer systems require special ballasts when fluorescent or high intensity discharge lamps (HID) are involved. Some controls integrate daylighting sensors, which use light detection with occupancy sensors, which use motion detection, into a single package. All three systems operate manually or automatically.

Additional Benefits
Besides energy savings from reduced lighting loads, there are other indirect benefits from daylighting. Human health and productivity can be enhanced with sound daylighting designs. Some studies have indicated significant increase in productivity (up to 15%) and reduced absenteeism for office workers through the use of effective daylighting. Recent studies in California demonstrate a strong statistical correlation between daylighting and improved sales in retail stores. Similarly, daylit classrooms are being shown to result in faster learning and healthier students.

Cost Effectiveness
Effective daylighting design involves balancing the elements of artificial lighting, solar heat gain, heat loss through glazing, and internal sources of heat gain. Daylighting must be integrated with electric lighting, heating, cooling, and ventilation systems as well as occupant task and movement patterns. Successfully doing so will provide a more comfortable and energy-efficient building. Whether you are designing a new building or retrofitting an old one, you need to perform extensive computer modeling and simulation. To be cost-effective, the savings on lighting and cooling must offset the costs of buying, installing, and operating daylighting features in a reasonable amount of time.


Sources: US DOE FEMP "Greening Guidelines", US DOE NREL "High Performance Building Research: Daylighting", US DOE EREC "Daylighting for Commercial, Institutional, and Industrial Buildings"

 

   
 
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