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What Is Daylight Harvesting?

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  • Written By: Felicia Dye
  • Edited By: Heather Bailey
  • Last Modified Date: 16 December 2014
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Daylight harvesting is an alternative energy option that has the potential to achieve several goals, such as reducing electrical demand and cutting costs. To do this, light that is produced by electricity is reduced in proportion to the available daylight. This tactic is generally used in commercial buildings.

The rise in concern for sustainability and cleaner energy tend to be major driving forces for daylight harvesting. This alternative energy option is commonly marketed as a method to reduce the use of fluorescent lighting, which is believed to be responsible for a significant portion of commercial energy bills. The concept by which daylight harvesting can be done is very simple, although implementing a system can be complex and expensive. It involves installing a system that allows artificial electrical lighting to be reduced or eliminated when there is sufficient sunlight.

There are two methods used to accomplish this: switching and dimming. A switching daylight harvesting system generally has three or four levels of electrical light intensity. These can range from zero percent to 100 percent. This means that when the system is at 50%, about half of the light illuminating a building should be from daylight while the other half is provided by electricity. A switching system is generally easier and cheaper to install than a dimming system, but the energy savings also tend to be less.

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Dimming systems provide more flexibility because there are more electricity reduction options. These systems usually allow electrical output to range anywhere from 1 percent to 100 percent. A dimming system, therefore, can result in greater savings because it has the potential to be more efficient. If, for example, only 46 percent of the necessary light needs to be provided by electricity, that exact amount can be used, whereas with a switching system the user would have to use 50 percent, resulting in waste. Although the savings can be higher with a dimming system, the initial cost is also higher due to additional materials needed and the increased complexity of installation.

There are two ways a daylight harvesting system can be controlled: manually or automatically. Manual operation requires a person to augment or reduce the electrical output when it is necessary. Automatic controls require a photosensor, which determines the current lighting needs and adjusts the electrical output accordingly.

Daylight harvesting tends to raise several concerns. To begin with, it is generally difficult to guarantee the performance of such a system, which can result in the disappointment of users who expect greater energy savings. The daylight penetration in a building or part of a building can present challenges that affect the system’s efficiency. There are also fears that this type of alternative energy strategy could have a negative effect on commerce due to customer perceptions.

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