Daylight harvesting reduces electricity demand and costs by reducing artificial lighting in proportion to available daylight. It is marketed as a sustainable alternative to fluorescent lighting, but implementation can be complex and expensive. Switching and dimming systems are used, with dimming offering more flexibility but higher initial cost. Control can be manual or automatic, but concerns include system performance and negative customer perceptions.
Daylight harvesting is an alternative energy option that has the potential to achieve several goals, such as reducing electricity demand and reducing costs. To do this, the light produced by the electricity is reduced in proportion to the available daylight. This tactic is generally used in commercial buildings.
Rising concern for sustainability and cleaner energy tend to be the main driving forces for daylight harvesting. This alternative energy option is commonly marketed as a method of reducing 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 is a question of installing a system that allows for the reduction or elimination of artificial electric lighting when there is sufficient sunlight.
There are two methods used to do this: switching and dimming. A switched daylight harvesting system typically has three or four levels of electric light intensity. These can range from zero percent to 100 percent. This means that when the system is at 50%, approximately half of the light illuminating a building should come from daylight while the other half is provided by electricity. A switching system is generally simpler and cheaper to install than a dimming system, but the energy savings also tend to be lower.
Dimming systems offer more flexibility because there are more electricity reduction options. These systems usually allow the electrical output to vary between 1 percent and 100 percent. A regulation system, therefore, can lead to greater savings because it has the potential to be more efficient. If, for example, only 46 percent of the light needed needs to be provided by electricity, that exact amount can be used, whereas with a switch system the user would have to use 50 percent, resulting in waste. While the savings may be greater with a dimming system, the initial cost is also higher due to the additional materials required and the increased complexity of the installation.
There are two ways to control a daylight harvesting system: manually or automatically. Manual operation requires one person to increase or decrease the electrical power as needed. Automatic controls require a photo sensor, which determines current lighting needs and adjusts electrical output accordingly.
Harvesting in daylight tends to raise several concerns. To begin with, it is generally difficult to guarantee the performance of such a system, which can lead to the disappointment of users who expect greater energy savings. The penetration of daylight into a building or part of a building can present challenges that affect system efficiency. There are also concerns that this type of alternative energy strategy could have a negative effect on trade due to customer perceptions.
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