Harvest Daylight and Reap Rewards

The concept of daylight harvesting (also called daylighting) is simple. During the day when natural light is streaming in through windows and skylights, you don't need to use as much artificial light. You can either adjust lighting levels manually, or you can use an automated system that detects daylight levels (using photosensors), and automatically dims or brightens electric lights as required.

Making more use of natural light helps you to consume less energy, which reduces both your energy costs and carbon footprint. Lights that are dimmed or turned off typically emit less heat, which can help to reduce air conditioning costs. Dimming can also extend the life of a lamp, helping to further reduce costs (and landfill). And numerous studies have shown that people are happier in an environment that contains more natural light.

The cost and energy savings are especially important in commercial buildings, where lighting can account for up to 40% of the total energy spend.

A number of automated daylight harvesting solutions are available, consisting of dimmable luminaires (or lamps within luminaires), photosensors, and lighting control software.

The sensors have a photoelectric "eye" that measures the illumination in a specified zone. They transmit this information to lighting control software, which is programmed with acceptable threshold levels. If the illumination levels fall outside those thresholds, the software sends commands to dim or brighten the luminaires as required.

It is possible to implement pseudo-daylight harvesting that uses timers to dim and brighten luminaires at the same time every day, but this is a less satisfactory solution. Timers are not able to take into account things like whether the sky is clear or overcast, or whether people have closed the window coverings to reduce heat and glare, so often result in inappropriate levels of illumination.

Daylight harvesting can return maximum benefits in buildings that are occupied primarily during daylight hours, such as office buildings, schools and other government buildings.

Levels of natural light vary throughout a building affected by things like orientation, proximity to windows or skylights, and the colors of walls, ceilings and furnishings. To achieve the best results, you need a solution that is flexible enough to allow luminaires to be dimmed in different "zones" at different times and rates, and to different levels.

For example, you might select to enable daylight harvesting only for the first three or four banks of ballasts next to windows. The bank immediately next to the window, which receives the greatest amount of natural light, would be dimmed by the greatest amount. If required, dimming levels could gradually reduce as you move away from the window and the amount of natural light decreases.

The goal for successful daylight harvesting is to adjust electric light levels gradually enough that building occupants don't notice the change.

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