Daylight harvesting systems are typically designed to maintain a minimum recommended light level.
In a closed-loop system, the photosensor detects the total photometric amount of light, from both daylight and electric sources in the space.
[7] In both the open- and closed-loop configurations, the signal from the photosensor must be carefully calibrated to accurately indicate the effect of exterior daylight variations on the light level on 'important function' areas in the space.
They have the potential to save more energy, because they can reduce electric light output when daylight can only partially meet the needs of the space.
[14] Savings are very dependent on the type of space the light harvesting control system is deployed in, and its usage.
Such spaces have included offices, atria, interior public multistory plazas and shopping mall courts, and schools.
[15] Impressive energy savings estimates may not be realized in practice due to poor system design, calibration, or commissioning.
[17] One method of predicting energy savings is to use commercially available software programs, such as TRACE 700 or (freeware) DOE-2, which considers thermal loads.
Dividing this cost by the annual energy savings provides a "simple payback", the number of years for the system to pay for itself.
[21] Thus green building practices are increasing the production of daylight harvesting components, leading to lower prices.
The code encourages automatic daylight harvesting in secondary zones by awarding power adjustment factor credits that can be applied to the lighting design.