Daylight harvesting systems use daylight to offset the amount of electric lighting needed to Properly light a space, in order to Reduce energy consumption . This is accomplished using lighting control systems that are able to switch over to changing the light. The term Daylight Harvesting has become standard in the fields of lighting , sustainable architecture , and active daylighting industries.
System design and components
Daylight harvesting systems are typically designed to maintain a minimum recommended light level .  This light level will vary according to the needs of the space; for example, the common recomended standard for offices is 500 Lux (or around 50 footcandles ) on the desktop. 
All daylight harvesting systems use a light level sensor, a photosensor , to detect the prevailing light level, luminance or brightness , in open-loop or closed-loop systems. Photosensors are used to adjust electric lighting based on daylight in the space.   In an open-loop system , the photosensor detects the amount of available light, and can be placed on the building’s exterior wall or roof, or inside the building facing the window or skylight. In a closed-loop system, the photosensor detects the total photometric amount of light, from both daylight and electric sources in the space.  For example, in the office, closed-loop photosensor can be placed on the ceiling facing the desktops in order to detect the amount of light on the work surface, as the sensor on the desktop itself would be impractical. In both the open- and closed-loop configurations, the signal from the photosensor must be carefully calibrated to reflect the effect of daylight variations on the ‘important function’ areas in the space. 
Control modules and dimming
The signal from the photosensor is made by a lighting control system , an automated light switching device, in the electric lighting system which can reduce the electric lighting, by shutting off or dimming fixtures as appropriate.  If the electric lighting is dimmable, then the artificial lighting can be continuously adjusted. If the electric lighting is on-off only, then an electric lighting fixture or lamp must remain at full output until daylight. Non-dimming variants include having multiple non-adjacent light fixtures such as alternate units in the ceiling ‘grid layout,’ or daylight source adjacent, or linked for moduleon-off switching. Another variation of on-off switching is the switching mode (sometimes referred to as “bi-level switching”), in which multiple lamps in a single light fixture can be switched on and off independent of each other. This allows for typically one or two steps between full output and zero.  
Dimming systems are more expensive than on-off systems. They have the potential to save more energy, because they can reduce their energy consumption when they can not meet the needs of the space. However, dimming systems may also require a little more energy for their basic operation.  If a dimming system is well-calibrated, the occupants of the space will not be affected by the changes in the light of daylight harvesting.
Several studies have recorded the energy savings due to daylight harvesting. Energy savings for electric lighting in the range of 20-60% are common.  Savings are very dependent on the nature of the light harvesting control system is deployed in, and its use.  Clearly, savings can only be increased in spaces with substantial daylight where electric lighting would have been otherwise used. Therefore, daylight harvesting works best in spaces with access to conventional gold clerestory windows , skylights , light tube groups, glass block walls, and other passive daylighting sources from sunlight; and where would it be necessary to leave the electricity supply? Such spaces have included offices , atria , interior public multistory plazas and short shopping mall , and schools .
It is too simplistic to try pour augmenter energy savings by Increasing the size of windows. Daylight over-illumination may cause glare for occupants, causing them to deploy blinds or other window shading devices, and compromising the daylight harvesting system. Even partially availed venetian blinds can cut energy savings in half. 
Impressive energy savings can not be realized in a system of design, calibration, or commissioning . Systems that dim or switch electrical lighting in a distracting manner, or that produce overall light levels that are perceived as too low, can be sabotaged by occupants.  (For example, simply taping over a sensor will create constant electric lighting at maximum output.)
The adoption of daylight harvesting technologies has been hampered by high costs and imperfect performance of technologies. However, studies have shown that by using daylight harvesting technologies, owners can see an average annual energy savings of 24%. 
TRACE 700 or (freeware) DOE-2, which considers thermal loads. 
Payback, and drivers for adoption
There is an incremental cost to daylight harvesting systems. Dividing this cost by the annual energy savings provides a “simple payback”, the number of years for the system to pay for itself.  The Calculated go short the payback period , the more it Likely Is That a building owner will invest in the system. Costs vary for a whole host of local factors, but if it is not expensive, the cost of the control hardware and installation falls, the payback period will be reduced.
The green building -sustainable building movement encourages sustainable architecture design and building practices. Various green building ecolabel certification marks exist around the world, Such As LEED , BOMA Best, BREEAM , HKBeam, and Green Star . All of These programs offer various items for building design features That Promote sustainability , and certification at various levels is Awarded for reaching a number of Given points. One of the main ways to gain points is through energy saving measures. Therefore, daylight harvesting is a common feature of green buildings.  Such green building practices are increasing the production of daylight harvesting components, leading to lower prices.
Many electric utilities provide financial incentives for their customers to save energy. One such incentive is rebates on daylight harvesting systems  , which also reduces payback periods.
In addition, energy codes and standards are beginning to address daylight harvesting. For example, the California Energy Title 24-2008 code recognizes primary and secondary daylight zones. At least 50% of the general lighting in areas must be controlled separately from other lighting. The code encourages automatic daylight harvesting in secondary areas by the power of adjustment adjustment that can be applied to the lighting design.  The 2009 International Energy Conservation Code (IECC) recognizes daylight zones around vertical fenestration and skylights, and requires that lighting in these areas be controlled separately from the general lighting in space. [ citation needed] The 2010 ASHRAE 90.1 energy standard, expected to be published in the fall 2010, est expected to address daylight harvesting. Meanwhile, ASHRAE 189.1, the first of a generation of sustainable construction codes, defines daylight zones and requires daylight harvesting control. [ quote needed ]
- Passive daylighting
- Active daylighting
- Sustainable architecture
- Sustainable design
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