Daylight Harvesting — Make Sure You’re Seeing the Savings

Are we truly taking advantage of our oldest and most important natural resource – the sun?

The sun plays a major role in the design of most facilities. It can impact the orientation of the building as well as the design of the building envelope and windows. For lighting designers, it also impacts the control strategies needed to balance the natural light entering the building with the artificial lighting systems. Daylight harvesting systems are utilized to create this balance.

Although it varies from facility to facility, lighting accounts for approximately 20-30% of a building’s electricity consumption. This is a substantial number; and all buildings are required by energy codes to implement automatic lighting control features to minimize energy consumption in a building. Most new lighting control systems respond to occupancy and turn lights ‘on’ when people arrive, and ‘off’ when they leave. Over the past few years, the major energy codes (IECC, ASHRAE) now require automatic daylighting controls in addition to occupancy controls. Gone are the days of turning lights ‘on/off’ based on occupancy alone. Why turn these lights ‘on’ if there is already abundant natural light in the space? A daylight harvesting system with photo sensors will detect the amount natural light present in a space and adjust the artificial lighting levels accordingly, or switch the fixtures off completely if adequate natural light is present.

Daylight harvesting is not a new control strategy and, for many years, has been a good energy-saving practice. The benefits of daylight go beyond that of energy reduction and cost savings. Studies have shown that natural light enhances worker and student productivity, and creates a more relaxed atmosphere for all types of activities. The concept of lighting systems to harvest this daylight is simple – as more natural light enters a space, less electric light (and energy) is needed to illuminate a room. The implementation of this concept is, however, a bit more complex and is one that often leaves owners with a system that does not perform and save energy as was intended.

In order to make sure that you are seeing the best savings, daylighting systems need to be designed, installed, and operated properly.


A lighting control system design must be clearly defined on contract documents – drawings and specifications. Designers must locate/orient the needed devices properly on the plans and must clearly identify the intent of the system.


The construction team must properly install all components of the system per the contract documents and the manufacturer’s recommendations.


Once installed, a daylighting system should be tested for proper operation. This should include a commissioning process to validate the system is operating to its full energy saving potential. And, finally, the owner needs to be trained on the system’s features and proper use of the controls.

If you would like more information regarding daylight harvesting, or if you would like assistance with an upcoming project, please contact Yancy D. Unger, PE, LEED AP at or (717) 845-7654.