Defining Daylighting

Since the beginning of time, man has relied on the natural light of the sun as its main illumination source.  As a light source, the sun produces the right quality and spectrum of light that the human eye desires and the human brain requires for optimum performance during the day. It is a free source of light, many thousand times greater in intensity than is needed for different building uses.

But it is also a varying source of light that changes based on the date, time of the day and climatic conditions. These factors make the daylighting solution much greater than any one product.

It truly is a combined solution of daylighting, electric lighting and controls that produces optimal results. High-quality natural light should be captured, transported and diffused, all in conjunction with user-responsive lighting controls and high-performance electric lighting to maximize energy efficiency and visual acuity at the same time.

This combined daylighting solution needs to consider many factors for each application.  The primary consideration is building design — its location and how the space will be used.  With the layout and usage of the space in mind, you can then plan for your fenestration needs with vertical windows and potential toplighting applications.

Common Devices

Clerestories and skylights are two common rooftop devices.  Most multi-story buildings are limited to the effective use of vertical glazing options except upper level areas. Core daylighting of multi-building applications does exist and there is much research on the effective use of this strategy. However, a very small number of applications are in practice at this time.

Clear vertical glazing is used to increase views of the outside and thus increases human productivity. However, too much clear glazing can cause heavy contrast to the interior and requires additional light sources to offset the effect to the space. Instead, builders should combine clear line of site glazing with a diffused or light redirecting glazing section, or combine it with a reflective louver device.  These devices will drive down glare and can redirect light upward for indirect reflection — driving light deeper into a space.

On the Top

In low-rise buildings and top floors, the use of toplighting provides a very effective way to minimize total fenestration area needed to properly daylight the space. If you think about how we use electric lighting for building spaces, we utilize fixtures from above. Just like electric lighting, toplighting illuminates from above — think of skylights as a wireless light fixture.

The light produced from a toplighting device can provide three times the light of a vertical fenestration. Most designs require only 5 percent of the roof area or less to be covered by a toplighting device to properly light a space. This provides a much lower overall thermal impact to the building than utilizing 30 to 40 percent vertical wall applications to light the space found in contemporary daylighting design.

Toplighting daylighting delivery systems can help architects and contractors earn LEED and ENERGY STAR accreditation points across all commercial rating systems. The U.S. Green Building Council’s LEED rating system is internationally recognized. In each rating system, including a daylighting delivery system can earn anywhere from five to 30 LEED credits – putting a project well on its way to silver, gold or platinum status.

The Alliance to Save Energy analyzed the 2012 International Energy Conservation Code and concluded if all 50 states adopted the standard, the country could see $40 billion annual energy savings by 2030.  Daylight harvesting is required per section C405.2.2.3 of the standard. Lighting in day-lit zones of enclosed spaces must be controlled separately from general lighting in the space. Control zoning within these daylight zones is limited to 2,500 square feet per zone.

The Need for Electricity

It isn’t an “either/or” situation. One cannot solely rely on daylight. Electric light sources are necessary for the times of day and times of year where the sun cannot supply the space with ample light. Therefore, your energy code conscious, day-lit space needs high-quality lighting solutions.

Humans today are used to walking into a space and turning on a light switch. Even if enough daylight is coming in through a window or skylight, an occupant likely will not turn off or dim the electric light manually. Leaving on an electric light source with the use of daylighting devices, increases the thermal load of a building.

However, the properly designed daylighting solutions will minimize thermal impact and overall energy use. The daylighting components bring in natural light, and control the maintain optimum light levels and energy efficiency throughout a space. This is managed by incorporating the appropriate electric light levels where and when they are needed. The seamless integration of all three components reveals true energy savings.

The Lawrence Berkeley National Laboratory studied the effect of daylighting and daylighting controls on energy savings. They found the use of daylight harvesting can reduce energy consumption by up to 29 percent. And, to their best estimates, combining daylight harvesting, lighting controls and occupancy sensors can reduce energy consumption by up to 38 percent.

Energy codes worldwide are evolving to include daylighting mandates, but the goal of reduced energy consumption cannot be fully achieved by only adding daylighting or reducing electric energy use alone. Harnessing the ultimate power of the sun achieves a global goal to find sustainable and renewable energy.

Grant Grable is the vice president and managing director of global business development at Acuity Brands. Catherine Bruce is the marketing manager for Sunoptics. Grable can be reached at grant.grable@acuitybrands.com and Bruce can be contacted at Catherine.citroni@acuitybrands.com.

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