Daylighting
Last Update: November 8, 2010
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Electric Lighting Integration

The success of daylighting designs is intimately linked to the contribution of electric lighting designs, and vice versa. As daylighting-related decisions are being made from the early schematic design process through the completion of the architectural details, they become the context for electric lighting design.

During daytime, electric lighting must be integrated with daylighting to ensure adequate light levels for space activities without glare, i.e., required illuminance levels at points of interest and comfortable luminance distributions for key occupant locations and view directions. Electric lighting integration during daytime should be considered for the whole year and for different sky conditions to complement the varying daylighting distributions over the occupied times.

A key issue in integrating electric lighting with daylighting is the consideration of the Correlated Color Temperature (CCT). Unless significantly altered through spectrally selective glazings that reduce blue content, transmitted daylight has high color temperature. Light from blue sky can have significantly high CCT (reference daylight sources). Electric lighting with high CCT (higher than 4,100K) is a better match to daylighting. The selection of CCT can be based on the type and timing of space functions, leaning towards higher CCT for daytime activities. High CCT during nighttime, however, may not be preferable depending on space functions. Moreover, selection of CCT for electric lighting is a matter of preference and electric lighting design intent.

Successful daylight designs should result in glare free daylit spaces, minimizing the need for electric lighting during daylight hours. For more information on daylighting strategies and technologies please see section Daylighting Strategies. Unsuccessful daylight designs can be improved through electric lighting. Side-lit spaces with punched windows, high visible transmittance glazing, and low window-wall reflectance result in glare for view directions towards the window wall (see section Side-lighting). Electric lighting illuminating the darker wall surfaces between the punched windows can balance out the high contrast. Electric lighting can also be used to illuminate the upper walls at the back of a side-lit room to balance luminance distributions.

Electric Lighting Used to Balance Light
Electric Lighting Integration Figure 1.  Electric lighting used to balance light across the architectural space, with daylight contributing from the right and electric lighting contributing from the left. Image courtesy of Barbara Erwine.
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Energy Savings
Adjusting electric lighting intensity based on available daylight contributes not only to luminous comfort but also to energy savings and peak electricity demand reduction. The energy savings is the net effect of electric lighting savings and heating/cooling savings or penalties.
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Daylighting

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