Optimal daylight factor for energy-efficient toplighting system

Skylights can introduce considerable heat gain and loss that may offset the benefits of electric light savings and cause an increase in yearly net energy use. The design of a toplight system needs to take into consideration different toplighting types, including aperture size and orientation, electric lighting control, and, most importantly, the local climate.

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http://findarticles.com/p/articles/mi_m5PRC/is_2_112/?tag=content;col1