Basics of Daylighting in a Green Environment
The use of natural sunlight, known as daylighting, to illuminate a building can save energy, reduce operating costs, create visual appeal, and enhance occupant health and productivity. The U.S. Green Building Council Leadership in Energy and Environmental Design (LEED™) rating system encourages the use of daylighting to achieve high performance buildings. This course provides an introduction to the use of daylighting in commercial spaces. The course objective is to show why daylighting should be considered, the basic guidelines of using daylighting and some words of caution when using certain daylighting techniques.

1.3 The 'Efficiency' Of Daylight

Efficacy is a measure of how well a light source converts 'watts in' to 'lumens (or light) out'. For electric lighting, 'watts in' refers to the electric power . For daylighting, 'watts in' refers to natural light. In either case virtually all of that energy is converted to heat at a rate of about 3.4 BTUs per watt.

The table below shows that daylighting, in all forms, compares well against electric lighting. It introduces less heat per lumen than most electric sources and can REDUCE the cooling loads in a building due to lighting. However (and it's a big however), this assumes the daylighting can be effectively distributed and fully utilized for illumination.

Efficacy of Light Sources

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