Daylight (Illuminating with Skylight and Windows)

Written October 17, 2019

Daylight (Illuminating with Skylight and Windows) 

Daylight applications have been reintroduced in an attempt to design more energy-efficient lighting systems in office areas as well as production and manufacturing facilities. Careful analysis of architectural design should be made to determine the type of exposure, location and orientation of the area to be considered for skylights or supplemental window lighting.

Heat gain or heat loss due to windows or skylights versus the amount of light should be considered, as sunlight is generally not a stable light source for illumination or heating.  One interesting study of illumination, heat distribution & cooling is known as fenestration. It also encompasses arrangement, proportioning, and design of windows and doors in a building. The Fenestration Research Group at the Florida Solar Energy Center studies the energy and illumination performance of fenestration systems.

The main focus is on solar heat gain and its effects on the thermal performance of buildings and energy costs for heating and cooling. The use of windows for daylighting building interiors for visual comfort and savings on lighting energy use is also studied. Illumination Requirements 

To determine levels of illumination that are needed to perform a particular job; one will usually refer to a set of guidelines that are published by various agencies. The Illuminating Engineering Society, the most widely used source, has published recommendations that were based on an averaging of data and assumptions about user eyesight, age, task demand, etc., for determining illumination levels for the unique applications found under actual field conditions.

The recommendations are divided into seven ranges of illumination. The first three categories “A” through “C” are levels to be used over an entire area in which the visual task remains constant over time and space. Categories “D” through “F” involve tasks that remain relatively fixed at one location in the majority of work situations. The illumination of these task locations should be applied to the task areas only.

At the same time, a minimum of 20 fc (foot-candles) should be maintained in the non-task location. Category “G” is for extremely difficult visual tasks and may be difficult to illuminate properly. This extreme task will require a careful analysis of all considerations in order to arrive at a well-developed overall illumination system as well as a system for specific task illumination.