What is Daylighting?


Daylighting is the controlled admission of natural light -direct sunlight and diffuse skylight- into a building to reduce electric lighting and saving energy. By providing a direct link to the dynamic and perpetually evolving patterns of outdoor illumination, daylighting helps create a visually stimulating and productive environment for building occupants, while reducing as much as one-third of total building energy costs.

A daylighting system is comprised not just of daylight apertures, such as skylights and windows, but is coupled with a daylight-responsive lighting control system. When there is adequate ambient lighting provided from daylight alone, this system has the capability to reduce electric lighting power. Further, the fenestration, or location of windows in a building, must be designed in such a way as to avoid the admittance of direct sun on task surfaces or into occupants' eyes.

Alternatively, suitable glare remediation devices such as blinds or shades must be made available. The science of daylighting design is not just how to provide enough daylight to an occupied space, but how to do so without any undesirable side effects. Beyond adding windows or skylights to a space, it involves carefully balancing heat gain and loss, glare control, and variations in daylight availability. For example, successful daylighting designs will carefully consider the use of shading devices to reduce glare and excess contrast in the workspace. Additionally, window size and spacing, glass selection, the reflectance of interior finishes, and the location of any interior partitions must all be evaluated.

A daylighting system consists of systems, technologies, and architecture. While not all of these components are required for every daylighting system or design, one or more of the following are typically present:

- Daylight-optimized building footprint

- Climate-responsive window-to-wall area ratio

- High-performance glazing

- Daylighting-optimized fenestration design

- Skylights (passive or active)

- Tubular daylight devices

- Daylight redirection devices

- Solar shading devices

- Daylight-responsive electric lighting controls

- Daylight-optimized interior design (such as furniture design, space planning, and room surface finishes).

Since daylighting components are normally integrated with the original building design, it may not be possible to consider them for a retrofit project. (Source: WBDG)

Natural Light & Health

Light affects our bodies in two ways. In the first, light impinges on the retina of our eyes and, through our vision system, affects our metabolism and our endocrine and hormone systems. In the second, it interacts with our skin by way of photosynthesis and produces vitamin D. Most of our body’s life-sustaining functions are controlled by the hypothalamus, an area of the brain below the thalamus.

The hypothalamus is responsible for a number of metabolic processes and for such autonomic activities as energy and fluid balance, growth and Maturation, circulation, breathing, emotional balance, reproduction, heat regulation, and the circadian cycle. It links the nervous system to the endocrine system by synthesizing and secreting neurohormones as needed; these in turn control the secretion of hormones from the anterior pituitary gland.

Daylighting Strategies

Daylight has two components: sunlight, where the source is the sun, and skylight, where the source is the sky. Many but not all existing daylighting systems are designed to capture sunlight and admit it to the building. On a sunny day, as much as 100 000 lumen could be striking 1 m 2 of a building envelope, resulting in an illuminance of 100 000 lux. If the efficiency of the daylighting strategy were 100% that would be enough luminous energy to illuminate 100 m 2 at 1000 lux. The challenge in each daylighting strategy is to optimize the efficiency of the distribution system and, therefore, minimize the size of the collecting area. No daylighting system has 100% efficiency.

Therefore, the size of the collecting area is linearly proportional to the efficiency of the system. Daylighting strategies may be divided into two groups. The first includes sidelighting systems, where light is brought from the sides of a building into the interior space. A window is the simplest example of that strategy. The second group includes toplighting systems, where light is brought from the top of a building and distributed into the interior. A skylight is the simplest example of such a system. A successful daylighting strategy is one that maximizes daylight levels inside the building but optimizes the quality of the luminous environment for the occupants. Daylighting design is not only about maximizing light levels. Excessive sunlight in an interior can be extremely uncomfortable for its occupants. The key word in daylighting design is control, not only of light levels but also of the direction and the distribution of light.


Most sidelighting systems are designed to overcome the problem of uneven distribution of natural light resulting from the use of traditional side windows. Effective sidelighting systems operate by reducing excessive daylight levels near the windows and increasing them in areas away from the windows, thus giving rise to a more balanced daylight distribution throughout the room. Adding devices to the window glazing such as lightshelves, prisms or mirrored louvers offers a viable sidelighting strategy because of the ability of these devices to deflect light further away from the window wall and towards the back of the room.

Side window: include view and non-view elements, that is, windows and clerestory, respectively.

Clerestory system: also a side window but one that is placed high in the wall. It is usually contained

in a part of the building that rises clear of the roof.


Combined side-systems: include a side window and a clerestory provide a more balanced distribution of daylight than does a typical side window or a clerestory window alone.

Lightshelf system: A lightshelf is a device designed to capture daylight, particularly sunlight, and redirect it towards the back of the room by reflecting it off the ceiling.

Louver systems: Like most effective sidelighting systems, louver systems are designed to capture sunlight falling in the front of the room and redirect it towards the back, thereby increasing daylight levels in the back of the room and reducing them in the front.


Prismatic systems: designed to change the direction of incoming sunlight and redirect it by way of refraction and reflection.

Anidolic zenithal collector system: The zenithal anidolic system is comprised of two concentrating mirrors of parabolic shape that capture the incoming light flux over a wider area and distribute it inside a room.

Toplighting Systems

Skylight system: A skylight system is one of the simplest toplighting strategies. It usually provides a horizontal or slanted opening in the roof of a building and is designed to capture sunlight when the sun is high in the sky and diffuse light from the zenithal area of the sky vault, and introduce it into the portion of the room under the skylight. This daylighting approach can be used only for the top floor of a multi-story building or for single- story buildings. Several skylights uniformly Distributed across the ceiling lead to a uniform distribution of daylight.


Roof monitor and sawtooth systems: Roof monitors and sawtooth systems are toplighting strategies that differ primarily in their shapes. Under these systems, light is captured through vertical or sloped openings in the roof.

NASTARAN SHISHEGAR Architect,  lighting Specialist, Sustainability Expert. Video Mail: info@nastaran.net?subject=Contact Home Resume - Nastaran Shishegar