Daylighting is a strategy for using natural sunlight to illuminate the interiors of buildings in order to reduce energy costs. By controlling the admission of natural light into a building, daylighting can reduce as much as a third of total energy use. It also connects indoor and outdoor spaces, creating a more dynamic, comfortable, and productive environment for building occupants. Daylighting is a passive design strategy for energy efficiency. Passive strategies take advantage of elements such as a building’s location, local climate, and materials—they aim to reduce the load of active strategies like heating and cooling systems by identifying natural opportunities to save energy and keep operational costs down. Passive strategies can help to reduce a project’s front-end costs along with its ongoing heating, cooling, and lighting expenses.
The natural light that enters buildings is a mix of direct sunlight, diffused skylight, and reflected light that bounces off of the ground and other surfaces. Daylight is generally more luminous than artificial light, so it can be a viable, energy-saving replacement for electric light. But daylighting isn’t as simple as designing a building with lots of windows and skylights to let light in. A good daylighting strategy starts at a building’s design phase and integrates many different design approaches to make decisions about its form, orientation, size and placement of windows and skylights, lighting design, façade and roof surfaces, and more. It incorporates windows and skylights, shading devices, and interior design to maximize benefits from natural sunlight. And it should be used in tandem with a responsive lighting control system, which reduces electric lighting when there’s sufficient ambient light. Because most of these considerations tend to be integrated with building design, it can be difficult—and in some cases impossible—to retrofit a building for daylighting.
Windows and Glazings
Window placement is crucial—a poorly placed window can cause glare or too much direct sunlight in a workspace or living space (and in occupants’ eyes), or can also release too much or too little heat. Successful designs place windows based on cardinal directions rather than street-side appearance when possible. Ideally, a building should maximize southern and northern exposures and minimize eastern and western exposures. South-facing windows help to conserve heat in the winter when they admit more sunlight and keep it out in the summer when they receive less direct light. North-facing windows provide even, natural light, with little glare and hardly any heat absorption in the summer. Though windows facing east and west admit a lot of light during the morning and evening respectively, they’re more likely to cause glare, admit too much heat in the summer, and aren’t helpful for keeping heat in during the winter.
Even when windows are placed well, it’s important to have other strategies for reducing glare, light intensity, and excess contrasts. Shading devices like light shelves, louvers, overhangs, and grilles can help to keep heat out during the summer and in during the winter. And today, designers can find a wide selection of high-performance window glazings and advanced glass technologies that mitigate the impacts of glare, light, and heat. Glazings in a variety of tints and metallic and low-emissivity coatings can be manufactured and modified to maximize visible light and reduce thermal transmittance. Designers should also consider the reflectivity of interior finishes and partitions.
Since even high-performance window glazings do not insulate buildings as well as walls do, one of the biggest challenges of daylighting is finding the balance between letting light in and regulating indoor temperatures. Still, when compared to a typical window, high-performance glazing systems tend to let in more light and less heat, which has less of an effect on the building cooling load in the summer. Of course, there are different daylight and heating guidelines depending on a building’s location, and an office building in Helsinki will need a very different strategy than one in Sao Paolo. For more information about thermal performance in different climate zones, see the American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE)’s Standard 90.1 energy code—though it doesn’t cover daylight.
Certifications and Green Building Rating Systems
Passive House is a Germany-based building standard committed to passive design. During the winter, certified Passive Houses use the sun, internal heat sources, and heat recovery rather than traditional heating systems. In the summer, they use passive cooling techniques like strategic shading. Several green building rating systems, including LEED and Living Building Challenge, also offer points for daylighting.
Full-spectrum, natural light is a mood-booster. This is because sunlight stimulates more production of serotonin, a neurotransmitter responsible for lifting mood and improving cognition and memory. This can also enhance productivity in the workplace, reinforce circadian rhythms, and reduce symptoms of seasonal affective disorder. Plus, natural light is constantly changing in color and intensity, which provides building occupants with a greater sense of connection to the outdoors.