by Jess Sharman
In architectural terms, ‘daylighting’ refers to using natural light to provide occupants with the level of lighting they need for essential activities. For a building to be considered ‘daylit’, the primary source of daytime illumination must be natural light.
There are a few practical reasons for designers to embrace designing for optimal use of natural light. This includes lessened artificial energy demands, resulting in lower operating costs; increased revenue, particularly in retail applications; and increased safety in public places. Studies show that using natural light in public and transportation buildings helps reduce possible threats to occupants and users. One of the most practical reasons, however, is the effect that natural light has on the humans who occupy the building; it is becoming increasingly apparent that humans are at their healthiest and most productive when they have adequate access to natural light.
Supporting the cycle
When it comes to the human element, the primary purpose of daylighting is to help support the circadian cycle, provided by the natural light and dark throughout the course of a day. Of course, the Earth’s natural lighting cycle can be unpredictable: solar position and weather conditions play a part in how much and what type of light/dark we receive. The cycle also depends on location –northern latitudes will not receive the same exposure to light as those living in southern ones, and vice versa re: dark. Yet, exposure to both light and dark in a natural, cyclical manner is imperative to human health.
When applied in architectural design, daylighting can be used as a way to mimic/take advantage of the natural cycle, thus achieving multiple human health benefits:
- Controlling body (circadian) rhythms, changes in core body temperature and hormone secretion. When we are in sync with the natural world’s lighting, we are healthier and sleep better.
- Positively affecting health and mood. Lack of light can contribute to depressive disorders. Various studies have shown that people with access to natural light and window views are happier, more productive, experience less sick time, and recover faster from illness when they do get sick.
- Enhancing learning, productivity, and brain performance. Research suggests that employees and students who work/learn in buildings with good natural lighting levels perform better, produce more, and have better attendance records.4
Doing it right
While the benefits of daylighting are plentiful, there are also adverse effects that need to be avoided. Improper installation of windows and daylighting structures can create an uncomfortable space; therefore, view window and daylighting aperture design and specification must avoid excessive glare and heat, carefully considering how best to achieve appropriate brightness levels and thermal comfort.
Passive solar design
Despite our understanding of the human need for natural light, for many building owners, the primary reason to consider daylighting remains the energy load reduction. Passive solar design combines daylighting and passive solar heating methods to aid in heating, cooling and lighting a building.
South-facing apertures collect solar energy, which is stored in high-heat capacity materials. Natural convection and radiation then distribute it into interior spaces. North-facing apertures provide additional natural light for illumination. To eliminate thermal comfort issues, design sun spaces to close off from the rest of the building and use filters and other design features to keep the building at a comfortable temperature. Apertures can also be designed to provide fresh air as/when weather conditions allow.
Direct vs diffused light
There are two types of natural light used in buildings:
Direct light – As the name implies, direct natural light passes through windows, doors and other apertures without hindrance or filtering. Because it passes through as a straight beam, direct lighting tends to provide the most intense light at its entry point, which lessens as you move further away. This can result in areas directly in the light’s path suffering from brightness, glare and thermal discomfort during intense sunlight, while unwanted shadows form in locations outside the light’s path. So, while direct lighting is beneficial in some situations, a different way of distributing daylight is required to achieve good ambient lighting (especially in larger spaces).
Diffused light – With diffused lighting, direct light beams are broken and dispersed as they pass through an aperture, providing more evenly distributed light across an area. As a result, the lighting is softer and more broadly spread, eliminating glare, reducing the risk of thermal discomfort, and removing shadows.
Types of glazing
There are various glass options to consider when designing for daylighting purposes: clear, modified composition (low iron [extra clear], body tinted), modified surface (fritting, applied film), coated, laminated, patterned, and mirrored. Nonglass products like layered polycarbonate, PVC and glass reinforced polyester (GRP) also work well for daylighting purposes.
One of the more common arguments against daylighting is concern about thermal comfort; intense natural light lets in too much heat. While it is a concern and careful consideration is necessary when designing and specifying, today’s daylighting methods are far better at addressing thermal comfort issues. Modern systems use filters to help retain temperature balance – stopping excessive heat from coming in during warmer times and preventing it from escaping during colder ones. Therefore, the argument against daylighting for thermal comfort reasons is weakened, and the benefits significantly outweigh the concerns.
Determining lighting levels
While BS 8206-2:2008 provides a measurement for determining appropriate lighting levels, research has shown that the issue is a bit more complex since its publication. For comfortable, fit-for-purpose lighting levels, daylighting factors should be assessed holistically: Where is the building located? What is the orientation of the front of the building? What is the interior space layout? What is the space used for? There are also aesthetics, visual comfort levels (avoiding dark patches and glare), seasonal, weather and daytime light changes, and energy implications to consider.
Apertures vs view windows
When designing for passive lighting, daylighting apertures should be considered separately from view windows. For optimal use of natural light, daylighting apertures need to be higher than viewing windows. Size and glazing requirements are also different.
- View windows should be clear and at a comfortable height for viewing from a sitting or standing position.
- Apertures should be specified to provide the space with sufficient diffused light.
- Shades, reflective surfaces, light shelves, and tinting can then be specified in correlation with both to eliminate glare and better redirect and distribute diffused light.
Because higher apertures generally provide the best natural illumination, designers often use roof lighting. There are a few different styles of roof lighting to consider, including clerestory, skylight, sawtooth, and monitor. Each type brings light into a space differently, depending upon the time of day and year. Consider environmental and maintenance factors when designing and specifying the roof lighting type.
Other uses for natural light
In addition to illumination and creating solar energy, natural light can be used in a building for other purposes. This includes:
Perception – Altering a person’s perception of space and shapes to create a pleasing illusion.
Focus – Directing attention towards or away from certain spatial elements.
Whatever style of daylighting aperture is selected, there are a few things to consider when designing for daylighting.
- Balancing thermal and lighting needs. Glazed openings create a thermal weak point, so assessing how much heat will be lost in cold months and admitted during warm ones is vital to create a balance between meeting lighting needs and thermal ones.
- UV protection and filtering. Some materials (paper, artwork, textiles, etc.) fade or deteriorate under certain light conditions, so buildings like exhibition halls, libraries, museums, and art galleries must take special care when determining daylighting levels and UV filtering.
- Minimizing noise pollution. Sound penetration levels must be factored in for buildings located in noisy areas or structures that produce a lot of noise internally.
- Wind exposure. As daylighting apertures tend to be higher in the building or on the roof, assessing things like maximum wind pressure and potential snowfall is essential.
- Atmospheric pollution. In high-pollution areas, horizontal and sloped apertures can quickly collect dirt and grime, reducing functionality. Because of this, these styles of daylighting apertures may require additional glazing and maintenance. The costs and effort of providing those things should be assessed for practicality.
- Safety and security. Considerations should take into account potential accidents and deliberate attacks.
Each year, on average, seven people die from falling through a fragile roof or roof light, while others suffer permanent injury.
Vertical glass located at walking level needs to be able to withstand the impact of someone accidentally running or walking into it. There is also a level of resistance to projectiles (stones, balls) that is necessary.
As for security, large panes of glass may draw vandals, and locking system options should be weighed according to need. Adding layers of shatter or blast proofing may be needed for facilities with higher safety or security demands. Depending on the level of security required, the result may be a compromise between security and ventilation.
- Frames/ support structures. The framing material specified influences the amount of light let in and how its distributed, so consider framing when determining expected performance.
A daylighting strategy is an integral part of the design of any building to be used or occupied by living beings. Research shows that workers and students are happier, healthier and better performers when sufficiently exposed to natural light. In healthcare buildings, natural light aids patients’ healing and recovery process. Daylighting also reduces a building’s energy load; in some cases, daylighting structures can produce energy themselves.
As with any sustainability feature, daylighting should be incorporated during the earliest planning and design stages. The best approach is holistic, factoring in building location and orientation, interior layout and purpose, aesthetics, visual and thermal comfort levels, seasonal, weather and daytime light changes, and energy implications. Additional considerations include security and safety, noise pollution and climate events, and cost and ease of maintenance.
Additional sustainability information and resources
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RIBA Plan of Work 2020 and the Sustainable Outcomes Guide
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