Daylighting Collaborative

Daylighting myths

Don’t let myths obscure your view. Learn how successful daylighting works today. See ten daylighting myths—unclouded.

what/why > what is daylighting?

Most simply, daylighting is the practice of using natural light to illuminate building spaces. Rather than relying solely on electric lighting during the day, daylighting brings indirect natural light into the building. Daylighting reduces the need for electric lighting and connects people to the outdoors. And it provides pleasing illumination at a fraction of the cost of the most efficient electric lights.

What is GOOD daylighting?

Good daylighting creates beautiful, appropriately lit spaces while saving energy. A successfully daylit building is the result of a combination of art and science, of architecture and engineering. It is the result of an integrated design process, and is not simply a technology that is installed once the building is complete.

The daylighting designers toolbox includes concepts of lighting power density (W/ft2), illuminance levels, contrast ratios, window to wall ratios, ceiling to skylight area percentages, and reduction in glare. However, we don't have prescribed values for these concepts that designers can use knowing they'll result in good daylighting. While there are efforts underway to establish metrics for good daylighting, they aren't available yet.

Even with proven metrics, daylighting will always be a mix of art and science, of logical thinking and common sense. Climate and geographical region, building type and use and building orientation are big factors in designing a successfully daylit building. Designers must always apply basic lighting and building performance principles to successfully employ daylighting.

Ten daylighting myths—unclouded

Don’t let myths obscure your view. Learn how successful daylighting works today.

Myth: Daylighting costs more.

Fact: Daylighting does not have to increase construction costs if it’s done using an integrated design approach. An integrated approach considers the effect of lighting on air conditioning.

The electric lights in modern buildings produce a lot of heat, while properly directed natural lighting generates almost no heat at all.

The decrease in internally generated heat allows designers to downsize the air conditioning system. The resulting cost reduction helps pay for daylighting improvements.

Myth: Daylighting is complicated.

Fact: It need not be. The Daylighting Collaborative has developed daylighting designs that work in most commercial and educational buildings.

These tried and tested designs need only be copied. Years of testing are built in and the improvements use readily available, off-the-shelf technology.

The result is reproducible energy savings and performance, minimal investment of design time and no risk. Copy rooms are available for schools, offices and manufacturing sites.

Myth: Daylighting lets in too much heat.

Fact: The light-to-heat ratio for daylighting is far better than even the most efficient electric lights.

Properly designed daylighting screens out 99 percent of the sun’s heat while providing 50 foot-candles of light, which is more than enough for most tasks.

Myth: Daylighting causes glare.

Fact: Glare happens when too much light enters a building. And this happens all the time in conventionally lit buildings (notice the drawn blinds in the windows of most office buildings).

A properly daylit building uses carefully placed windows, shading devices and low-transmittance glass—techniques that block direct sunlight and greatly reduce glare.

Myth: It's better to upgrade lighting and HVAC efficiency.

Fact: It’s better to reduce the need for electric lighting and cooling in the first place. Cool daylighting does both.

Natural light reduces the amount of installed electric lighting (within the limits of what’s needed for nighttime use).

Less electric lighting means less heat gain, which means less heat to remove with air conditioning, using less energy.

What lighting and cooling is left can then be done by the most efficient equipment available. Being efficient is always a good idea, but needing less energy is even better.

Myth: Daylit buildings need clear glass windows.

Fact: Clear glass windows let in too much light, far more than what’s needed for effective lighting.

The sun provides 7,000 to 10,000 foot-candles of light, while indoor office spaces need only about 50 foot-candles.

Too much light causes glare and the "cave effect", where the back of the room appears dark compared to other surfaces. This encourages people to close the blinds and turn on overhead lights to cut down the contrast in the room.

Well-designed daylighting lets in natural light that balances overhead electric lighting while curtailing glare.

Myth: Daylighting = skylighting.

Fact: Properly designed skylighting is a good technique in certain situations, such as enclosed hallways or very deep spaces. However, in many schools and offices, windows can provide most of the daylighting that’s needed.

It’s the placement and size of the windows that matters for effective daylighting. Clerestory windows—a row of small windows near the top of the wall—bring light in high in the room, producing a natural glow on the ceiling that mimics our experience of the sky.

Skylights aren’t usually needed to achieve good results until you get beyond 25 feet of the perimeter windows.

Myth: For daylighting to work you need sunny, clear days.

Fact: Even a completely overcast sky provides 5,000 to 6,000 foot-candles of illumination—a hundred times more light than needed for daylighting.

In some ways, overcast skies typical of northern climates provide a better lighting source because the light is more diffuse and even.

Daylighting is most challenging in the sunny climates of the south because of the immense amount of illumination from the sky and sun. This illumination must be reduced and carefully controlled.

Myth: There’s only one correct way to daylight.

Fact: Specific daylighting techniques vary, depending on location, number of building stories, building orientation and computer use in the building.

Daylighting techniques can be adapted to meet the needs of almost any building, whether it’s a warehouse, school, office, or government building.

Myth: Daylit buildings are all glass.

Fact: All-glass buildings don’t provide good daylighting because they get too hot and have massive problems with glare.

Windows constitute about 25–40 percent of the wall area of effectively designed daylit buildings. On average, window area in daylit buildings isn’t all that different than windowed area in non-daylit buildings.

Good daylighting technique depends on the proper placement of windows and performance characteristics such as visible light transmittance and solar heat gain coefficient—not having large amounts of glass.