Use natural sunlight instead of electric lights as much as possible to illuminate rooms. It is free and the more it is used, the better the inhabitants feel and the less electricity they use.
There are two types of daylighting, direct sunlight that is warm and bright but it creates glare and dark shadows, and ambient sunlight that reflects off walls and floors with a more pleasant soft glow and no shadows. On cloudy days, all the interior natural light will be ambient.
On sunny days, the number of footcandles, the measurement of light falling on one square foot, is ten times as much as on a cloudy day. From one to ten percent of that light will enter a building, but that is plenty for most rooms. Kitchens and bathrooms may need as much as 80 fc, where hallways need only 10 fc and living rooms 10 to 20 fc.
Making the best use of daylight takes some careful planning but has many positive results:
- It saves energy and fossil fuel use. This even applies when the energy source is photovoltaic panels if electricity can be fed back to the grid.
- It saves money on utility costs as well as for replacing light bulbs.
- It saves natural resources used in creating light bulbs, lighting fixtures, and parts for solar system repairs.
- It helps heat rooms, but if not planned correctly can also require higher cooling costs. It can decrease cooling costs when used to vent heat through clerestory windows.
- It can be better for good eye health and makes it easier to read as people with cataracts will attest.
- It keeps the inhabitants better in touch with their natural environment–passing of clouds, falling rain or snow, warm sunlight or cold winds all connect people to the outside world both physically and emotionally.
- It helps prevent Seasonal Affective Disorder (SAD) in which people experience depression usually in shorter winter days from being deprived of hours of daylight.
- It increases productivity in work environments.
- School children in classrooms with daylighting have been shown to do better on standardized tests than students whose classrooms have minimal or no daylight.
Planning the best type of daylighting depends on the climate. In moderate regions, fewer windows should be located on the western side of the building and an overhang or awning should be used to keep out hot summer sun on south-facing sides. In hot, humid areas like Greenville, South Carolina and most of the Southeastern United States, exterior shades and vines can help keep direct sun off all of the windows. Clerestory windows high on the walls or skylights that open can draw hot air up and out of the house. Cross ventilation can be achieved by placing windows that open on two sides of the rooms.
In colder areas and in mountain homes in the Blue Ridge area above Greenville, windows on the north side should be kept to a minimum. They get little direct sunshine and lose more heat than they gain. The north light is ideal ambient light free from glare, so well-insulated, low-E coated windows with thermally resistant frames and argon gas insulation should be installed on that side to reduce heat loss.
All windows should be double-pane, low-e with a solar heat gain coefficient (SHGC) of 0.60 or higher so more solar heat will enter, and a U-factor of 0.35 or below to lower the heat flow and retain heat inside. Double-pane glass, which is two pieces of glass separated by a sealed air space, offers at least a double base R-value of single-pane glass.
There are also tripple-pane windows and coatings that reduce the amount of sunlight passing through the window, but this is a negative when using the windows for passive solar collection. A solution is to use the double-pane windows facing south, and place the higher R-value windows facing the other directions.
In all zones, light-colored interiors reflect light and make rooms brighter. Use clerestory windows, skylights, and tubular skylights to bring daylight in from above. Use glazed skylights to better diffuse the light. Place windows across from each other to balance the light and prevent glare. Keep west-facing windows to a minimum in all areas except cold ones to avoid heat from hot afternoon sun.
Watch the attached video of an ideal planned daylight home and someone please build a home like this in the Greenville area. It creates balanced glare-free light through amazing views to the outside, but also controls heat gain and loss and cross ventilation. Planning of a daylight home in urban areas involves securing privacy through frosted windows, landscaping, or use of shutters and curtains.
In addition to checking ENERGY STAR® labels for U-factor and SHGC, look for visible transmittance (VT) for the amount of visible light the glass transmits. VT is a number between 0 and 1, with 1 being the highest amount of light transmitted. Air leakage (AL) is the cubic feet of air through a square foot of the window area (cfm/sq. ft) with the lower number meaning the less air that will get through window assembly cracks. Condensation resistance (CR) measures resistance to forming condensation on the interior surface. A higher CR rating, expressed between 0 and 100, means the product is better at resisting condensation. The National Fenestration Rating Council (NFRC) label
is an excellent aid in energy efficiency comparison of windows.
Local stores that sell ENERGY STAR® windows, skylights, and window components in Greenville, South Carolina are:
- Pella Windowscaping Center, 864.297.1280, Garlington Road, Ste C, Greenville, SC 29615
- B&L Window Co., 864.232.1410, 7 W Stone Avenue, Greenville, SC 29609
- Champion of Greenville, 864.234.9500, 201 Forrester Dr., Bldg. C-5, Greenville, SC 29607
- Pacesetter Corporation, 864.288.0515, 120 Halton Rd., Suite 1, Greenville, SC 29607.