Are rectangular or tubular skylights better for more natural light and energy savings?
Although the amount of electricity used for lighting in a house is only a fraction of what is used for heating, cooling and water heating, it still constitutes a significant annual cost. Using more natural light instead of lightbulbs is not a difficult task.
If saving electricity is your primary concern, replacing all your lightbulbs with LEDs is a less expensive option than installing either a typical or tubular skylight. Although not as natural as true sunlight, higher temperature bulbs—rated at 4000+ degrees Kelvin—produce a more natural, whiter light. Bulbs with a high color rendition index make colors looks more realistic.
Most people’s vision is better under natural lighting—even at a somewhat lower brightness level—than under typical artificial lighting. I can read a magazine easier by a window even on a cloudy day. Some businesses now use special lights that closely simulate natural light. They can reduce bulb wattages by more than 15% for big savings, and the workers cannot tell the light is dimmer.
A tubular skylight is generally a more efficient and less expensive choice than a traditional rectangular skylight. A traditional skylight provides more lighting and a view of the sky, but it creates a large hole in the insulation envelope of your roof and loses energy.
I installed a tubular skylight in my garage. It provides adequate light for most activities during the daytime. When there is a full moon, it produces enough light for me to walk to my car in the garage without switching on the light.
Tubular skylights are available in several diameters, depending on how much light you need and the space available. As a reference, a 10-inch-diameter model produces as much light as three 100-watt incandescent lightbulbs. A 14-inch model is equivalent to using five 100-watt bulbs.
If you are still using incandescent bulbs, the annual electricity savings from installing a large tubular skylight is about $90. If you typically use compact fluorescent bulbs or LEDs, the annual savings is about $20. This might not sound like a lot, but the tubular skylight should last for many years.
A tubular skylight requires no maintenance other than wiping off the glass or globe in the home. The dome on the roof should stay clean from the rain. It is not difficult to install one yourself, especially if you have an asphalt shingle roof.
Tubular skylights use a sheet metal tube that extends from above the roof to the ceiling below. The interior of the sheet metal has a reflective coating, so little brightness is lost as the sunlight bounces back and forth on its way down. A clear dome seals the top of the tube above the roof and a flat diffuser snaps over the bottom in the ceiling.
To control the brightness, optional dimmer flappers are available to reduce light intensity. These can be operated by an electric motor or a solar panel with a remote control. Another nice feature for bathrooms is a model that also works as an exhaust fan.
Most natural light comes in through windows. If you have relatively efficient windows, open the curtains or use just sheers during the daytime to allow light in. If you have old single-pane windows, use insulating shades. Opening them loses more energy than you save on lighting. Prune back shrubs that have grown up and block the window.
Placing decorative mirrors opposite windows can be effective. One method uses mirrors on opposite walls. This reflects light, and the repeating images in the mirrors add a sense of depth to the room. For a window near a corner, place the mirror on the adjacent wall close to the window. It will reflect the light out at 90 degrees from the window to brighten the entire room.