Bringing daylight into the home is very important. As our eyes age, less light actually gets to the retina to stimulate the nerves, therefore, more light (without glare) is required. The intensity of daylight is much greater than typical electric lights and daylight includes the full color spectrum. Furthermore, as natural daylight is free, there are significant economic and physical reasons to include the principles of "daylighting design" into your home.
Appropriate design criteria will vary depending upon your geographic location so it is best to contact a local lighting designer or architect who specializes in "daylighting design".
The most successful solutions bring the daylight into a space above the field of view through diffused glazing material. Rays of sunlight through clear glass or plastic can produce both unwanted glare and shadows.
Older eyes benefit from the increased quantity and quality of light
Ambient (general) illumination should be about three to four times higher than is typical for young people. 30 footcandles is recommended for general room lighting. Light levels should be adjustable by switching on a dimmer to allow adjustments according to the seasons and time of day. Bedroom and bathroom areas should have separate lighting for day and night; high during the day and low at night. Every room, including the living room and family room, should have built-in lighting with control switches at each location where people enter or exit a room. Motion sensors may be used so that lights come on only when rooms are occupied. Table and floor lamps should be used in combination with built-in general illumination.
Quality of Light
- Light levels that are adequate for the visual task
- Glare avoidance (direct and reflected)
- Uniformity in general lighting (with areas of interest that are not dramatically different)
- Orientation of lighting to the visual task
- Reduction of visual busyness
- Good color rendering
- Location and directional considerations to prevent accidents
- Balanced daylight and interior ambient light.
- Walls and floor areas evenly illuminated
As we age, our eyes become much more sensitive to glare. The highest rate of increased glare sensitivity occurs after the age of sixty. There are two types of glare: 1) direct glare, bright light from a fixture or bright sunlight streaming into a dimly lit room; and 2) reflected glare, strong light that bounces of a smooth shiny surface.
Avoiding Direct Glare
The best way to avoid direct glare is to utilize indirect lighting. This is accomplished by using a concealed light source where light is directed toward a ceiling or wall and reflected back into the room. It is important that the surface of the ceiling or wall be a matte finish and light in color. Exposed bulbs such as the tiny lights on a chandelier will produce direct glare and should be fitted with a translucent shade. Sheer draperies or woven shades should be used to minimize the glare and yet allow daylight into the room.
Avoiding Reflective Glare
Problem areas include glass-top tables, highly polished floors and/or counters and light-colored sidewalks. Reflected glare can be avoided by using materials with a matte finish or colors with a medium value. However, the kitchen presents a real challenge at the sink and the stove. Porcelain reflects less glare than stainless steel, but these surfaces are not trouble free. Rubber mats in the sink will help to reduce some of the problem.
Consideration should be given to increased light levels in areas for reading, hobbies, and daily activities. In the kitchen, lights located under the upper cabinets are essential for providing light on the work surface. For vanities, fixtures located on each side of the mirror that illuminate both sides of the face for shaving and applying make-up are important. Closet areas require light that does not alter the color of the clothing and is sufficient to distinguish dark colors (i.e. navy and black). Light sources have a color rendering index (CRI) which rates them on a percentage scale (high numbers being the best) for how true a color will appear under that light source. Sources rated 80 or above are recommended.
Lighting can also improve your general health
In addition to providing light for vision, the photobiological effects of light are very important for the health of older people.
Sunlight on the skin produces vitamin D, which is required for calcium to be absorbed and keep bones strong. One study of older persons living at home found that 54% had low vitamin D levels (Gloth FM, et al. Vitamin D deficiency in homebound elderly persons JAMA 1995; 274:1683-6).
Daylight through the eyes keeps our body clock (circadian rhythm) synchronized with the day/night cycle of light. Circadian rhythm disruption impacts both sleep at night and alertness during the day. A high percentage of older people experience sleep disorders due in part to lack of daylight.
Sunlight on the Skin
Calcium and vitamin D are essential to maintaining healthy bones through out life. Osteoporosis, the most common disease of the bones, characterized by a decrease in bone mass and density, is often called the silent epidemic. Worldwide osteoporosis afflicts an estimated one-third of women aged 60 to 70, and two-thirds of women aged 80 or older. Vitamin D deficiency can be prevented by sun exposure. A Japanese study of 258 stroke patients 65+ years old, half of which were exposed to sunlight on their face and hands for 15 minutes per day for a year, and half (control group) of whom maintained their normal activities without any specific activity for sunlight exposure, found that hip fractures significantly decreased by 84% in the sunlight-exposed group. Also, bone mineral density increased by 3.1% in the sunlight-exposed group, and decreased 3.3% in the control group (Sato Y, Metoki N, Iwamoto J and Satoh K. Amelioration of osteoporosis and hypovitaminosis D by sunlight exposure in stroke patients. Neurology 2003; 61:338-342). Most window glass blocks the ultraviolet light need for vitamin D synthesis, so plan to go outdoors without sunscreen, make-up, or lotions which might include sunscreen, for 15 minutes per day exposing the face and hands. It is best to avoid the two hours before or after 12:00 noon.
Light Through the Eyes
Recent discoveries of the specific cells in the retina of the eye that relay information to our body clock and the particular wavelength (similar to the blue sky) to which these cell are most sensitive reinforces the recommendation for including daylight within homes and encouraging people to spend time outdoors.
For more specific information about making lighting modifications to an existing residence, please go to: Lighting Your Way to Better Vision.
For more information about Light for Health, please
review "Proceedings of the 2nd CIE expert Symposium on Light and Health." http://www.cie.co.at/index_ie.html