After age 40, changes to the aging eye become more noticeable as visual capabilities decrease. The inability to focus on objects at close distances is noticed in particular after age 45; this is called presbyopia. As one grows older, less light reaches the back of the eyes because the pupil gets smaller and the crystalline lens inside the eye becomes thicker, absorbing more light. A 60-year old receives about 1/3 as much light at the retina as a 20-year old. The lens also begins to scatter more light as one ages, adding a “luminous veil” over images on the retina, which reduces the distinctness (or contrast) of objects and the vividness of colors. After age 60-65 years, chances of having age-related eye diseases are greater. Common age-related problems are cataracts, macular degeneration, diabetic retinopathy, and glaucoma. Cataracts are dark, cloudy, or opaque areas in parts or all of the crystalline lens. Macular degeneration refers to neural damage to central vision. Diabetic retinopathy occurs when blood vessels feeding the retina are damaged and regions of visual field are lost. Glaucoma is a result of too much fluid pressure inside the eye, which cuts off of blood flow and, thus, nutrition to the retina and ultimately the optic nerve.
As one ages, changes to the circadian system are also more noticeable and may lead to sleep disturbances. Surveys indicate that 40-70 percent of the oldest members of the population (over 65 years old) suffer from chronic sleep disturbances.21 In general, older adults tend to go to bed earlier in the evening and wake earlier in the morning than younger adults. Frequent nocturnal awakenings, difficulty falling asleep, and an increased number of naps during the day are also more common in the oldest adults. Sleep disturbances are associated with decreased physical health, including increased cardiovascular problems, disruption of endocrine functions, and decline of immune functions.22
Many physiological changes are implicated in the circadian rhythm disturbances found in older adults. Studies have shown that the SCN may become less responsive as we age. Studies have also demonstrated that changes in the amplitude and timing of melatonin and core body temperature rhythms may occur in older adults. Also, the first stage of phototransduction (when light signals are converted into neural signals) is negatively affected; older adults not only have reduced optical transmission at short wavelengths, which is maximally effective for the circadian system, but many typically lead a more sedentary indoor lifestyle, with less access to bright light during the day. In fact, research has demonstrated that middle-aged adults are exposed to approximately 58 minutes of light above 1000 lux at the eye per day, while older adults in assisted living facilities are exposed to light above 1000 lux at the eye for only 35 minutes a day.23 Moreover, adults in nursing homes see as little as 2 minutes of light a day above 2000 lux at the eye.24
Previous research demonstrated that light can be used as a non-pharmacological tool to help older adults, including those with Alzheimer’s disease (AD), sleep more efficiently. Light in the evening can delay the circadian clock and help older adults sleep better at night and be more awake during the day.25 Other studies have shown that exposure to bright white light improved sleep efficiency of institutionalized older adults.26-28 Exposure to bright light (at least 2500 lux and as high as 8000 lux) for at least one hour in the morning for a period of at least two weeks consolidated sleep of AD patients; greater sleep efficiency at night decreased sleep during daytime hours and, in some cases, reduced agitation behavior.27, 29-33 Unattended exposure to bright white light (1136 lux average at the eye) during the entire day improved rest/activity of AD patients.7 Evening exposure to bright white light (1500 to 2000 lux) for two hours decreased nocturnal activity and severity of evening agitation (sundowning) of AD patients.26 Evening exposure to 30 lux at the eye of blue light from LEDs peaking at 470 nm for two hours consolidated rest-activity rhythms and increased sleep efficiency of persons with AD.8, 34 Figueiro et al. recently showed that a 24-hour “tailored” lighting system could improve sleep, depression, and agitation in this population.9
The visual system plays an important role in postural control and stability. Visual information is integrated with input from the vestibular and somatosensory systems, which are linked to balance control. Any changes that occur to any of these systems will affect the other systems’ capabilities of maintaining balance.35 In fact, studies have demonstrated that removal of visual cues by closing the eyes has been shown to result in increased body sway. Figueiro and colleagues showed that nightlights that provide horizontal and vertical perceptual cues are well accepted by caregivers and, more importantly, can help increase postural stability when older adults are transitioning from sitting to a standing position.36
Although not everything is known about the effects of light on health and wellbeing, with the information available today it seems reasonable to provide a 24-hour lighting scheme that maintains circadian entrainment as much as possible while promoting good visibility during waking hours and safe navigation at night.36 Following this logic, lighting in assisted living facilities and nursing homes should provide high circadian light stimulation during the day and low circadian stimulation at night, good visual performance (e.g., reading) during waking hours, and low-level nightlights that enable safe movement through the space and minimize sleep disruption.