] proposed, based on theoretical knowledge about how light impacts aging vision, circadian and perceptual systems, a 24-hour lighting scheme that is designed to provide: a) high circadian stimulation during the day and low circadian stimulation at night, b) good visual conditions during waking hours, and c) nightlights that are safe and minimize sleep disruption. It was proposed that high circadian stimulation be provided by 1000 lux or higher at the cornea from a circadian-effective white light source for at least 2 hours during the day. If longer exposures of light are planned, light levels may be reduced to no less than 600 lux at the cornea from the same circadian-effective white light source. No more than 60 lux at the cornea of a circadian-ineffective white light source (e.g., 2700K compact fluorescent lamp or LEDs) is recommended for general lighting in the evening hours.
Although the exact amount of light needed to impact the circadian systems of those with ADRD is not known, it is possible to theoretically compare a variety of practical light sources in terms of their ability to provide a criterion response by the circadian system (50% nocturnal melatonin suppression) for a fixed, small pupil size (2.3 mm diameter), as shown in [66
]. It should also be noted that the relationship between melatonin suppression and consolidation of rest/activity rhythms remains unclear. Since commercially available light meters are always calibrated in terms of the photopic luminous efficiency function, the levels of photopic illuminance needed at the eye are used as the measure of the amount of light needed to reach the criterion response. It is worth noting that under natural viewing conditions, pupil size can be larger than 2.3 mm in diameter, so a lower level of illuminance would be needed to reach this criterion level of melatonin suppression. Generally then, for light sources providing the same photopic light level, the greater the proportion of short-wavelength (visible) radiation from the source, the more effective it will be for stimulating the human circadian system. More importantly, although there is no compelling reason to assume that acute melatonin suppression and phase shifting of the timing of the biological clock respond differently to a light stimulus, it is important to keep in mind that the calculations presented in are based on studies where only acute melatonin suppression was measured.
Table 2 Photopic illuminance to achieve 50% melatonin suppression. Several practical light sources with the required photopic illuminance (lux, or lm/m2) levels at the eye, having a fixed pupil diameter of 2.3 mm, for 50% nocturnal melatonin suppression after (more ...)
Further research should be conducted to determine minimum light levels needed to impact the circadian systems of those with ADRD and to verify how the estimations presented in affect rest/activity patterns in those with ADRD. More importantly, it is not known how light levels can be reduced with increased duration of exposure. It has been shown in a 2-week light treatment study that delivering 30 minutes of a bright white light (4200 lux) in the morning to memory-impaired older adults and their caregivers improved sleep and mood in caregivers, but diminished sleep in those with memory impairment [67
]. It has been suggested that light therapy’s effect on sleep in those with ADRD is only measurable after 6 months of treatment possibly because these patients are slower to respond to the stimulus [43
Daylight from windows and clerestories is a circadian-effective light source, but, it should not be assumed that there will always be enough circadian stimulation from daylight in architectural spaces [68
]. Daylight levels in the room drop quickly as the distance from the window increases; 3–4 meters away from a window, daylight levels are quite low, even on a sunny day. It should be noted too that if sunlight from the window penetrates the room, discomfort glare will cause occupants to draw blinds or shades, eliminating daylight entirely from the space.
If energy consumption is a constraint, the architect can either select specific spaces to implement the proposed lighting scheme or follow a scheme similar to the one used in the experiments by Figueiro et al. [44
] by providing another layer of blue light in the morning. Portable luminaires providing diffuse blue light from LEDs (λmax
= 470 nm) can be placed on dining tables, around television screens, or attached to wheelchairs. It is not known, however, how successful compliance with these light delivery methods will be and how acceptable this kind of light source will be to users.
Good visual conditions for waking hours can be provided by lighting that is high, on the task, glare-free with no direct or reflected view of the light source, with softer shadows throughout the space, with balanced illuminance levels, and with good color rendering characteristics [69
Just as important, the proposed 24-hour lighting scheme should provide nightlights that reduce the risk of falls and help maintain sleep. Figueiro [65
] proposed the use of nightlights that provide visual information about the local environment (5 to 10 lux at the cornea) as well as perceptual information that enables the residents to orient [62
]. The proposed nightlights accent the rectilinear architectural features in the room as well as accentuate horizontal pathways to the bathroom. The use of motion sensors with dim nightlights eliminates the need to find switches in the dark and helps residents to remain asleep when caregivers enter the room. The use of low light levels allows older people to navigate through the space safely without disrupting their sleep. This proposed novel nightlighting system needs to be tested in persons with ADRD and installed in the field, but it has promising features to help reduce the risk of falls in those with ADRD.