Dr. Donald L. McEachron, Teaching Professor, School of Biomedical Engineering, Science and Health Systems, Drexel University

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Dr. Eugenia V. Ellis, Associate Professor, Architectural and Interior Design, Drexel University

Human beings are the result of biological evolution rather than engineering design. One result of this reality is that humans are dependent on a variety of internal biological rhythms to control and coordinate both physiological and behavioral activities. Organisms, exposed to powerful geophysical cycles for countless millennia, have evolved specific mechanisms to adapt both internally and externally to daily and seasonal environmental cycles. These mechanisms depend on slowly changing light cycles marking the solar day and photoperiod changes associated with the seasons. The implementation of artificial lighting has changed the environment to which humans are exposed, disrupting biological rhythms and degrading physiological and behavioral function. The elderly are particularly vulnerable to such disruptions. To counter this, LED lighting technology can be implemented to mimic aspects of the solar day and help synchronize rhythms in the elderly, promoting temporal hygiene and thus, health and well-being.

Biological rhythms are ubiquitous in living organisms having evolved to subserve a number of critical functions. Any complex, goal-oriented device, whether a computer, automobile or human being, must be able to schedule various activities so as to maximize output and minimize interference. Moreover, control systems involving negative feedback – common in biological systems – are inherently oscillatory. In addition, many biological activities are themselves rhythmic – cardiac function, respiration, walking, etc. – and it is natural to expect rhythmic control systems to have evolved to produce these oscillating outputs. Considering these factors in light of the mechanisms of biological evolution, it seems reasonable that living systems have evolved numerous oscillators and clocks to control both physiological and behavioral processes. In fact, it would not be incorrect to conclude that virtually every aspect of biological systems are rhythmic – from the many cycles per second (Hz) frequencies in nerve cells as reflected in the electroencephalogram (EEG) to the near second long cardiac cycle; from hourly pulses in the secretion of all hormones to 28 day menstrual cycles and even to seasonal rhythms in behavior and physiology (an example of the latter is the occurrence of seasonal affective disorder in humans which can manifest itself as a depression which begins in the fall, extends throughout the winter and spontaneously remits in the spring and summer). Thus, every living thing – including humans – consists of a bewildering multiplicity of rhythms and cycles, all of which must be kept in some kind of temporal order to ensure proper physiological and behavioral health.

How is this control achieved? In many organisms, including humans, temporal order is attained through the actions of a dominant clock tied to the daily cycle of light and dark. The extreme stability of the Earth’s rotation provided for the evolution of these so-called circadian (Latin ‘about a day’) pacemakers – self-sustaining oscillators whose frequency is close to 1 cycle every 24 hours. Close, but not identical. This is due to the fact that sunrise and sunset – the markers of the solar day – change across the seasons, requiring that the internal circadian clocks be periodically readjusted to match the external day/night cycle in a process called entrainment. The effects of light and dark on these circadian clocks are complex and the result of many millennia of evolution in the natural environment of day and night.

The modern urban environment represents a problem in that artificial lighting creates a bizarre and unpredictable set of stimuli to which the circadian clocks have difficulty adjusting, so much so that the American Medical Association in 2012 declared artificial lighting to be a public health problem. Shift work, which accentuates these kinds of lighting changes and thus generates circadian rhythm disruption, has been linked to a variety of physiological and behavioral issues, including gastrointestinal dysfunction, cardiovascular issues, sleep disorders, psychiatric complaints, cognitive deficits and certain types of cancer1,2,5,7-9,12-15, all of which have been verified to some extent in animal experiments10,11,16,17. Thus, circadian rhythm disruption is both dangerous and debilitating.

These issues become especially critical as human age. Experiments indicate that the master circadian pacemakers in mammals – a bilateral set of nuclei in the hypothalamus called the suprachiasmatic nuclei or SCN – become less coherent and powerful as the animals age. In effect, the clock function of the SCN becomes weaker, making older animals more prone to circadian rhythm dysfunction. Poor or inappropriate artificial lighting exacerbates the problem, augmenting the magnitude of any circadian disruption and significantly reducing internal temporal order.

At the moment, there is no effective way to reverse these physiological changes in the SCN directly. However, there are ways to overcome some of the loss and help to maintain circadian rhythms and the internal temporal order these rhythms sustain. Improper artificial lighting may be part of the problem, but with new technology and proper planning and implementation, artificial lighting can become a significant part of the solution.

In the environment to which human ancestors were exposed, light could be expected to display a gradual increase in lighting (sunrise) and powerful, sustained illumination (daylight) and a gradual decrease in lighting (sunset) followed by a profound darkness (night). These effects involve both intensity and wavelength variations in perceived lighting. Focusing on illuminance alone, a moonless overcast night may provide only about 10-4 lux, while full daylight provides 10,000-25,000 lux and direct sunlight 32,000–130,000 lux. The actual levels depend on both latitudinal location on the Earth and weather conditions, but clearly the circadian system evolved to expect a dynamic range of lighting over some 6-9 orders of magnitude.

Compare this evolutionary expectation with modern nursing home realities. In one study, Ancoli-Israel3 reported that nursing home residents experienced an average of 9 minutes of light over 1000 lux per 24-hour day. In another report, sixty–six institutionalized elderly were monitored for a three-day period. The mean lighting exposure was a mere 54 lux with only 10.5 minutes of exposure over 1000 lux19. In a survey of 53 nursing homes, illumination was considered barely sufficient or inadequate in 45% of the hallways, 17% of the activity areas and 51% of the residents’ rooms20 in 4. It is little wonder that sleep problems and disorders are often reported for nursing home residents, even when such problems were not evident prior to admission6,18.

In order to provide a more naturalistic lighting cycle, we are developing a solar day mimicking, energy-conserving integrated light-emitting diode (LED) luminaire for commercial and residential use. This system will provide a gradual onset (sunrise) and offset (sunset) in light intensity with the appropriate wavelength to ensure entrainment of circadian rhythms. Light during ‘night’ will be shifted towards red wavelengths, since human circadian clocks show little or no sensitivity to such wavelengths while people can still see and maneuver effectively in their environment.


1)    Akerstadt, T. and Gillberg, M. (1981). Sleep disturbance and shift work. In Reinberg, A., Vieux, N. and Andlauer, P. (eds.) Advances in the Biosciences, Vol. 30: Night and Shift Work Biological and Social Aspects. Pergamon Press: Oxford, Eng., pp. 127-137.

2)    Akerstadt, T. and Torsvall, L. (1980). Age, sleep, and adjustment to shift work. In Koella, W.P. (ed.) Sleep 1980. S. Karger: Basel, pp. 190-195.

3)    Ancoli-Israel, S., Klauber, M.R., Jones, D.W., Kripke, D.F., Martin, J., Mason, W., Horenczyk, P., and Fell, R. Variations in circadian rhythms of activity, sleep and light exposure related to dementia in nursing-home patients. Sleep 20,1 (1997), 18-23.

4)    Berson, D.M., Dunn, F.A., Takao. Phototransduction by retinal ganglion cells that set the circadian clock. Science 295, (2002), 1070-1073.

5)    Caruso, C.C., Lusk, S.L. and Gillespie, B.W. (2004). Relationship of work schedules to gastrointestinal diagnoses, symptoms, and medication use in auto factory workers. American Journal of Industrial Medicine 46(6): 586-598.

6)    Clapin-French, E. (1986). Sleep patterns of aged persons in long-term care facilities. Journal of Advanced Nursing 11,1 (1986), 57-66.

7)    Davis, S. and Mirick, D.K. (2006). Circadian disruption, shift work and the risk of cancer: a summary of the evidence and studies in Seattle. Cancer Causes and Control 17: 539-545.

8)    Davis, S., Mirick, D.K. and Stevens, R.G. (2001) Night shift work, light at night and risk of breast cancer. Journal of the National Cancer Institute 93(20): 1557-1562.

9)    Fido, A. and Ghali, A. (2008). Detrimental effects of variable work shifts on quality of sleep, general health and work performance. Medical Principles and Practice 17 (6): 453-457.

10) Filipski, E., Delaunay, F., King, V.M., Wu, M.-W., Claustrat, B., Grechez-Cassiau, A., Guettier, C., Hastings, M.H. and Levi, F. (2004). Effects of chronic jet lag on tumor progression in mice. Cancer Research 64: 7879-7885.

11) Filipski, E., King, V.M., Li, XM., Mormont, M.-C., Claustrat, B., Hastings, M. and Levi, F. (2003). Disruption of circadian coordination accelerates malignant growth in mice. Pathologie Biologie 51(4): 216-219.

12) Ghiasvand, M., Heshmat, R., Golpira, R., Haghpanah, V., Soleimani, A., Shoushtarizadeh, P., Tavangar, S.M. and Larijani, B. (2006). Shift work and the risk of lipid disorders: A cross-sectional study. Lipids in Health and Disease 5:9 (

13) Knutsson, A., Hallquist, J., Reuterwall, C., Theorell, T. and Akerstadt, T. (1999). Shiftwork and myocardial infarction: a case-control study. Occupational and Environmental Medicine 56: 46-50.

14) Knuttson, A. (2003). Health disorders of shift workers. Occupational Medicine 53: 103-108.

15) Koller, M., Haider, M. Kundi, M. Cervinka, R. Katschig, H. and Kufferle, B. (1981). Possible relations of irregular working hours to psychiatric psychosomatic disorders. In Reinberg, A., Vieux, N. and Andlauer, P. (eds.) Advances in the Biosciences, Vol. 30: Night and Shift Work Biological and Social Aspects. Pergamon Press: Oxford, Eng., pp. 465-472.

16) Larsen, K.R., Barattini, P., Dayton, M.T. and Moore, J.G. (1994). Effects of constant light on rhythmic gastric function in fasting rats. Digestive Diseases and Sciences 39(4): 678-688.

17) Penev, P., Kolker, D., Ze, P. and Turek, F. (1998). Chronic circadian desynchronization decreases the survival of animals with cardiomyopathic heart disease. American Journal of Physiology 275(6 pt. 2): H2334-H2337.

18) Regestein, Q.R. and Morris, J. (1987) Daily sleep patterns observed among institutionalized elderly residents. Journal of the American Geriatric Society 35,8 (1897), 767-772.

19) Shochat, T., Martin, J., Marler, M., Ancoli-Israel, S. Illumination levels in nursing home patients: Effects on sleep and activity rhythms. Journal of Sleep Research 9, (2000), 373-379.

20) Slone, P.D., Mitchell, C.M., Calkin, M., Zimmermann, S. Lighting and noise levels in Alzheimer’s Research and Practice in Alzheimer’s Disease, Vol. 4, 2000

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