The importance of light in healthcare environments

Neesha Patel

Architect Mies van der Rohe stated: “The history of architecture is the history of man’s struggle for light, the history of the window.” However, in the rush to create commercially-viable and technologically advanced healthcare institutions, the importance of appropriate lighting has been forgotten and the cost of employing people outnumbers the cost of operating a lighting system by approximately 150 to one.

At the same time, the effect of light on our physiological systems cannot be denied; the human circadian pacemaker is extremely sensitive to dim light, with a light intensity equivalent to indoor room light able to significantly shift the timing of the circadian system. While the long term effects of inappropriate light exposure are under investigation, misalignment between the internal circadian pacemaker and the external environment is thought to contribute to health problems such as cardiovascular disease, diabetes, sleep and gastro-intestinal disorders.

The keynote speaker at the 5th Lighting Research Office (LRO) Symposium, Light and Human Health, Dr Mark Rea, said, “The last 25 years of research is now challenging our traditional definition of what constitutes ‘good lighting.’ Vision based lighting design neglects what recent research has found.” Simultaneously, the healthcare system is in a state of transformation; consumers have become increasingly health conscious and hospitals are beginning to take on the role of wellness centres.

Hospital complexes encompass numerous functional elements with the focus being self-sustenance. As hospital occupancy is constant, complex and dynamic, effective lighting is imperative and should be designed to meet the separate, and often conflicting visual needs of the staff, patients and visitors.

Current research has indicated that human physiology and behaviour are dominated by near-24 hour rhythms that have a major impact on our health and well-being. For example, sleep-wake cycles, alertness, performance patterns, core body temperature rhythms and the production of hormones such as melatonin and cortisol are regulated by an endogenous, near-24-hour oscillator in the suprachiasmatic nuclei (SCN) of the anterior hypothalamus. In order for the circadian pacemaker to ensure that physiology and behaviour are timed appropriately with the outside world, environmental time cues must be able to reset this internal clock.

The major environmental time cue able to reset these rhythms is the 24-hour light-dark cycle. The daily light-dark cycle resets the internal clock on a daily basis which in-turn resets the physiology and behaviour controlled by the clock. To our advantage, the visual and circadian systems operate at a different pace and can be simultaneously satisfied by the time factor; the visual system is instantaneous while the circadian system is slow to respond and both interface through perceptual constances. Properties of light that have been shown to relate to circadian resetting include the intensity, duration, pattern, timing of exposures, and more recently, the wavelength of light used.

The quantity of light is expressed in terms of luminance (lx). Daylight, at 10,000 lx, proves to be a good starting point as it is immediately recognisable. Natural light lifts spirits, makes spaces appear larger and reveals our world in true color. It forms an integral part of hospital building design as it provides variety and a link with the outside world on a temporal scale. The “time has come to accept bright light treatment into our therapeutic armamentarium,” urged Daniel F. Kripke, M.D., professor of psychiatry at the University of California San Diego.

In clinical practice, light therapy is commonly administered by means of a light box, a metal structure containing fluorescent tubes behind a plastic diffusing screen, at 10,000 lx. Bright light in the morning, resulting in the patient having to wake up earlier, has been documented as more successful than evening bright light for alleviating seasonal affected disorder (SAD) depression and insomnia. The biological mechanisms of SAD and light therapy are not clear, however, the rate of production of serotonin by the brain is directly related to the prevailing duration of bright sunlight and rises rapidly with increased luminosity. Research conducted by Eastman et al. regarding the adjustment of nurses and shift workers to a complete reversal of their normal working day by the use of timed exposure to 1200 lx and very dark glasses by day, remains the benchmark.

The study concluded that although 2500-10,000 lx received by the eye is the light level required to effectively combat SAD, depression and insomnia, the best light level for waking up and starting daily activities is 1200 lx or more; three times the light level to which most hospital areas are lit. Infact, most people spend their time indoors in environments with lighting between 50 and 500 lx. In the evening, the average living room is lit at 15 lx, but some people watch television in rooms as dim as 1 lx.

Another important aspect of healthy lighting is its timing, which determines whether light shifts the clock to an earlier time (advance) or a later time (delay). Under normal conditions, light exposure in the late evening delays the circadian system to a later phase and light in the early morning advances the circadian system to an earlier phase. This property of photic resetting is the underlying cause of sleep and other rhythmic disorders associated with ‘jet-lag’ and hospital shift work.

In 1985, original pioneers of bright light therapy discovered that the circadian system is the most sensitive to short wavelength light and has a spectral sensitivity different to that from conventional scotopic and photopic vision. These findings, and others in both animals and humans, suggest that a novel photoreception system exists in the eye that has evolved to detect light for the circadian system separate from that used for sight. Low light levels or monochromatic light was found to be just as effective for melatonin suppression (production of melatonin is inhibited by light) as bright polychromatic light. The logical conclusion is that the eye only utilises appropriate wavelengths in a chemical reaction so any white light; provided it contains the appropriate wavelength range; would work.

This led to the assumption that light at the bluer end of the spectrum that matched daylight was likely to be more effective for daytime background illumination than light at the yellow end. In a hospital setting, biorhythmic correction uses bright light within the range of 2500-10000 lx, to simulate an atmosphere of regular daylight, which is used to alleviate seasonal depression, increase length and quality of sleep, consolidate sleeping patterns in Alzheimer’s patients, improve performance of night-shift workers and regulate melatonin production. Psychological treatment uses colored and often kinetic light in the eye at far lower levels (namely 4-10 lx) to evoke reactions at a cellular level. The fourth dimension involves modulating monochromatic light to become a carrier in wavelength and frequency of exact electromagnetic information.

The correlation of light, melatonin regulation and its relevance to breast cancer has far-reaching implications for a 24-7 operation such as a hospital. Many theories have proposed that modern environmental causes such as electromagnetic fields or simple night-time light exposure increase the risk of breast cancer. This is true particularly if the night-time production of melatonin is interrupted, as melatonin has been shown to be part of the body’s natural defence against cancer. Taking such research into account, one can conclude that melatonin production will not be impaired when a room is in complete darkness or lit with the appropriate wavelength.

The suppression of melatonin in the daylight hours to signal to our bodies that we are biologically awake, and encourage its regular production in our sleep phase in relation to light (whether white, colored, coherent, incoherent or polarized), has formed the impetus of much of application of light to the body and subsequent physiological and psychological reactions. Ultra-weak emissions of light at 380nm are the conductors for the messages that control the cells’ reactions in organisms. More recent research has concluded that ‘messages’ are ‘sent’ at wavelengths ranging from 200-800nm; different wavelengths penetrate the body in different ways and promote unique reactions.

Photodynamic therapy, using monochromatic lasers, is used in conjunction with drugs to destroy or detect cancerous cells. Polarized light is used for skin disorders and to facilitate wound healing. Colored light (red and blue) on the skin can be used to heal recurring acne. Research by the Society of Dermatologists found that light, specifically monochromatic in wavelength, was more effective than drugs. Thus from a lighting design perspective, if colored lights are to be used indoors, color mixing is preferable over single filters, otherwise users of the space may suffer unexpected emotional reactions. At the forefront of molecular healing is Helionics Therapy using quantum physics to deliver electromagnetic radiation; the frequencies and spectral signatures are administered in the form of light, color and sound. Often the light is aimed at the chakra points on the back and can be used to treat current problems or more importantly, as preventive therapy.

As more is learned about the properties of light exposure that affect the visual and circadian system, such information can be used to optimize light exposure regimes to ensure proper synchronization.

These regimes can be used to reset the pacemaker after extreme de-synchronization, such as long-haul and space flights, the transition of shift workers, or to correct possibly damaging misalignment such as ageing or diurnal preference. In conjunction with parallel advances in understanding how light affects the pacemaker at a molecular level, physiological studies can be used to develop and optimize therapies to treat clinical disorders. In the words of A. Cornelius Celsus, a Roman medical writer: “Live in rooms full of light. Avoid heavy food. Be moderate in the drinking of wine. Take massage, baths, exercise, and gymnastics.”