According to the US DOE’s Energy Information Administration, health care facilities account for 7% of electricity use by all commercial and institutional buildings. Additionally, lighting equipment represents as much as 42% of total electricity used in health care facilities. Despite the extraordinary costs associated with lighting systems, health care applications provide a unique set of challenges and opportunities, which given the lack of research funding, leaves a large separation between research and applied design. Despite the obvious benefits and in many cases unique, lighting practices implemented by health care providers and facility managers, these efforts and their related benefits largely go unmeasured. This has resulted in the general deficiency of quantified benefits of “good lighting” and limited design guidance with respect to both common and specialized health care environments.
For patient and health care professionals alike, patient experience, observation accuracy, procedure success, patient recovery and patient safety (slips, trips and falls, etc.) are of the utmost concern. Given the range in age of patients (newborn to geriatric), varying degree of patient mobility and duration of treatment and observation, lighting requirements vary greatly. Since the degree of difficulty and resulting implications of visual tasks performed by patients are in sharp contrast to those performed by health care professionals, an extreme level of flexibility and accommodation is often a priority. The shift away from monolithic hospital-centric campuses to an outpatient population-centric model is becoming evident. Some sources indicate that inpatient volumes are predicted to fall 5%, vs. 30% growth in outpatient volume. In recent years, the shift in the health care facility archetype has driven facility design away from predictable sterility and towards residential and hotel-like interiors for an increased degree of patient comfort. This not only provides an atmosphere of recovery for the patient, but promotes a greater degree of family member and caretaker comfort and involvement throughout the recovery process. This has not only been shown to improve patient recovery but also to reduce the demand on overextended health care practitioners and staff.
To this end, many lighting practitioners also strive to strike a reasonable balance between the introduction of daylight and artificial lighting equipment. Additionally, providing patients the ability to control or adapt patient room lighting through accessible lighting controls, many times directly from the patient's bed, has been shown to provide positive benefits to the health and wellbeing of patients and foster a sense of independence. It is important to point out that for some patients, the simple act of flipping a switch or pressing a button may be an immensely complicated endeavor. This makes the development of more advanced control systems using integrated technologies such as voice and gesture recognition very promising for disadvantaged patients. However, despite the understandable desire to promote patient-friendly interiors and access to lighting controls, these technologies can lead to reduced visual performance and visual fatigue for health practitioners if not implemented correctly.
How do patients respond to lighting?
The connection between light and human health may very well be irreducibly complex. Clearly, understanding how both patients and staff respond to lighting systems is critical. The human response to lighting can take many different forms and are immediately observable or may take some time. Examples of immediately observable responses may include: visual performance as a function at a fixed luminance level, during visual adaptation (accommodating a shift in luminance), spectral power distribution and flicker, etc. Other, more delayed responses include: circadian entrainment (sleep-wake cycles) due to the emission of and sensitivity to short-wavelength light produced by traditional and solid-state (LED) light sources. Theoretically, the use of contemporary blue-rich light sources, like LED, may work in concert with scheduled periods of darkness to promote a greater level of circadian health. LED technology may also uniquely enable an extraordinary degree of astronomical chromatic adaptation through the use of color-tunable systems, which can vary light spectrum to achieve a wide range of luminance, color temperature, hue and saturation.
While the physiological response to light is a non-learned and otherwise natural phenomenon, the implications may be greatest in health care applications. Given the generally compromised nature of patient health, the potentially unique patient requirements such as those suffering from conditions impacting memory, reasoning and behavior, the conventional disconnectedness from natural sunlight, the physical and mental duress placed on health care professionals and the critical nature of health care related tasks, it is easy to see how lighting can play a critical role.
The Paradigm of Spectrum and Intensity
Temporal and spatial fluctuations caused by large repetitive patterns in décor, varying in special frequency (influenced by color and contrast), and lighting (flicker – variations in luminance) are not found in the natural world under normal circumstances. Unfortunately, the human visual system hasn’t adapted to process this phenomenon and responds negatively to these conditions. However, providing daily patterns of varying degrees in luminance throughout the day (“light and dark”) has shown to positively influence the timely secretion of the hormone melatonin, support a more natural circadian cycle, and provide a degree of “normality” and sense of time to an otherwise abnormal illuminated environment.
While color temperature (CCT) selection for health care applications is a point of discussion within the lighting industry, color quality has also grown in significance. Color quality undisputedly influences aesthetics, way finding and the perception of safety though the appearance of people, places and objects. Without diminishing the significant role color quality has on the aforementioned areas, the role color quality has on patient observation and procedure accuracy may prove to be of greatest significance.
Today, the primary qualitative metric to measure a light source’s ability to reveal colors accurately in comparison to a “natural” light source is known as Color Rendering Index (CRI). CRI was covered recently in a previous article, titled “The Color and Quality of Light – How We Measure it, How We See it.” According to the Illuminating Engineering Society (IES), CRI is the “measure of the degree of color shift objects undergo when illuminated by the light source as compared with the color of those same objects when illuminated by a reference source, of comparable color temperature.” In other words, this quantitative measurement provides insight into a light sources’ ability to render the colors of objects accurately in comparison with a natural light source (or blackbody radiator); think incandescent lamp. To determine the CRI rating of a lamp source, a series of eight, sometimes fourteen, standard color samples are illuminated by a reference light source, having the maximum CRI score of 100. Numerically the highest possible score is 100; however some sources, specifically those that are monochromatic (ex: low pressure sodium), can actually score a negative value. It’s also important to point out that CRI does not directly indicate the apparent color of the light source. There are many instances where individuals may relate color appearance to color quality, such as in the case of light sources that have been described to provide a “daylight” appearance. These sources are generally much “cooler” in appearance, having a CCT at or greater than 5000-6500°K. Ironically, it’s exactly at these color temperatures where most common light sources struggle to provide the color quality which the name “daylight” would suggest. While measurements such as CCT and CRI continue to provide meaningful insight for lighting practitioners, there is much to be desired in terms of measuring and predicting color quality.
Additionally, the relevance (and accuracy) of legacy metrics used to describe color quality of contemporary light sources are continually being called into question, which has resulted in several competing metrics such as the color quality scale (CQS). While there are understandably many opinions on this issue, most informed lighting academics and professionals will agree that the evaluation of color quality will not be the result of a single metric.
Emerging Standards
In recent years, the Lighting Research Center at Rensselaer Polytechnic Institute has invested a considerable amount of time and attention to this issue and has become an authority on the matter. RPI’s findings have been well documented in an “ASSIST Recommends” publication titled “Light Source Color for Retail Merchandising.” As the name would suggest, the intent of this publication primarily addresses color quality in the context of merchandising and retail applications. RPI’s recommendation is organized into two issues: the first provides a background on CCT and CRI, including their advantages and drawbacks, and discusses how they may be augmented for better use in retail merchandising. The second issue recommends two-metric approaches for specifying light sources to achieve desired color appearance and good color rendering in retail applications.
The relevance of RPI’s recommendation to the health care industry is the common goal of providing an “optimal amount of color saturation, but without distortion.” Through this recommendation, RPI introduces Gamut Area (GA) and suggests that the use of both CRI and GA can more accurately predict color acceptance than a single metric. As a standalone value, gamut area is yet another measure of color rendering, which has been more commonly used for general lighting in Japan than in North America. Gamut is also widely used in the video display and printing industries. Gamut area is defined as the calculated area enclosed within a polygon consisting of three or more (typically eight for lighting applications) chromaticity coordinates in a given color space. For lighting applications, these chromaticity coordinates are typically the same used for the purposes of determining CRI. Generally speaking, the larger the gamut area (coverage area) within color space, the more saturated (or augmented) colors will appear. (Source: LRC)
Since it’s possible for high-gamut sources to provide low color fidelity, as is the case of many RGB, RGB+W and RGB+AW theatrical lighting systems, CRI is still needed as a companion metric. The research conducted by the LRC, across a range of “observers form different geographical origins, and for sources of warm and cool CCTs, different spectral makeup and light level(s)” concludes that a combination of high CRI (80-100) and high GAI (80-100) is recommended. Since the publication of this study, LED component manufacturers such as Xicato, Bridgelux and others have begun to advertise both CRI and GAI values for products intended for application where color discrimination and quality are of significance. While GAI is still a “young” metric for general lighting applications, understanding and support continues to grow. With respect to GAI, it is also important to note that light sources exceeding a GAI of 100 may provide an overtly saturated appearance on some objects. While this may be appealing for some commercial and retail applications, it’s undesirable in health care applications—a balance is needed.
Another metric, which has yet to be fully embraced by the North American lighting market, is the Cyanosis Observation Index (COI). The influence of COI was recently documented in an article titled “Lighting for clinical observation of cyanosis,” written by Neil A. Midolo, MIEAust, CPEng, MIES and Larissa Sergeyeva, GradIEAust was published in the Australian Hospital Engineer. “Clinical observation has always been an important part of medical diagnosis. One important aspect of clinical observation is the reliable detection of cyanosis, that is, the bluish discoloration in the skin and mucous membranes, which indicates that oxygen levels in the blood are dangerously depleted. While pulse oximeters are used in operating rooms and recovery areas, there are areas within hospitals where these are not universally used and there are some medical conditions, for example where patients have poor peripheral circulation, which can make their use unreliable. In these instances the ability of medical staff to reliably detect the onset of cyanosis by visual observation may be critical to a patient’s well being.”
A great responsibility
The indissoluble relationship between a light source’s spectrum and the visual observation of colors may very well reward light sources with broad blue content (ex: LED) and punish those sources with narrow coverage in the blue region. But it’s not all about blue. Light sources providing an appropriate amount of red emission, “particularly around 660 nm where the maximum difference in spectral transmittance between oxyhaemoglobin and reduced haemoglobin occurs” is also preferable. LED technology may be uniquely capable of enhancing the observation of cyanosis, given the broadband emission of blue and red colors as well as the generally continuous nature of spectral power distribution of 3000-3500°K LED light sources. The range of luminance varies greatly across health care applications. The appropriateness and range of luminance, color temperature and overall spectrum varies greatly across health care applications. Given the unique spectral makeup of contemporary LED sources, the color temperature recommendations may vary between sources (ex: LED vs. Fluorescent) for the same space. This may be due, in part, to the greater amount of short wavelength light emitted by LED sources as well as the relatively smooth and continuous (broadband) nature of LED spectral power distribution. The former seems to contribute to a cooler perceived apparent color, compared to the measured CCT. As an example, some lighting practitioners have begun to substitute 3500°K (85CRI) fluorescent with 3000°K (80-85CRI) LED. This is leading towards a general shift towards lower CCTs in commercial interior applications, where LED is being considered.
In conclusion, the scope and complexities related to lighting for health care applications are vast, and are far more than can be captured in this single document. An entire ecosystem of specialized medical and lighting equipment manufacturers exist to address issues such as equipment sensitivity (ex: MRI), sealed and containment luminaires, anti-microbial finishes, etc. Additionally, new and reoccurring questions continue to arise related to the optimal spectrum for hospitals, outpatient service buildings, operating rooms, and so on. Notwithstanding the obvious financial benefits of energy efficient LED lighting solutions, lighting impacts far more than direct operating costs. This means the paradigm of spectrum and control will continue to influence health care applications far into the future. Going forward, one thing is for sure - our ability to influence and control light has never been greater. However, the intrinsic value of control comes with a great responsibility to seek out and address opportunities related to lighting and human health. While there are many unknowns and the industry is still exploring the implications of lighting, the opportunities that exist in health care applications are vast and are primed for engagement.
Article from: http://www.hubbelllighting.com/company/illuminations/the-intersection-of-lighting-and-health-care/
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