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Over-illumination is the presence of lighting intensity (illuminance) beyond that required for a specified activity. Over-illumination was commonly ignored between 1950 and 1995, especially in office and retail environments; only since then has the interior design community begun to reconsider this practice.
The concept of over-illumination encompasses two separate but related concerns:
- Use of more artificial illumination than required is expensive and energy-intensive. This includes consideration both of the appropriate level of illumination when spaces are in use, and when they are unoccupied.
- Some people find excessive levels of artificial light to be irritating, and some studies have shown that they may lead to adverse health effects. These effects may depend on the spectra of the light rather than or as well as the overall illuminance.
Since lighting accounts for twenty to forty percent of commercial electricity use, depending upon region, the toll of unneeded energy consumption in the U.S. alone exceeds 700 million barrels of oil per year, based upon estimates that almost half of commercial lighting may be wasted (including unneeded overnight lighting of office buildings, forsaking available natural light, underutilization of occupancy sensors, and under-using discretionary light controls). In response to these concerns, the design and architecture communities are making greater use of indirect sunlight in modern commercial buildings.
Adverse health effects from excessive lighting or incorrect spectra can manifest in the form of headaches, fatigue, stress, sexual effects, increased risk of certain carcinomas, high blood pressure and other cardiovascular disease. Some of these effects are under further study to understand the exact causes.
Numerical definition of over-illumination
Generally speaking over-illumination occurs indoors when light levels exceed 500 lux for incidental lighting, exceed 800 lux for general office use or exceed 1,600 lux for special purpose use such as microchip etching quality control. For comparison, the midday sun provides about 32,000 to 100,000 lux depending on latitude, time of year and cloud cover. The term over-illumination first came into reasonably broad use in the early 1990s, when the lighting, health and energy conservation fields realized its effects. Production of glare is a de facto indication of over-illumination, since that causes optical processing conflicts and confusion to the brain in translating optical inputs. The reason over-illumination is sometimes grouped with incorrect spectra is that the health effects are linked, and also because incorrect spectra (such as that provided by fluorescent lamps) provide too intense illumination in certain frequency bands compared to other bands. The most-desired spectrum is that of natural light, which the body is expecting and which is used to set the circadian rhythms of all higher forms of animal life.
Over-illumination is considered to be a subset of light pollution issues. In particular over-illumination can generally be considered as more outdoor illumination than the light user himself requires, whereas light pollution is also (and primarily) concerned with stray light or illumination of subjects other than those intended by the illuminator. Over-illumination is a topic normally addressed in the process of building design, whereas light pollution is normally addressed in the venue of zoning violations and as an annoyance to others not on the illuminator's property. Furthermore, over-illumination does not refer to the extreme conditions of snowblindness or arc eye, in which ultraviolet light can induce physical damage to the cornea.
Causes of over-illumination
Lighting unoccupied areas is responsible for significant energy wastage. A 2005 survey of commercial buildings indicates that only about five percent of structures utilize any form of occupancy sensor, a device that has been available for over 15 years. More remarkably office buildings are often illuminated overnight and on weekends. A survey of building managers indicates this practice was primarily for the convenience of the janitors, so that they would not have to bother turning lights on and off during night shifts when janitorial work was carried out. Timers are also available to switch light banks off at prescribed times, a practice particularly useful to prevent outdoor lights from staying on during daylight. One survey of 156 California building managers revealed that average daylight use of outdoor lighting was one to two hours, and the reason for such wastage was most commonly attributed to the failure of building maintenance personnel to reset timers for each season (i.e. quarterly reprogramming that takes approximately two minutes per timer).
Forsaking use of sunlight is often a design decision made by the architect or their subcontractor. Overlooking opportunities for skylights is a major defect of many building designs, but lack of coordination of interior light banks with indirect sunlight is an even more common error. At a minimum, the building design should offer sufficient independent light banks so that building occupants may select the most suitable combination of natural to augmented light. Very frequently entire floors of office buildings are designed with only one switch, so that perimeter areas near natural light are illuminated with the same level of man-made light as the dimmest interior zones. This lack of independent controls also would require an entire office floor of say 10,000 square feet to be fully illuminated if one office worker stays late for evening work. This can occur with even the most eminent of architects. Frank Lloyd Wright designed Marin County Civic Center in 1957 with only one or two switches serving very large floor footprint office pools. This cost Marin County several thousands of dollars per annum in unneeded electricity costs.
Omitting occupancy sensors is an error primarily for bathrooms, conference rooms and storage areas. This is an energy wastage issue and not a health issue. The payback time of most occupancy sensors is in the range of two to five years, and yet first cost economics prevent the installation of occupancy sensors in the majority of cases where they would save energy and lighting maintenance costs.
Failure to delamp or use available lighting controls is a common issue associated with over-illuminated buildings. Many instances of “designed in” over-illumination can be corrected by simple actions of building managers, following an illumination survey. In many instances over-illumination can be solved by removing a fraction of the lights or fixtures from a ceiling lighting system. In other cases a lighting retrofit can be conducted to replace older, less energy efficient fixtures with newer ones. Lighting retrofits can also be designed to reduce over-illumination; retrofits have typical payback periods of two to four years. In simpler cases many fluorescent ceiling illumination systems have multiple switch settings that allow tuning of the light intensity delivered, the most common version of this control being the "three-way switch". Much of the benefit of the excess illumination reduction comes from a better ratio of natural light to fluorescent light that can result from any of the above changes. Research has been conducted showing worker productivity gains in settings where each worker selects his own lighting level.
Effects of over-illumination
Headaches, fatigue, stress and performance effects
Health effects of over-illumination or improper spectral composition of light include increased headache incidence, worker fatigue, medically defined stress, decrease in sexual function and increase in anxiety. The health consequences are particularly significant of improperly matching the color spectrum of sunlight when illuminating the workplace. Clinical studies documented in the foregoing references have been conducted for each of these health effects, except for sexual dysfunction, in which case only a linkage has been suggested through the decreased endothelial function associated with hypertensive increase. All these effects are dealt with within the present section, except for sexual dysfunction, which is most closely associated with the hypertensive effects and addressed under major health effects.
Migraine headaches are known to be triggered by excessive light. In one survey over-illumination was listed as the number two trigger for migraines, with 47% of the respondents reporting bright light as the principal trigger of their migraine episode. Not only does bright light induce headache, but incorrect spectra (for example, too great an emphasis upon fluorescent (as opposed to sunlight) contribute to incidence of headache.
Fatigue is a common complaint from individuals exposed to over-illumination, especially with fluorescent media.. Some studies have shown that the flicker and over-illumination combined in some fluorescent systems yield particularly high fatigue incidence. Research on circadian rhythm in humans indicates that one reason for fatigue stems from the incorrect color spectrum of fluorescent light.
Stress and anxiety are frequent outcomes from working in a setting of intense (especially fluorescent) lighting. Research has shown that annoyance from bright light leads to medical stress. It is clear that brighter, less spectrally correct light induces clinically measurable stress, and it is suggested that for children this over-illumination may interfere with the learning process. For example, in dysgraphia, a defect of learning to write, children experiencing any form of stress are subject to greater incidence of this learning disability. Task performance can also be compromised for people conducting work under artificial (e.g. fluorescent as opposed to natural light). The annoyance with purely artificial light and preference by office workers for natural light has been demonstrated by a number of studies spanning eastern and western cultures. Fluorescent lighting has also been linked to aggravating other psychological disorders such as agoraphobia.
Circulatory and circadian rhythm effects
Hypertension effects of over-illumination can lead to aggravation of cardiovascular disease and erectile dysfunction, which impacts are outcomes of long term cumulative exposure and associated systematic increases in blood pressure. The mechanism of this effect seems to be stress by related up-regulation of adrenaline production akin to the fight-or-flight response. When adrenalin is released into the bloodstream it causes vasoconstriction, a known precursor to both hypertension and erectile dysfunction. Analogous female sexual side effects are thought to result in the female anatomy from reduced blood flows.
Circadian rhythm disruption can be caused by too much light, too little light, or incorrect spectral composition of light. This effect is driven by stimulus (or lack of stimulus) to the pineal gland, the body’s photometer, that thence signals the brain as to time of day. If the body is totally deprived of light for too long a time, the body's clock is thrown off. Bright light also inhibits production of melatonin, a substance shown to reduce cardiac arrythmias and to reduce oxidized lipids in the ischemic heart. Melatonin also reduces superoxide production and myeloperoxide (an enzyme in neutrophils which produces hypochlorous acid) during ischemia-reperfusion. .
In practice, adverse outcomes seem to arise most commonly among workers subject to intense fluorescent light, which is poorly matched to the spectrum of sunlight. According to one set of researchers, the body translates this condition as "total darkness" and resets the circadian clock incorrectly. Not only does this result in fatigue, but also immuno-suppressive behavior that has been shown to be linked to increased cancers. The research indicates that increasing the ratio of natural light to artificial solves much of the problem, provided the total illumination level is not driven excessively high. Many of these health impacts may be primarily due to the spectrum of the light rather than the overall level of illumination, but more research is required to establish this.
Energy and economic considerations
The total worldwide energy wastage from over-illumination is roughly 1.5 billion barrels of oil per annum. Most of the excess occurs in the U.S. and Europe. Japan, while highly industrialized, has a very different ethic in terms of avoidance of unneeded light; this equation has been changing in Tokyo itself in the past two decades. Excessive energy usage is often tolerated because the person who bears the cost is usually not the one making day to day decisions about lighting. Building managers and not building owners usually structure such things as janitorial use of lighting, setting or installation of timers, or the choice of lighting fixtures. Another poor management practice in the U.S. is a leasing structure where the tenant, who makes operational decisions on lighting use, pays none of the electricity costs, a form of lease common in about one half of the situations today.
There are also myths which continue to propagate, occluding better lighting decisions. One myth is that there is a greater cost of turning on fluorescent systems than keeping them running. In particular, according to the U.S. Department of Energy: "The amount of electricity consumed to supply the inrush current [for turning a fluorescent light on] is equal to a few seconds or less of normal light operation. Turning off fluorescent lights for more than five seconds will save more energy than will be consumed in turning them back on again." Another myth is that electrical costs of lighting are a constant and not a variable. However, hundreds of buildings in the U.S. have been audited and had their lighting use altered, with a demonstrated 30 to 50 percent reduction in lighting costs. For example one California study indicated that generally 40 to 80 percent of lighting energy costs could be eliminated, sometimes requiring hardware investment with an average payback time of less than two years. Obviously the highest savings can be generated for buildings in the planning stage or where major remodeling will occur. A final myth is that more light is better. Health data disprove such an assertion, and this statement only has applicability in rare situations today where the original lighting is very low or where unusual technological manufacturing processes (such as microchip etching) demand high illumination levels.
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