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. These effects may depend on the spectra of the light as well as the overall illuminance.

Lighting accounts for roughly 9% of U.S. residential electricity use. Areas where energy and financial savings could be realized include 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.

Numerical definition

Generally speaking, over-illumination occurs indoors when light levels exceed 500 lux for incidental lighting, 800 lux for general office use, or 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 processing optical inputs. Over-illumination is sometimes grouped with unnatural spectra because negative health effects may result from the excess illumination, and also because certain artificial lights (such as fluorescent lamps) provide intense illumination in certain frequency bands, unlike daylight, whose spectral power distribution is fairly even over the visible spectrum. The most desirable spectrum is that of natural light, which the body is attuned to and uses to set the circadian rhythms.

Related phenomena

Over-illumination can contribute to light pollution, where stray light illuminates the outdoors or others' property, where it is unwanted. Over-illumination is a topic normally addressed in the process of building design, whereas light pollution is normally addressed by zoning regulations.

Furthermore, over-illumination generally does not refer to the extreme conditions of snowblindness or arc eye, in which ultraviolet light can induce physical damage to the cornea.


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 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 or her own lighting level.

Health effects

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.

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, children experiencing any form of stress are more likely to suffer from dysgraphia, a problem in learning to write. 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 upregulation 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 is primarily caused by the wrong timing of light in reference to the circadian phase. It can also be affected by too much light, too little light, or incorrect spectral composition of light. This effect is driven by stimulus (or lack of stimulus) to photosensitive ganglion cells in the retina. The "time of day", the circadian phase, is signalled to the pineal gland, the body’s photometer, by the suprachiasmatic nucleus. Bright light in the evening or in the early morning shifts the phase of the production of melatonin (see Phase response curve, PRC). Wrong melatonin rhythm can worsen cardiac arrhythmias and increase 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. 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. 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. 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.

Architectural design can identify technological aspects of window design where window angles can be calculated to minimize interior glare and reduce interior over-illumination, while at the same time reducing solar heat loading and subsequent demand for air conditioning as energy conservation techniques. For the Dakin Building in Brisbane, California the angled window projections effectively provide permanent sunscreens, obviating any need for interior blinds or shades.

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