Lighting Research Center Lighting Research Center
    Volume 11 Issue 2
September 2010    
ballast - A device required by electric-discharge light sources such as fluorescent or HID lamps to regulate voltage and current supplied to the lamp during start and throughout operation. bi-level switching - Control of light source intensity at two discrete levels in addition to off. color rendering index (CRI) - A rating index commonly used to represent how well a light source renders the colors of objects that it illuminates. For a CRI value of 100, the maximum value, the colors of objects can be expected to be seen as they would appear under an incandescent or daylight spectrum of the same correlated color temperature (CCT). Sources with CRI values less than 50 are generally regarded as rendering colors poorly, that is, colors may appear unnatural. continuous dimming - Control of a light source's intensity to practically any value within a given operating range. high-intensity discharge (HID) - An electric lamp that produces light directly from an arc discharge under high pressure. Metal halide, high-pressure sodium, and mercury vapor are types of HID lamps. restrike time - The time required for a lamp to restrike, or start, and to return to 90% of its stabilized light output after the lamp is extinguished. Normally, HID lamps need to cool before they can be restarted. visual performance - The quantitative assessment of the performance of a visual task, taking into consideration speed and accuracy. high-pressure sodium (HPS) - A high-intensity discharge lamp type that uses sodium under high pressure as the primary light-producing element. HPS lamps produce light with a correlated color temperature (CCT) of approximately 2000 kelvins, although CCTs for lamps having higher CRI values range from 2200 to 2700 kelvins. Standard lamps have a CRI value of 22; others have CRI values from 60 to 80. HPS lamps are among the most efficacious light sources, with efficacies as high as 150 lumens per watt, although those with higher CRI values have efficacies as low as 25 lumens per watt. lamp life - The median life span of a very large number of lamps (also known as the average rated life). Half of the lamps in a sample are likely to fail before the rated lamp life, and half are likely to survive beyond the rated lamp life. For discharge light sources, such as fluorescent and HID lamps, lamp life depends on the number of starts and the duration of the operating cycle each time the lamp is started. luminaire - A complete lighting unit consisting of a lamp or lamps and the parts designed to distribute the light, to position and protect the lamp(s), and to connect the lamp(s) to the power supply. (Also referred to as fixture.) correlated color temperature (CCT) - A specification for white light sources used to describe the dominant color tone along the dimension from warm (yellows and reds) to cool (blue). Lamps with a CCT rating below 3200 K are usually considered warm sources, whereas those with a CCT above 4000 K usually considered cool in appearance. Temperatures in between are considered neutral in appearance. Technically, CCT extends the practice of using temperature, in kelvins (K), for specifying the spectrum of light sources other than blackbody radiators. Incandescent lamps and daylight closely approximate the spectra of black body radiators at different temperatures and can be designated by the corresponding temperature of a blackbody radiator. The spectra of fluorescent and LED sources, however, differ substantially from black body radiators yet they can have a color appearance similar to a blackbody radiator of a particular temperature as given by CCT. efficacy - The ratio of the light output of a lamp (lumens) to its active power (watts), expressed as lumens per watt. illuminance - The amount of light (luminous flux) incident on a surface area. Illuminance is measured in footcandles (lumens/square foot) or lux (lumens/square meter). One footcandle equals 10.76 lux, although for convenience 10 lux commonly is used as the equivalent. metal halide (MH) lamp - A high-intensity discharge lamp type that uses mercury and several halide additives as light-producing elements. Metal halide lamps have better color properties than other HID lamp types because the different additives produce more visible wavelengths, resulting in a more complete spectrum. Metal halide lamps are available with CCTs from 2300 to 5400 K and with CRI values from 60 to 93. Efficacies of metal halide lamps typically range from 75 to 125 LPW. phosphors - Materials used in a light source to produce or modify its spectral emission distribution. In fluorescent and high intensity discharge lamps, the phosphors fluoresce (emit visible light) when excited by ultraviolet radiation produced by mercury vapor inside the lamp when energized by an electric arc. In a light emitting diode, phosphors convert short-wavelength light or ultraviolet radiation produced by a semiconductor die into longer-wavelength light, usually with the goal of producing white illumination. glare - The sensation produced by luminances within the visual field that are sufficiently greater than the luminance to which the eyes are adapted, which causes annoyance, discomfort, or loss in visual performance and visibility. sky glow - Brightening of the sky caused by outdoor lighting and natural atmospheric and celestial factors. ambient temperature - The temperature of the surrounding air that comes into contact with the lamp and ballast. Ambient temperature affects the light output and active power of fluorescent lamp/ballast systems. Each fluorescent lamp-ballast system has an optimum ambient temperature at which it produces maximum light output. Higher or lower temperatures reduce light output. For purposes of lamp/ballast tests, ambient temperature is measured at a point no more than 1 meter (3.3 feet) from the lamp and at the same height as the lamp. lumen maintenance - The ability of a lamp to retain its light output over time. Greater lumen maintenance means a lamp will remain brighter longer. The opposite of lumen maintenance is lumen depreciation, which represents the reduction of lumen output over time. Lamp lumen depreciation factor (LLD) is commonly used as a multiplier to the initial lumen rating in illuminance calculations to compensate for the lumen depreciation. The LLD factor is a dimensionless value between 0 and 1. footcandle (fc) - A measure of illuminance in lumens per square foot. One footcandle equals 10.76 lux, although for convenience 10 lux commonly is used as the equivalent. light trespass - A undesirable condition in which exterior light is cast where it is not wanted. lux (lx) - A measure of illuminance in lumens per square meter. One lux equals 0.093 footcandle. illumination - The process of using light to see objects at a particular location. pulse-width modulation - Operating a light source by very rapidly (faster than can be detected visually) switching it on and off to achieve intermediate values of average light output; the frequency and the duty cycle (percentage of time the source is switched on) are important parameters in the modulation. spectral power distribution (SPD) - A representation of the radiant power emitted by a light source as a function of wavelength. fluorescent lamp - A low-pressure mercury electric-discharge lamp in which a phosphor coating on the inside of the glass tubing transforms most of the ultraviolet energy created inside the lamp into visible light. light-emitting diode (LED) - A solid-state electronic device formed by a junction of P- and N-type semiconductor material that emits light when electric current passes through it. LED commonly refers to either the semiconductor by itself, i.e. the chip, or the entire lamp package including the chip, electrical leads, optics and encasement. dynamic outdoor lighting - Outdoor lighting that varies light level or other characteristics automatically and precisely in response to factors such as vacancy or the type of use of an outdoor location. light pollution - An unwanted consequence of outdoor lighting that includes such effects as sky glow, light trespass, and glare. reflectance - A measure of the ability of an object to reflect or absorb light, expressed as a unitless value between 0 and 1. A perfectly dark object has a reflectance of 0, and a perfectly white object has a reflectance of 1.
Are there any legal liabilities associated with dynamic outdoor lighting?

Put simply, the answer is yes, but the specific legal issues will vary among jurisdictions and will depend upon the specific circumstances. NLPIP conducted informal interviews with several trial attorneys in the U.S. and researched legal cases in U.S. federal and state courts that involved outdoor lighting as a possible factor relating to safety or security. NLPIP does not provide legal advice. Consulting an attorney familiar with the statutes and laws of the local, state/provincial, and federal jurisdictions is an important and useful course of action for a municipality or property owner considering use of a dynamic outdoor lighting strategy. The information in this section is provided to help facilitate, but not to replace, that consultation.

To demonstrate a legal liability related to dynamic outdoor lighting, several factors would need to be established such as whether the municipality or property owner had a duty to provide lighting for safety or security, whether there was a breach of this duty by the municipality or property owner, whether the breach of duty was in fact a cause of an injury, and whether the injury resulted in damages (Pinsonneault et al. v. Merchants and Farmers Bank and Trust Company et al. 2002). These factors are illustrated in Figure 11. The latter two factors are based on the circumstances surrounding a particular incident; therefore only the first two factors are discussed further.

Figure 11. Factors associated with the legal liability of outdoor lighting (based on Pinsonneault et al. v. Merchants and Farmers Bank and Trust Company et al. 2002)

Different jurisdictions impose different levels of duty. There may also be different levels of duty placed upon governmental agencies than on private property owners within the same jurisdiction. One court in California stated that unless there is a special circumstance that makes lighting absolutely necessary for safety, municipalities in that state have no duty to illuminate their streets (Antenor v. City of Los Angeles 1985). In Illinois, a court decision stated that municipalities have no duty to provide lighting for pedestrian safety except in crosswalks (Hough v. Kalousek and Village of Oak Lawn 1996), and another Illinois court stated that it is up to the municipality to decide if a street should be illuminated (Baran v. City of Chicago Heights 1968). Some local jurisdictions actually require reduced outdoor light levels after business hours (Fairfax County 2003). On the other hand, a court in Michigan ruled that illuminating a parking lot was part of a property owner's duty in order to maintain a safe place for employees (Sleeman v. Chesapeake & Ohio Railroad Company v. Barnaby and Parker 1968). There can be broadly varying interpretations in different jurisdictions about how the duty to provide nighttime illumination, if it is imposed, should be carried out. Standards and recommendations from organizations such as the Illuminating Engineering Society (IES) have been cited in Michigan cases as a basis for defining the appropriate level of duty (Sleeman v. Chesapeake & Ohio Railroad Company v. Barnaby and Parker 1968; Lane and Lane v. Ekrem Bardah of Fenton, Inc. and McDonald's Restaurants of Michigan, Inc., 2003). In at least one case in Illinois, a jury was permitted to consider IES recommendations in its deliberations about whether the duty was properly met (Baran v. City of Chicago Heights, 1968). In one Michigan case where a question arose of whether the outdoor lighting at a restaurant was on during an accident, lighting measurements made by an expert revealed that the light levels still conformed to IES recommendations even when the lights were turned off, and the court subsequently stated that because of these sufficient ambient conditions, the property owner did not breach its duty to provide lighting for safety (Lane and Lane v. Ekrem Bardah of Fenton, Inc. and McDonald's Restaurants of Michigan, Inc., 2003).

In a different case in California, a court determined that municipalities were not required to conform to IES standards in the provision of street lighting (Stathoulis et al. v. City of Montebello 2008). Furthermore, a court in Washington state ruled that darkness or low light levels alone did not excuse occupants from exercising ordinary care when walking or driving in an outdoor area (Roppo v. Motor Cargo and Unterwegner 1998).

Reliance on expert opinions regarding lighting and visual performance were also used in cases in order to help identify whether there was a breach of duty regarding lighting (Roppo v. Motor Cargo and Unterwegner 1998; Lane and Lane v. Ekrem Bardah of Fenton, Inc. and McDonald's Restaurants of Michigan, Inc. 2003). In at least one case, a court in Illinois stated that although there was not automatically a duty of municipalities to illuminate streets, once the duty was assumed by a municipality, the municipality was required to ensure that lighting was "reasonably safe and done skillfully" (Baran v. City of Chicago Heights 1968).

These issues suggest that a municipality or property owner should research whether there is a legal duty to provide lighting and if so, how to demonstrate that the duty is being properly carried out. Local ordinances requiring lighting may call for specific light levels or may be written in more general language. Local requirements generally supersede industry standards and recommendations, such as those published by the IES. The attorneys interviewed by NLPIP noted that having a written plan for lighting to provide safety, using assessments by experts in lighting and visibility during the design phase, and providing documentation explaining any deviations from standards or recommendations could reduce a property owner’s legal liability.

Not all reasons for implementing dynamic outdoor lighting would be treated equally in a court case. The attorneys interviewed by NLPIP suggested that the desire to reduce operating costs and energy use would not necessarily excuse a property owner from a duty to provide lighting for safety. Environmental factors such as mitigation of light pollution (for example, light trespass onto a residential neighbor's property) could be perceived as a reasonable basis for reducing light levels through dynamic outdoor lighting, but it is unlikely that this factor would be considered as important as safety in a legal case.

Liability issues will continue to be a barrier to implementing dynamic outdoor lighting. Local ordinances that require light levels to be reduced after certain hours, such as those in Fairfax County (2003), Virginia, are not widespread, and depending upon the local jurisdiction, reduction of light levels could create exposure to legal liability. Municipalities and property owners can take specific actions to reduce exposure to liability, including the preparation of written plans for lighting and safety, visual assessments of reduced light levels (if used) and documentation of factors, such as reducing light trespass, that could justify lower light levels. Again, NLPIP recommends that municipalities and property owners who wish to consider dynamic outdoor lighting consult an attorney familiar with the local, state, and federal requirements for lighting during the lighting planning and design stages.


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