Workplace Illumination – Part 17: Nuisance Light

            Light that does not contribute to its intended purpose, i.e. visual performance in a defined area, is wasted.  When it detracts from the experience of surrounding areas, light is obtrusive.  Wasted light is often obtrusive, but need not be to contribute to nuisance.  Systems that produce little wasted light also contribute to nuisance.  The existence of nuisance light is bothersome irrespective of its impact on visual performance, though it can be significant.
            Several aspects of nuisance light, also known as “light pollution,” are considered in this installment of the “Workplace Illumination” series.  Many parallels are evident between light pollution and “noise pollution.”  Review “Occupational Soundscapes – Part 15:  Community Noise” [15May2024] for a presentation of the latter; read on for a discussion of the former.

            Sources vary in their use of terminology related to this topic.  Light pollution has been the term of choice for many to refer, collectively, to unwanted effects of artificial light.  However, this term may evoke the notion of a biological toxin, prompting a visceral response.  If not the goal of the term’s coining, this response is useful to activists.  Though biological effects can indeed result from errant light, the term nuisance light is favored in this presentation to recognize its broader impacts and maintain objectivity.

Types of Nuisance Light
            An example of a mast-mounted luminaire installation is depicted in Exhibit 1, with contributions to nuisance light labeled.  Nuisance light is typically described as consisting of three components:  sky glow, light trespass, and glare.

            Sky glow is the luminance of the night sky in excess of that produced by natural sources, such as moonlight or starlight.  Light emitted slightly above the horizontal (90 - 95°) (see “direct upward light” in Exhibit 1) is the greatest contributor to sky glow; light emitted in the 5° bands above and below this are also significant.  Contribution to sky glow of light emitted in various ranges of angle from the vertical are tabulated in Exhibit 2.  Light emitted in the range of 85 - 100° creates the bright “dome” visible at long distances; above 100°, the light is visible only at much shorter distances or from above.
            Sky glow is often associated with large metropolitan areas, where details of the night sky are almost totally obscured.  Small towns and individual sites, however, also generate substantial amounts of nuisance light.  Oil refineries, other processing plants, and dockyards (shipping ports), for example, are notorious for their sky glow.  In addition to direct emission, light can also be reflected upward from the many structures and surfaces present at these sites (akin to groundlight in the daylighting context), intensifying sky glow.
            Environmental factors also influence the intensity of sky glow.  Specifically, water vapor (humidity, clouds) and particulate matter (dust, pollen, pollutants) in the air diffuse light.  In fact, air itself also does so; light is subject to greater diffusion at low altitude due to the higher air density than that at high altitude.  Unlike sound, light is not directly affected by wind; however, a wind-blown dust cloud, for example, could distort the shape of a sky glow dome, “carrying” light further from the site than it might otherwise be visible (i.e. in still air).

            Light trespass occurs when light is incident where it is unwanted.  Not only does this light provide no benefit to the task area (i.e. it is wasted light), but it is a detriment to the irradiated space.  Any of the types of light shown in Exhibit 1 can be obtrusive, or trespass, depending on the characteristics of the task area, lighting system, and surrounding areas.
            Errant light is not necessarily obtrusive; unintended illuminance of an unutilized space could be inconsequential.  A negative impact on the illuminated area or an occupant’s visual field is implicit in the term light trespass.  Reduced visual performance, ecological disruptions, degraded aesthetics, or other issues may result.
            When light trespass occurs on a window of a nearby structure, light intrusion occurs.  A common concern is light intrusion of residential properties that effects circadian timing (see Part 4) and quality of life.  Light intrusion through bedroom windows is particularly egregious, as it can reduce the quantity and quality of sleep, negatively impacting well-being and potentially leading to long-term health effects.
The Institution of Lighting Professionals (ILP) has deemed light trespass a disfavored term, preferring spill light be used.  Spill light is that outside the intended target of illuminance; both direct and reflected light may contribute.  This is an unfortunate change in position by the ILP for a few reasons.
            First, overuse of similar terms can confuse would-be practitioners.  Spill light is the consequence of a light spill, the emission and/or reflection of light into unintended spaces.  The definition of light spill is conspicuously similar to that of light trespass, with one important distinction:   a light spill is the source of trespass, but its occurrence does not guarantee a trespass, as explained previously.
            Second, the stated logic for the change is flawed:  “…trespass is to physically encroach on land and light can’t do that…”  Both the premise and the conclusion are erroneous.  Trespass can refer to any type of transgression, not only physical acts.  This misguided premise is mooted, however, because light (i.e. radiation) is a physical phenomenon.  Therefore, the conclusion that “light can’t do that” is patently false, even if the premise is accepted.
            Finally, a change in terminology should provide a clearly articulable benefit to discussions of the subject matter; clarity, accuracy, and differentiation are common, laudable objectives.  The title of this installment provides a relevant example.  As explained in the introduction, supplanting light pollution with nuisance light provides an intuitive entry point to discussion of the topic and tags the phenomenon with appropriate stigma.
            The value of the terminology shift adopted by ILP is dubious at best.  It does not provide clarity, it reduces it.  Even those who are not lighting professionals intuitively understand light trespass is “light where it doesn’t belong;” for this reason, it remains an accurate, useful term.

            The effects of glare on visual performance and comfort are discussed in other installments of this series.  Particularly relevant to this discussion is the “Lighting Conditions” section of Part 9, briefly revisited here to link glare to nuisance light.
            Glare is quintessential nuisance; at its least severe, the consequence may be only a minor distraction.  Discomfort and disability glare are significantly more bothersome, decreasing visual performance and increasing risk for both personal injury and task failure.  The potential for glare corresponding to the angle of emission from a luminaire is tabulated in Exhibit 2.  Shades, other forms of shielding, and specialized eyewear may be used to minimize the impact of glare.  However, doing so is also a burden, often borne by those subject to, but not responsible for, adverse lighting conditions.  Its detrimental effects and that it is often avoidable undoubtedly qualifies glare to be labeled nuisance light.

Principles of Responsible Lighting
            Like any precious resource, light should be delivered only in the quantity required, in the limited area required, and during the period of time required.  The desire for energy conservation has provided the simplest and most-salient support of responsible lighting, reminding us to turn off lights any time they are not needed.  This is the “when” of lighting, as in “only when needed.”  Visual task performance, safety, security, and emergency situations dictate when lighting is required.  Other concepts in responsible lighting may be less intuitive, but it is easy to understand that light that is not emitted cannot contribute to nuisance.
            The “where” of lighting seems equally straightforward until one considers the challenges of achieving illuminance “only where needed.”  One objective is to eliminate spill light and, thus, light trespass.  Effectively directing light to a task area also minimizes glare and contributions to sky glow.
            The type of luminaire used and its mounting configuration are critical to effective light direction.  The beam angle should be 70° or less, as shown in Exhibit 3, to minimize glare.  Mounting luminaires at greater height facilitates achieving low beam angles.  As shown in Exhibit 4, this also reduces spill light and shortens shadows.

            Luminaires should be shielded or constructed with reflectors that achieve a beam angle below 70° and cutoff within the task area; an example of each approach is depicted in Exhibit 5.  Many styles of luminaire are now available with shielded designs to minimize nuisance light.  Externally, they are often indistinguishable from their unshielded counterparts, allowing lighting performance to be upgraded without affecting aesthetics.
            Shielding can also be achieved externally when necessary.  The prevention of nuisance light by both internal and external shielding of vertical illuminance is depicted in Exhibit 6.  Building facades and billboards are typically lighted this way.  Vertical and horizontal illuminances are managed by the same methods.
            Providing an appropriate quantity of light is achieved through source selection and control strategies.  A light source must be capable of providing the maximum illuminance required, while controls reduce output when lower illuminance suffices.  Daylighting, dimming, occupancy sensors, and other controls can be combined to minimize nuisance light.
            The spectral makeup of light also influences its contribution to nuisance.  Artificial light affects circadian rhythms in humans, photosynthesis in plants, and navigation, feeding, and other behaviors in animals.  Surface reflectances are also spectrally dependent.  For example, asphalt and concrete surfaces reflect more long-wavelength light than short-wavelength.  Thus, a parking lot illuminated by sodium lamps may contribute more to nuisance light than if it were illuminated by LEDs, for example.  Despite this, warmer colors (i.e lower CCT) are generally recommended for their lesser ecological impact.  Filtering can be used to modify a lamp’s output, though it may impact its efficacy.
            The International Dark-Sky Association (IDA) and the Illuminating Engineering Society (IES) provide a useful summary of considerations to minimize nuisance light in their “Five Principles for Responsible Outdoor Lighting,” shown in Exhibit 7.  A design process can be defined that adheres to these principles.  Descriptions of this process may differ among organizations, but the fundamental basis and objectives served remain the same.

Regulation Contemplation
            Lighting restrictions, like those on noise, can be imposed by various levels of government and administrative bodies.  A number of states have passed legislation to curb energy use, reduce sky glow, and protect natural habitats.  Many of the existing statutes are quite similar, suggesting that advocacy for the use of regulatory templates has been successful.  One such template is the IES/IDA Model Lighting Ordinance, which provides guidelines for limiting obtrusive light.
            Common features of state legislation include the limitation of scope to the prohibition of use of state funds to install or replace components of a lighting system that do not meet standards for nuisance light.  Unless local ordinances are also adopted, privately-owned and -operated installations remain unregulated.  A generic “exceptions may apply” provision leaves attainment of objectives subject to lobbying, interpretations, and other influences.
            Recommendations for the control of light, based on characteristics of an area, have been developed by various organizations.  The IDA, ILP, and CIE have developed systems of zones in which the recommendations for light management are defined.  A summary of some aspects of these overlapping systems is provided in Exhibit 8.

            Zone identification systems can be referenced directly, facilitating adoption of a model ordinance or crafting of unique legislation.  The recommendations for upward light ratio (ULR) and vertical illuminance (Ev), cited in Exhibit 8, come from ILP.  The recommended luminance limits for electronic message centers (EMCs) were developed by IDA.  Sky Quality Meter (SQM) values are also cited in zone descriptions; SQM measures the brightness of the night sky.  Values range from 16.0 to 22.0, where lower numbers indicate higher luminances.  Visit the IDA website for more information on this measurement and other assessment methods.
            Established curfews reduce energy consumption and wasted light by requiring that artificial light be dimmed or extinguished during periods of disuse.  Curfew periods vary by jurisdiction and area characteristics, but usually fall within the hours of 11 PM to 7 AM.  Most lighting is unnecessary after the curfew periods ends.  However, control of EMC luminance remains important in early-morning hours.  Likewise, waning daylight prior to the curfew period warrants a gradual reduction in luminance.

Final Thoughts
            The infographics in Exhibit 9 put the scale of the nuisance light problem in perspective.  According to IDA, an astonishing 99% of outdoor light is wasted.  To visualize this, consider the light pollution map in Exhibit 10; a color-coded SQM scale is overlaid on a map of the continental United States.  Major cities across the country appear as “hot spots,” where the sky glow is many, many times brighter than the natural sky.  Light that can be seen from space provides no benefit there, nor here on earth, yet consumes resources and ruins natural views.

            For additional guidance or assistance with Safety, Health, and Environmental (SHE) issues, or other Operations challenges, feel free to leave a comment, contact JayWink Solutions, or schedule an appointment.

            For a directory of “Workplace Illumination” volumes on “The Third Degree,” see Part 1:  An Introduction to Lighting (21Aug2024).

References
[Link] Lighting for Health and Safety.  N.A. Smith.  Butterworth-Heinemann; 2000.
[Link] The IESNA Lighting Handbook, 9ed.  Mark S. Rea (ed).  Illuminating Engineering Society of North America; 2000.
[Link] “Model Lighting Ordinance (MLO).”  Illuminating Engineering Society and International Dark-Sky Association; June 15, 2011.
[Link] Human Factors in Lighting, 3ed.  Peter R. Boyce.  CRC Press; 2014.
[Link] Handbook of Advanced Lighting Technology.  Robert Karlicek, Ching-Cherng Sun, Georges Zissis, Ruiqing Ma (eds).  Springer International Publishing; 2017.
[Link] “Guidance for Electronic Message Centers (EMCs).”  The International Dark-Sky Association; May 10, 2019.
[Link] “The Reduction of Obtrusive Light.”  Guidance Note GN01/21.  Institution of Lighting Professionals; 2021.
[Link] “States Shut Out Light Pollution.”  Jennifer Schultz.  National Conference of State Legislatures; March 25, 2022.

Jody W. Phelps, MSc, PMP®, MBA
Principal Consultant
JayWink Solutions, LLC
[email protected]