In my last post, Pedestrian Lighting: A Case Study, I outlined a recent JDB Illumination commission to provide pedestrian lighting for a neighborhood adjacent to a college campus. Exterior lighting is critical to create a safe environment whether for a college campus, business park, urban environment, parking lot, public park, or anywhere else. Lighting designers need to evaluate two important design objectives when designing pedestrian lighting, which we refer to as Illumination for Safety and Illumination for Security. These may seem similar, but in reality they are very different.
Illumination for Safety
Illumination for Safety refers to the proper amount of illumination required for a person to detect a hazard and take appropriate action to mitigate that hazard. It is intended for safe navigation of pedestrians while on foot, bike, or other normal means of non-motorized transportation. The primary area of evaluation is typically the “street adjacent” pedestrian way or bike way, otherwise known as a sidewalk or path. The illumination of these areas is intended to help pedestrians and bikers identify potential tripping hazards such as uneven pavement, tree roots, debris, and changes in elevation.
Illumination for Safety focuses on the horizontal plane, meaning the ground, as well as the color of the light. We measure the average amount of light on the horizontal plane at finished grade in foot candles. The purpose is to verify that there is enough light present to identify tripping hazards. Lamp color is measured by the kelvin temperature of the lamp. For instance, a kelvin temperature of 4000K provides a white light that increases the perceived appearance of higher illumination levels compared to lower kelvin temperatures, which create a yellow color cast. The yellow cast, while providing sufficient illumination, can appear dimly lit and affect the perceived brightness.
Illumination for Security
Illumination for Security is focused on protecting people, property, and public spaces from harm. It is defined as the proper amount of illumination required for a person to perceive and evaluate potential threats. The intent of design is to illuminate the vertical plane, particularly the face, body, and hands of other persons. This illumination allows the pedestrian to evaluate approaching persons by analyzing facial gestures, hand positions, body language, and potential weapons. The evaluation is typically done subconsciously, and the approaching person is classified as a threat or non-threat.
In addition to a focus on the vertical plane, Illumination for Security also seeks to reduce disability glare. Vertical illumination is the average amount of light, measured in foot candles, on a vertical surface located 6’-0” above finished grade and parallel to the path of travel. An example would be the face of an approaching pedestrian. The average is computed in both directions along the path of travel to verify that threats can be identified regardless of which direction you are walking. Glare is a visual sensation caused by excessive and uncontrolled brightness. It can be disabling (disability glare) or simply uncomfortable (discomfort glare).
An example of disability glare is when you are driving West directly into the setting sun. This often create a situation that is dangerous because the “sun in your eyes” limits your ability to see the road. Disability glare causes a reduction in visibility due to intense light sources in the field of view.
An example of discomfort glare is when the bright sun is overhead, causing you to put on sunglasses so you don’t need to squint. It is uncomfortable but does not dramatically impact your vision. Discomfort glare creates a sensation of annoyance, or even pain, induced by overly bright light sources.
Glare is subjective, and sensitivity to glare can vary widely among individuals. For pedestrian lighting, providing luminaries that shield the lamp source from direct view can reduce or eliminate both disability and discomfort glare.
Codes, Ordinances, and Standards
Although some cities and municipalities have code requirements for pedestrian lighting, many areas have none.
However, there are several professional standards that provide recommended methods for the design of pedestrian lighting. Most of these standards provide a methodology, but not specific illumination criteria. Where specific criteria are provided, they are presented as guidelines, and allow for practical installation, site-specific requirements, and ambient lighting criteria to modify the general guidelines. These professional standards have been published by the Illumination Society of North America (IESNA), with some criteria jointly created with other entities such as the International Dark-Sky Association (IDA) and the American National Standards Institute (ANSI). These guidelines include:
- Design Guideline: Recommended Lighting for Walkways & Class 1 Bikeways (IESNA DG-5-94)
- Guideline for Security Lighting for People, Property, and Public Spaces (IESNA DG-1-03)
- Recommended Practice: Roadway Lighting (IESNA RP-8-2014)
- Recommended Practice: Lighting for Exterior Environments (IESNA RP-33-2014)
- The Lighting Handbook: Reference and Application (10th Edition)
- Model Lighting Ordinance (Joint IDA/IES MLO)
As JDB Illumination worked on the college pedestrian lighting project, we conducted a review of various model ordinances, then compared them to the recommendations presented in the professional standards. The ordinance we reviewed included:
- District of Columbia Department of Transportation (DDOT)
- New York City Department of Transportation
- San Francisco, California
- Baltimore City Department of Transportation, Maryland
- City of San Diego, California
- City of Redmond, Washington
The table below compiles these various ordinance illumination levels and professional standard recommendations. Once this was reviewed, a recommendation was made for the illumination levels for this particular project.
EAVG (FC): Average Horizontal Illumination measured at grade in Foot Candles
EMIN(FC): Minimum Horizontal Illumination measured at grade in Foot Candles
EV(FC): Minimum Vertical Illumination measured at 6’ above graded in Foot Candles
EAVG/EMIN: Ratio of Average to Minimum Horizontal Illumination
Lighting design professionals must consider numerous variables when Illuminating for Safety and Illuminating for Security. The JDB recommendation for the college campus might not be the correct recommendation for another application, but it does provide a useful baseline for beginning the conversation.
Connect with Craig
- LinkedIn: https://www.linkedin.com/in/craig-malesic-9a4b4923/
- Twitter: https://twitter.com/CMalesic