down the rabbit hole

Lighting at the End of the Rabbit Hole: How to Determine Appropriate Lighting Levels as Part of a Total Security Program

Dana Frentz, CHPA, PSPSecurity Assessment, Security Program Development

Beginning Down the Rabbit Hole

lightingWe all know the use of lighting alone does not stop crime, but the effects of good lighting coupled with additional security measures have been shown to reduce the occurrence of crime. Lighting can elicit an emotional response, providing a level of confidence and the feeling of security. It can also provide a decrease in the perception of crime. Think of how light deterred the boogeyman when your children were young.

Security managers use lighting as a preventive and corrective measure against break-ins, trespassing, and criminal activity on physical property. The goal of security lighting is to illuminate a person, an object or a place to allow observation and identification. By utilizing the glare effect on the human eye, lighting creates a physical deterrent; this can also create a psychological deterrent by leading potential attackers to believe that they will be discovered and observed.

Recently, while conducting a light study, I found myself asking “If someone gave me this information what might I say”? Me being me, I would ask WHY? How do security professionals make decisions as to what level of light is needed in certain areas? How is it determined? So I set out to find the answers, or at least a better way of explaining to my clients how the Illumination Engineering Society (IES) determined the needed foot candle/lux for specific locations (1). Little did I know I was jumping deep into a rabbit hole.

Quality Characteristics of Lighting – Visibility, Color Rendering, Glare, Uniformity, and Shadows

No single security device or method will work in every situation. Similarly, no single set of values for lighting will work in every circumstance. By providing multiple layers of security, practitioners can “harden the target” and further provide a safe and secure environment. Therefore, these multiple layers should include lighting.


The reflective capabilities of the surrounding environment, (i.e. the pavement and the façade of a building) directly affect visibility. Lighting levels will vary depending on the reflective properties of the building and pavement. A dark façade will absorb more of the light’s reflective properties. In contrast, a light colored façade will enhance the light’s reflection. The quality of lighting includes factors such as color rendering, uniformity, glare and shadowing.

Color Rendering

Color rendering relates to the way objects appear under a given light source. Experts call this measure the “color rendering index”, or CRI. A low CRI indicates that objects may appear unnatural under the light source. A light with a high CRI rating will allow an object’s colors to appear more natural. Without getting too far into the weeds, think of how lighting can be warm or cool. Warm light gives off a yellow to orange color while cool light provides a bluer to whiter color. The warmer the light the lower the CRI rating, and the higher the CRI the cooler the light. High-pressure sodium lighting seen in street lights can be as low as 22 CRI, and compact fluorescent lighting (warm white) can range from 80-85 CRI.


Glare refers to the difficulty of seeing in the presence of bright light, such as direct light from fixtures or reflected light from the sun. It is generally divided into two types: discomfort glare and disability glare. Discomfort glare may induce discomfort when looking at an object but may not interfere with visibility Disability glare is the effect light has on the eye, reducing visibility, but not necessarily causing discomfort.


Uniformity is the even distribution of light on a surface. It is determined by comparing the minimum, average and maximum light in a ratio of average to minimum or maximum to minimum. When lighting is uniform, even low levels of light can provide the feeling of a secure environment, as the eyes do not need to adjust to variations of bright and dark.


Shadows can diminish the feeling of a secure environment, by reducing the effectiveness of lighting. The blocking of a light source causes darkness or diminished light and creates dim to dark areas of visibility.

How well a space or area is lit should directly support the activities and characteristics in the area. The environment can have a direct effect on the physical and psychological state of the persons in the area. Consultants recommend lighting based on task, context and the human observer by using the science of lighting, coupled with a common sense approach. Consensus is what comes by joining the results found in lighting research and the need for practical, reasonable and quantitative recommendations for levels and ratios of lighting.

It is easy to become dazed when delving into the technical wonders of lighting; measuring lumens and lux, evaluating uniformities, mounting heights and watts. Ultimately security professionals should gauge lighting in terms of the visibility it offers and the perception it provides.

Variables in Deciding How Much Light to Use

Lighting is a science, but deciding how much light or what kind of light can be very subjective. The goal of security lighting is to help protect property and people from criminal activity as well as provide a feeling of safety and security. Values given as the illuminance targets found in the IES Lighting Handbook are based on consensus and are considered appropriate based on the functional activities listed. By utilizing knowledge of activity levels and base or ambient lighting, as well as the age of the observer, security professionals can determine the acceptable level of illumination.

IES divides Activity Levels into Indoor and Outdoor High, Medium and Low levels. Outdoor activity levels address night time hours.

High levels of activity have pedestrian or vehicle traffic high in volume or extreme swings of very high volume over a short period of time. These include outdoor facilities that hold large volumes of people, such as sporting arenas, university campuses or large shopping areas. Medium levels have moderate levels of pedestrian traffic coupled with some amount of consistent activity over extended periods of time. Examples include civic and cultural districts, college campuses and recreation centers. Low activity level has low to very low volumes of people, and is relative to the density of the population. These facilities include typical rural or suburban locations.

Lighting Zones

IES describes ambient light in the Lighting Zones. There are five Lighting Zones ranging from No Ambient light, LZ-0 to High ambient light, LZ-4.


LZ-0 is a default zone for wilderness areas, parks and protected wildlife areas. There is no ambient lighting. Lighting would adversely affect these areas. Lighting would impact the biological cycles of flora and fauna and would detract from human enjoyment and appreciation of the natural environment. Think of turtle nesting.


LZ-1 has a low ambient light level and is a default zone for rural and low density residential areas. Districts zoned as agricultural, rural residential and business parks are typically LZ-1. These are areas where lighting might adversely affect flora and fauna or disturb the character of the area. The vision of human residents and users will adapt to the low light levels.


LZ-2 has moderate ambient light, and users’ vision adapts to moderate light levels. This is generally a default zone for light commercial business districts, high density or mixed use residential districts, churches, schools and neighborhood recreation facilities or light industrial areas, which have modest nighttime activity or lighting requirements.


LZ-3 has moderately high ambient lighting, where the vision of human residents and users adapts to moderately high light levels. This is typically the default zone for large cities, business districts, business zone districts, commercial mixed use, and heavy industrial and/or manufacturing zone districts.


LZ-4 is not a default zone. This includes areas with high intensity business or industrial zones and the human eye has adapted to intensely high levels of light. Think of a correctional institution.

These described Zones and Activity Levels help practitioners determine the appropriate level of lighting for the location or task. This is based on the recommended illuminance targets and the age of the observer. These targets are vertical and horizontal light levels that should be maintained for each specific application.

Determining Light Levels

Measuring light levels is the easy part; however, rendering the final determination of a light level can be confusing. Use a light meter to accurately measure light levels a light level meter. Nearly all outdoor applications have target levels for both horizontal and vertical illumination.

Horizontal Illumination

Horizontal illumination defines the intensity or availability of light across an area. Surveyors make horizontal measurements by pointing the light meter sensor toward the horizontal surface. For example, a parking deck ceiling, canopy, porte-cochère, or the sky.

Vertical Illumination

Vertical illumination defines intensity or availability of light as it rises above the ground or surface. As a result, surveyors make vertical measurements by pointing the light meter sensor toward the vertical surface measured. For example, a wall, door or building façade.

Vertical illuminance allows for the identification of facial features and body language. IES recommends that people need facial identification at 30 feet. This allows about 5-6 seconds for two people walking toward each other to meet, thus allowing a decision of avoiding, fleeing, ignoring or defending against the other person if necessary.

Consideration must be taken if there is a specific direction that must be viewed. For instance, a security checkpoint’s view should be toward the officer or person checking the credentials. A widely accepted method for determining vertical measurements when there is not a prescribed direction determined is to take four measurements. By measuring north, east, south, and west and dividing it by four, the surveyor can obtain an average. If the average is above 0.6 foot candles and the lowest of the four readings is no less than one-fourth of that average, there should be enough vertical illumination to see and identify a face from 30 feet (2).

In addition to the concerns of being able to identify a face at a distance, pay attention to background silhouetting. If the background behind the face is more than four times the luminance on the face, then there will be a silhouette. Therefore, the surveyor should consider and determine the background direction and take measurements keeping the 4:1 ratio in mind.

Lighting and Security

Without a clear understating of the risks associated with a facility, a security program will not be effective. Effective lighting plays a critical role in the many components assuring a more safe and secure environment. Conduct complete lighting assessments at least annually, or when there are events that require updated information such as an accident, additional equipment installation, or new construction. Conduct monthly evaluations to assure all fixtures and lamps are functioning appropriately. Monthly evaluations should also ensure that repairs occur in a timely manner.

IES has made significant changes and advancements made in lighting since the last edition of the IES Lighting Handbook published more than ten years ago. There is an increase in the understanding of the connection between health and light, and awareness of how light affects our lives and the environment. Like preceding editions, the 10th edition has been developed by blending science, technology and design into three distinct sections; Framework, Design, and Application.

In the Framework section there is an extensive explanation for understanding illumination targets, while the Application section provides a broad range of lighting criteria for many common purposes as well as some specialized locations such as correctional facilities and hospitals. The Application section contains much of the information needed for conducting a security light study. The 10th edition no longer provides complete descriptions of all aspects of a particular application. Instead, it relies on separate publications issued by the IES enabling more timely revisions and practice-based recommendations.

Conducting the Light Study

It is optimal for two people to conduct a light study. One can take the measurements and the other can document the findings. An assessment template can be beneficial in determining the locations for each reading. Site drawings should reflect the locations of fixtures with a legend of the types of fixtures. Site drawings should also show building entries and paths/sidewalks for pedestrian traffic. Also note critical points and areas of concern and record thorough measurements.

Pay attention to the quality, quantity and distribution of lighting during the survey. Are lamps emitting a suitable level of light? Does the lighting affect any other security measures in place such and security video cameras? Document what you see. Is the area awash in yellows and orange or are colors more true due to the type of lamps used? How will that affect perception? Is there adequate distribution of light? Are the lamps angled appropriately?

Light at the End of the Rabbit Hole

As first stated, lighting is not the lone security measure to assure an effective security posture. Security professionals use other security and crime prevention concepts to enhance a safe and secure environment. Understanding how those concepts work in conjunction with lighting is an important step. For example, Crime Prevention Through Environmental Design (CPTED) is a concept that emphasizes that lighting, vegetation management, traffic flow, pedestrian flow, and other physical attributes can be manipulated to lessen the opportunity of a crime-related event occurring in a particular location.

Above all, complete security assessment can provide an organization with many areas on which to focus their attention to enhance their security program. By having a clearer understanding of the processes used to determine recommended targets for lighting, I can now provide a more robust and complete report for clients that has recommendations based on best practice as well as science.

1. The foot-candle is the common non-metric unit for measuring light. One foot-candle is the amount of light produced by one candle at the distance of one foot.
2. IESNA G-1-03

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