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Lighting
The possibility that lighting might have an impact on the incidence of crime was a topic of interest in the United States in the sixties. Municipalities across America improved their street lighting to combat crime and some encouraging results were reported, but on review there was no significant statistical evidence that improved street lighting influenced the level of crime. There was, however, an indication that the improved street lighting decreased the fear of crime.
It is mostly at night that the highest fear of crime occurs. Sometimes common sense or intuition enables good decision making; other times the physical senses alert one to danger. Although all of the senses provide information about the environment, it is through vision that the majority of information is acquired and processed by the brain. Vision, therefore, has a tremendous impact on the decision making process.
Lighting facilitates visual perception of a space and area around the observer, and the observers' ability to see. For security purposes, the important lighting criteria are illuminance, uniformity, glare and shadows.
Illuminance - Illuminance is the density of light that falls on a surface. Measurements are made using an illuminance meter, often referred to as a light meter. The primary unit of measurement for illuminance is lux (metric) or footcandle (US, English). The two primary planes for measuring illuminance are horizontal and vertical. As a general rule, values not specifically labeled as vertical, are assumed to be horizontal lux (footcandles). It should be noted that for security lighting, vertical illuminance is often more important than horizontal because of the need to identify people.
Uniformity - Uniformity refers to the evenness of the distribution of light on the surface(s). In determining uniformity, minimum, average, and maximum illuminances are compared using ratios; either average-to-minimum or maximum-to-minimum. Uniformity in security lighting aids security perception, while reducing the necessity for eye adjustment when scanning or using the area.
Glare - Glare is the sensation produced by luminances (within the visual field) that are sufficiently greater than the luminance to which the eyes are adapted. Glare causes annoyance, discomfort, or loss in visual performance or visibility, and usually reduces the benefits of security lighting. There are two types of glare, disability glare and discomfort glare. Disability glare is the effect of stray light in the eye whereby visibility and visual performance are reduced. It can often be attributed to poorly shielded or non-cutoff luminaries. Discomfort glare produces discomfort but may not interfere with visual performance or visibility. Overhead glare is manifested by reflections off eye-glasses, eyelashes, cheekbones and other reflective areas around the eye. Direct glare results from high luminances or insufficiently shielded light sources in the field of view. Reflected glare is caused by a high luminance image on a specular or glossy surface, causing detail to be partially or totally obscured. Perimeter glare, however, when oriented to the outside of the site, may be desirable and useful in some secure sites to make the inside area less definable to would-be trespassers.
Shadows - Shadows reduce the effectiveness and impair security lighting. When shadows are sharply defined at or near an area, they may be annoying and discourage a feeling of safety. In addition, shadows make it difficult for users of a space or property and equipment to maintain quality surveillance. Shadows reduce uniformity of lighting.
Exterior Lighting
Exterior lights are important, especially near doors and in the rear of the house, where intruders do most of their work. All sides of your home should be protected with security lighting that is located high out of reach, and is vandal resistant. Lighting in carports and garages is critical. For garages, an automatic garage opener is the best choice. Almost every garage door opener made today has a light that comes on when the opener is activated, lighting the garage interior. In carports, it is best to either leave a light on, have a light on a timer, or have a light connected to a motion sensor or hot electric cell. A style of light that is used on the exterior is a motion detector type of fixture. The advantage to this type of light, especially in the back yard, is that the light warns the resident that someone is in their yard. While there is a concern that dogs, cats, or birds will trigger the sensor and cause the lights to come on, if the resident sets the sensitivity of the sensor correctly this will not be a problem. In the front yard, any type of lighting will be effective, as long the lighting pattern covers the entire front and sides of the house. Sensor lighting will be effective, but is more prone to false alarms caused by things like people walking down the sidewalk or children playing. Lighting should not produce glare or spill over (light trespass) onto your neighbors house.
Interior Lighting
When residents go out for an evening, they usually leave on their "burglar beacon." A burglar beacon is a small light that is left on so they don't walk into a dark house when they come home. These are lights like the one above the kitchen sink or stove, the hallway light, or a light in the corner of the living room. Unfortunately, for the criminal, these lights are a signal that no one is home. If you go out for an evening, leave several lights on. The radio or TV left on also gives an impression that someone is home. When you go on vacation put at least two lights, in different parts of the house, and a radio or TV on timers, all to go off at different times. Regardless of whether you are on vacation, or just gone for the evening, if looking at your house from the outside it should give the appearance that someone is home.
Parts of this information on lighting are taken from the Illuminating Engineering Society of North America publication, IESNA G-1-03, "Guideline for Security Lighting for People, Property, and Public Spaces."