Properties of Security Lighting

Security lighting has several properties.

• Direction. Light from any source has a specific direction, but it can be reflected and refracted so that it becomes multidirectional (ambient) light. The directionality of security lighting can be arranged to accomplish two different purposes:
  
  
  • Silhouette an intruder. An intruder who is between the light source and the observation point is backlit or silhouetted.
    
    
  • Identify an intruder. The light must strike the intruder face-on and be reflected back to the observation point.
    
    
• Glare. Glare is discomfort produced by one or more sources of visible light. When appropriate, glare can be used deliberately against a potential intruder. Glare must be carefully controlled and managed so that it does not impede the effectiveness of CCTV or prevent employees from seeing an attacker.
  
  
• Illumination level. A light meter can be used to measure illumination level in footcandles or lux (in the metric system). Incident light meters measure the level of the light striking a target. Reflected light meters measure the level of light reflected by a target. Illumination levels measured by both types of meters are important to lighting security designers.
  
  
• Quality. Each type of artificial light source has its own spectral signature. Incandescent lights cover the entire visible spectrum while gas discharge lights (mercury vapor, metal halides, low- and high-pressure sodium) lights and fluorescent lights may cover only part of the spectrum. Lights that cover part of the spectrum can distort colors. For example, a piece of red material will look brown under low-pressure sodium light. This distortion must be considered if color CCTV cameras will be used. It must also be considered when security officers are taking witness statements that involve color descriptions.

To retain their effectiveness, lighting systems must be maintained. A poorly maintained lighting system can be exploited by a would-be attacker. A well-maintained lighting system—one in which damaged or burned out lamps are quickly replaced—sends a message about the facility’s attitude toward security to would-be attackers or persons gathering intelligence. A well-designed and well-maintained security and safety lighting system has a positive psychological effect on employees and visitors. It has the opposite effect on intruders.