Transitional lighting is particularly important for security considerations. This provides a gradual light level change from a brightly lighted area to a dark area so as to eliminate the vision impairment resulting from passage into a dark area out of a brightly lit area. The four general types of outside security lighting are (1) continuous lighting, which provides glare projection or controlled lighting; (2) standby lighting, which is designed for reserve or standby use as well as to supplement continuous systems; (3) portable lighting, which can be used in particular locations for short periods; and (4) emergency lighting, which can be used when other systems are inoperative for whatever reason. General types of lighting sources are incandescent, mercury vapor, fluorescent, metal halide, and sodium vapor. Four types of lighting equipment generally associated with security lighting are flood lights, street lights, fresnel units, and search lights. Lighting can be controlled automatically through a timer or the photoelectric cell. Even with the emphasis on energy conservation, research has shown security lighting to be such a crime deterrent that it is cost-effective. The appendix discusses protective lighting requirements, characteristics, the security director's responsibility, planning, principles of protective lighting, types of lighting, lighting applications, wiring systems, maintenance, and power sources.