be set up to sound a chime as well as turn on the light. Most modern units have a photocell so that they only turn on when it is dark. To reduce light pollution, the International Dark-Sky Association recommends the use of downward-facing security lights that preserve and protect the night time environment. During the South African energy crisis increased rates of metal theft, house breaking and robberies were reported in areas effected by the loss of security lighting due to a loss of electricity in some urban areas. Limitations An important limitation to the usefulness of security lighting is the simple fact that it is only useful at night. This is particularly significant for home owners because, contrary to a widespread myth, most household burglaries occur during the day, when the occupants are away at work or shopping. As with any lighting, security lighting can reduce night vision, making it harder to see into areas that are unlit or are in shadow. Non-uniform illumination may also interfere with surveillance systems, as the wide dynamic range of security cameras may have difficulty adjusting to the changes in light intensity. See also Access control Environmental design Light pollution Physical Security Security Security engineering References Lighting Security Architectural lighting design