might need to be increased in complex environments, but conversely can be reduced in very open environments. Multiple lamps of moderate power instead of a few powerful lamps will reduce glare, provide more even illumination with reduced pools of shadow, and provide some redundancy if one lamp's bulb blows out or develops a bad ballast. Prevent malicious tampering or interference. This means that besides the lamp itself, the entire circuit from the source (electric company or generator), through the wires, to the lamp and back should be protected. Luminaires should be accessible so that the maintainer can replace blown bulbs as quickly as possible and clean the luminaires periodically. However they should be protected or somehow made inaccessible to tampering. Ensure the electric meter box is locked or inaccessible, or else power the lights from a different line. Control and power lines, where outside or vulnerable, should be either buried well underground (in conduits preferably) or at a height of at least 8 metres (about 24 feet). Ideally multiple circuits should be used to prevent an accidental or malicious short or cut causing all illumination to fail. Use Security lighting can be used in residential, commercial, industrial, institutional, and military settings. Some examples of security lighting include floodlights and low pressure sodium vapour lights. Most lights intended to be left on all night are high-intensity discharge lamps as these have good energy efficiency, thus reducing the cost of running a lamp for such long periods. A disadvantage of low pressure sodium lamps is that the colour is pure yellow, so the illuminated scene is seen without any colour differentiation. Consequently, high pressure sodium vapour lamps (which are still yellowish, but closer to golden white) are also used, at the cost of greater running expenses and increased light pollution. High pressure sodium lamps also take slightly longer to restrike after a power interruption. LED-based security lighting is becoming increasingly popular, due to its low electrical consumption (compared to non-LED lighting technologies), long lifespan, and options for different color spectrum ranges. Other lights may be activated by sensors such as passive infrared sensors (PIRs), turning on only when a person (or other mammal) approaches. PIR sensor activation can increase both the deterrent effect (since the intruder knows that he has been detected) and the detection effect (since a person will be attracted to the sudden increase in light). Some PIR units can