The sensors normally used in this type of lighting are described as ‘passive’, since unlike so called ‘active’ sensors, they don’t emit any form of light, microwave or sound energy to detect movement. Instead they rely on picking up the temperature of a human body, and are tuned in such a way so as not to turn the light on when something like a cat or dog comes within range of the sensor.
They are also designed to only activate when the object emitting heat – i.e. a person – is moving reasonably quickly, this is so something like a warm stationary car won’t trigger the light, and in fact the light will switch off again if the person stands still for a while.
Motion sensor lights are quite easy to install and come in a variety of forms to suit your particular application. They can be wall or post mounted and come with single or multiple lights which can use LED or halogen bulbs; with LED lights producing much less light than halogen ones. Obviously the main consideration when installing the lights is the coverage of the sensor.
The sensor itself is adjustable on just about all models, so you can angle it to achieve the best effect, but you will need to pay attention to the maximum distance at which the sensor will reliably detect motion. A good quality model should work out to about 50 – 75 feet and cover an arc of around 200 degrees; it’s a good idea to choose a model which will allow you to adjust the detection range or sensitivity.
You may well find that for good coverage of your motion sensor outdoor lighting you will need to install several units, but with good quality models available for under $40, this isn’t a very expensive proposition.