The earlier units used infrared technology would keep the lights on only when a warm body moved in front of them. If the sensor did not “see” any motion for a few minutes, the lights would go out.
The funniest poke at this that I remember was in a Dilbert cartoon. They hired temporary workers to wave their arms to keep the lights on in the engineering department where Dilbert works.
The newer units have dual technology that includes an ultrasonic listening device. They keep the lights on when it hears unusual sounds. These units teach themselves what the normal empty room noises are.
After they learn to ignore the sounds from the heating system, as example, they allow the lights to go off. That way the lights stay on until the unit cannot see any warm body motion and cannot hear anyone in the area. Warm body motion is still what turns the lights on but they do not go off until the noise is quiet for a time.
If you are in a restroom and the person in the next stall is whistling they may just be trying to keep the lights on.
These devices use electrical power to do their job of saving energy.
The low-end single technology units need to have a tiny flow of current to operate. That means that some power must flow through the light bulbs for them to work. This is not a problem for old fashion incandescent light bulbs. But, there is a problem with fluorescent lights. The small current flow, that powers the sensor, is enough to make fluorescent lamps flicker or never go completely out. That is why the inexpensive two-wire sensors do not work with compact fluorescent lamps (CFL’s).
This problem is solved by spending a little more money for a better sensor that has two parts, a sensor and a relay. The motion sensor operates all the time on its own power circuit and the sensor tells the relay when to switch the power on or off to the lights. They have three wires that need to be connected in the lighting circuit.
The more you spend the more you get.
The dual technology units have an infrared sensor plus an ultrasonic sensor and a separate black box. The black box is called other names like “power pack with load switch.” It takes in the supply power, passes it to the sensor, receives the go or no go signal from the sensor and turns a relay switch on or off to send power to the lights. There are about eight wires connected to the magic black box.
You need someone who can connect all eight wires to the right places. They should check the power draw to make sure you bought properly rated hardware.
In an office or commercial building the cost of buying the parts and pieces and connecting it all together will likely be paid off in a couple of years. That means the savings on the electrical bill will pay for the cost of installation in about two years. From then on, the savings is like money in the bank.
When working on a project like this I let my fingers do the shopping at Graybar.com. After I find what I need in their online catalog, I call them up for pricing. Then I can calculate the return on investment information for my client.
In general, occupancy sensors are a good investment for business. The problem for home use is that there are very few lamps wired to each motion sensor. Sometimes there is just one lamp controlled by a motion detector.
To make the worthwhile you need to use the least expensive sensor unit that will do the job and be patient. Expect a 3-year or longer payback, even though you use free do-it-yourself labor.
Motion sensors provide savings two ways.
First, you reduce the use of electricity by automatically shutting the lights off when they are not needed. That reduces your electric bills.
Second, the lamps will last longer because they are not on as much. You will not have to replace the light bulbs as often saving money on the maintenance budget.
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