One of the first energy saving devices I installed in my town-home when we moved in last year was an occupancy sensor for my kitchen lights. The model was from Leviton and can be seen here.
The concept is extremely simple. When my Wife or I enters the kitchen the light comes on. When we leave the kitchen the lights go off (after a minute or two). The passive infrared sensor operates by measuring infrared light (heat) emitted by us as we enter into the kitchen. Basically, we alter the temperature when we enter the room and move around in it, and the device picks that up. If we come into the kitchen and sit down at the table to read the paper and don't move for a few minutes, the light may go off because the temperature has stabilized. This requires the simple task of waving an arm.
The occupancy sensor has two settings:
- How long the light stays on after no motion is detected: 15s-15m
- How much incoming light it detects before it comes on
The first setting is obvious. The "incoming light" setting is pretty cool. It means that during the day, if the sensor senses enough light it will not turn on even if it senses motion. Once it gets a little darker, it will turn on when motion is sensed. Both of these settings are adjusted with little dials on the side of the device and may require some tweaking so your wife doesn't get too upset when the light doesn't come on!
But if the automatic setting is too much for some, there is a switch on the bottom to operate the light like a normal light switch.
I would recommend one of these occupancy sensors wherever you might have a lot of lights controlled by one switch (meaning it costs you much more whenever the light switch is left on) or you have a light your family members are constantly leaving on.
The sensor cost around $15 at Home Depot. The circuit I have it on controls 10 lights. Before I had changed some of the lights to CFLs they were all 60 watt bulbs. Therefore, if someone forgot to turn off the light and it was left on for an hour, I consumed 600 Wh (60 watts x 10 lights x 1 hr.) of energy. Which is a little over a nickel worth of energy (Let's assume I pay 10 cents/kWh).
But if someone forgets to turn off the switch and the light circuit is left on an extra 5 hrs. a week, those lights will waste (5hrs. x 52 weeks x 60 watt x 10 lights) 156,000 Wh or 156 kWh. Remembering I pay 10 cents/kWh, and those lights that are left on cost me $15.60! I'd say a 1 year payback is pretty good!