Usually the lights only need to be on sometimes. But in our home, we find that they are left on in the hall and the laundry room, and we finally realized why: those are places where your hands are usually full, and it's hard to operate the switch. Ergo, the light stays on.
In our time in Denmark, we've also seen occupancy sensors used extensively in bathrooms, which just seems more hygienic to us: one less thing to clean. Shopping tips after the jump...
Look for the following features:
• Field of view: measured in degrees, as viewed from above. The ideal is 180°, which would mean a full view of the room, but most are slightly less than this.
• Manual override: sometimes you want the light on anyway; but in most situations, choose a switch without a manual override, as they tend to get switched on and forgotten.
• Time-delay interval: use two switches, for example, to turn the light off 15 seconds after someone leaves a bathroom, and the exaust fan off after 15 minutes.
If you've used a particular brand, please let us know about your experience.