A daylighting device collects and emits daylight as a natural alternative to electric lighting. Daylighting devices can be used even in rooms that have no windows or are normally in shadows.
Daylighting devices use lenses and mirrors to transmit sunlight. In this way, light can be "caught" at one location on a building's roof and run through tubes or optical fibers to a destination in another part of the building. Light can even bend around corners. But daylighting devices can't be a building's sole lighting source because there's no light for them to collect after sundown, and on a cloudy day their performance will not be optimal. Therefore, daylighting devices work better as supplemental light sources.
Not only are daylighting devices beneficial psychologically -- a lack of exposure to sunlight can cause seasonal affective disorder (SAD) -- they're also a good way to conserve energy. The more natural lighting you use, the less electricity you'll need, and the fewer light bulbs you'll have to replace as well. So not only is the use of daylighting devices "green," but it's also better for your pocket.
Of course, you'll have to pay for the initial installation (unless you want to spend a day installing it yourself) as well as for purchasing the device. A 10-inch (25.4 centimeter) SolaTube daylighting device costs about $650 (including installation), and prices go up from there. If you want extra features, such as a dimmer switch, you'll have to start adding to that price tag. An added benefit to the SolaTube device is that it provides sunlight exposure without the UV radiation, meaning that you won't get sunburn and your furniture won't fade. This will save you money in the long run too.