Plants use certain frequencies of light to power photosynthesis. Most plants absorb red and blue light and reflect most other colours. By using red and blue LEDs instead of broad-spectrum incandescent lights, you can save a lot of energy. Although LED grow lights will cost more initially, in the long run the electricity savings will more than make up for the cost.
Buy four red and two blue 2.95 volt 350 milliamp LEDs such as the Luxeon star Lambertian LEDs, as well as an LED driver and a connector (see Resources section).
Scavenge a box or crate that is tall and wide enough to fit your plants inside when it's standing on end. A wine crate would work well, as would an old refrigerator or large cardboard box.
Cover the inside of the box with aluminium foil. You can use glue or tape to attach it.
Attach the LEDs to the inside of the box with tape so they are facing the plants. Solder the LEDs in series using insulated copper wire (see Resources below). Plug the connector into the driver and solder the ends onto the LEDs appropriate LEDs. Plug the driver into the wall to test it.
Lean or tape a mirror to the opening if you are using a box with an open top such as a wine crate. This will keep more of the light inside the box.
Some growers prefer to use large numbers of dimmer LEDs instead of a few ultra-bright ones. Using just a few makes things easier to wire and set up, however.
These LEDs draw a lot of current, and can get quite warm. If your plants are temperature sensitive, double check how hot the box gets before closing the open side.