This one's pretty straight forward - go around your house and replace any incandescent bulbs with LEDs or Compact Fluorescent Light (CFL) bulbs.
Inefficient incandescent bulbs are much harder to come by these days, so it's likely you may have already done this with most of the bulbs in your house. Take a quick look anyway to see if you've missed any.
Extra Info & Tips
There's a bit of an upfront cost to this one since you'll have to buy the bulbs, but over time you should actually make a saving.
When you get rid of any old bulbs or eventually any of the new ones you've replaced, try and dispose of them responsibly. Below is a rough guide on how to do so - remember this may vary depending on what your local recycling can deal with.
Standard incandescent light bulbs and halogen lamps can be thrown away with household waste. They cannot be recycled as regular glass because the fine wires in glass processing are very difficult to separate out, making the cost to recycle these items prohibitive.
Compact fluorescent lamps and fluorescent tubesshould not end up in household waste. They contain small amounts of mercury. Although this is completely safe for users of the lamps, they must be collected separately for disposal. This ensures that valuable parts of the lamps, such as glass and metal, are not lost. Check your local recycling to see where and how you can dispose of these safely.
LEDs do not contain harmful substances like CFLs. You should look for the disposal rules that apply to the equipment in which they are incorporated. Individual LEDs can be disposed of in household waste.
More About Light Bulbs
We could go on forever about the differences between these light bulbs. However eartheasy.com have managed to put together content on energy efficient light bulbs which will take you through everything you'll ever want to know.
There's also lots of information about different lighting solutions on the internet and a quick search should bring back ample results to check out.
Just starting or have you completed this challenge?