Ordinary incandescent light bulbs are still widely used, as they are sturdy and cheap to produce. Energy-saving bulbs (e.g. fluorescent or LED) are a better alternative. They consume five times less energy than incandescent bulbs, and work for significantly longer. A LED bulb consumes half as much energy as a fluorescent bulb. A LED bulb is also safer both to use and to dispose of, as it does not contain mercury.
To save even more energy, you can install lamps with movement sensors.
By using energy-efficient light bulbs you can cut your electricity bill and reduce your use of non-renewable fossil fuels. And if you take your fluorescent bulb to be recycled, you can also avoid polluting the environment with mercury.