Energy efficiency means delivering the same service -- light, cooling, motion -- while consuming less energy, which makes it one of the cheapest ways to reduce both cost and environmental impact, since saved energy requires no new generation at all. Common sources of waste include incandescent lighting, which converts most of its energy into heat rather than light, and poorly insulated or ventilated buildings that rely heavily on artificial cooling. Practical steps include switching to LED bulbs, which use significantly less energy than incandescent bulbs for the same brightness and last far longer, choosing appliances with efficiency ratings, and designing spaces to make use of natural light and airflow.