It seems hard to justify spending $4.00 for a compact fluorescent lightbulb when an ordinary incandescent lightbulb costs 50 ¢. To see if this makes sense, compare a 60 W incandescent bulb lasting 1000 hours to a 15 W compact fluorescent bulb having a lifetime of 10,000 hours. Both bulbs produce the same amount of visible light and are interchangeable. If electricity costs $0.10/kWh, what is the cost - purchase plus energy - to obtain 10,000 hours of light from each type of bulb? This is called the life-cycle cost.