All incandescent and halogen light bulbs should be replaced immediately with compact fluorescent lamps or LED versions, they found, assuming an average use of 3 hours per day. But if you are already using compact fluorescent lamps then the next step depends on several factors.

"If your main goal is to reduce overall carbon dioxide emissions, then you should switch to LEDs now," Lixi Liu told environmentalresearchweb. "However, if you are aiming to minimize costs or energy consumption overall then waiting until LEDs are available that use even less energy and are more affordable may be the most desirable option."

The group, which also includes Gregory Keoleian and Kasu Saitou, based its analysis on 60 W-equivalent light bulbs, a common choice in US households.

Their replacement model considers not just the type of lamp currently in use – incandescent, halogen, compact fluorescent or LED – but also examines how lighting technologies could evolve over coming years as well as future changes in the composition of the electricity grid.

The researchers note that lamps used most often should be replaced first to maximize energy savings, and suggest that households shouldn't necessarily wait until the bulb has blown before installing a new lamp.

"Replacing a light bulb before it burns out seems wasteful, but this study shows that you can save more energy by replacing the bulb earlier," said Liu. "Replacing LED-based lamps before they burn out should be considered because cheaper models that use less energy are likely to become available long before the current ones burn out."

Based on this finding, the scientists suggest that manufacturers should focus on making LED bulbs more energy efficient before making them longer lasting. In addition, the team advocates recycling programmes for household lamps as well as pursuing strategies to dematerialize and modularize designs for ease of disassembly and component replacement.

Liu and colleagues published their results in Environmental Research Letters (ERL).