Yale University scientists say switching from incandescent light bulbs to compact fluorescent bulbs can increase mercury emissions, depending on how energy is generated and waste handled.

Certain countries may be trading energy conservation for more toxic air emissions with their use of compact fluorescent lighting, say U.S. researchers.

In a study of 130 countries and 50 states, Yale University scientists concluded that in some places mercury emissions have been increased by switching from incandescent light bulbs to compact fluorescents.

The study appears online in Wednesday's journal of Environmental Science and Technology.

The results of the Yale study depend on a complex set of factors, including whether a country relies on coal-powered electricity, the type of coal used, and whether they have recycling programs for compact fluorescents (CFLs).

Coal combustion is the single largest source of atmospheric mercury pollution, and the reduced energy demand from CFLs leads to reduced emissions from coal plants. But CFLs contain small amounts of mercury, which can be emitted into the atmosphere when bulbs break during transportation, when they are vaporized during incineration and when they are sent to landfills, which release the mercury into the air.

It's important to reduce mercury emissions, because chronic exposure can cause damage to the brain, spinal cord, kidneys and liver. Developing fetuses and children are at particular risk.

The researchers found countries that derive much of their energy from coal, such as Estonia and China, can significantly reduce mercury emissions by using CFLs. Other countries in a similar situation include Romania, Bulgaria and Greece.

But places like California and Norway on the other hand, which get most of their power from non-coal sources, may end up putting more mercury into the atmosphere by using CFLs.

Also on the list of regions that may end up emitting more mercury are parts of South America, Africa, the Middle East and parts of Europe, along with Alaska, California, Oregon, Idaho and several New England states.

While the researchers included Canada in their calculations, they didn't break down their findings by territories or provinces — some of which rely on coal. They found Canada, in general, would not reduce mercury emissions significantly by switching to CFLs. They did not comment on their potential effect on energy conservation.

Ottawa has announced it will phase out incandescent bulbs by 2012. The ban is expected to help reduce greenhouse gas emissions by more than six million tonnes a year and save homeowners about $60 annually in electricity costs.