When you purchase a bulb, check its packaging for any restrictions on use. For example, some bulbs should not be used in enclosed fixtures and some may specify that the base be up or down. Many are for specific fixtures, such as recessed cans, dimmer switches or outdoor fixtures. Bulbs used incorrectly can cause fire and/or electric shock. This pertains to incandescent bulbs as well, such as using a 100-watt bulb in a fixture that calls for 40 watts.

Source: UF/IFAS Energy Efficient Homes: Fluorescent Lighting, Hyun-Jeong Lee, Kathleen C. Ruppert, and Wendell A. Porter, FCS3270, 2008

Additional Resources
UF IFAS Energy Efficient Homes: Fluorescent Lighting - http://edis.ifas.ufl.edu/FY1031

Consortium for Energy Efficiency. (2007).  Residential lighting. Retrieved April, 18, 2008, from http://www.cee1.org/resrc/facts/rs-lt-fx.pdf

ENERGY STAR®. (2008, April) Frequently asked questions: Information on compact fluorescent light bulbs (CFLs) and Mercury, April 2008. Retrieved May 5, 2008, from http://www.energystar.gov/ia/partners/promotions/change_light/downloads/Fact_Sheet_Mercury.pdf