Before using a CFL in a totally enclosed fixture, you should consult the product packaging. CFLs that are not designed for totally enclosed fixtures will typically carry a disclaimer that indicates that they are not intended for this type of application. Because totally enclosed fixtures do not allow air to circulate around the lamp, it causes heat to build up, which can lead to performance issues.
Though CFLs do not produce nearly as much heat as incandescents, they are more sensitive to heat, which can effect their performance. Some of the components in a CFL can not withstand high heat, unless specifically engineered to do so. The excess heat that is created in a totally enclosed fixture can cause the light output to be diminished, the bulb to appear to "dim" more quickly than CFLs used in applications that allow airflow, and a shorter bulb lifetime. The most effective way at this time to ensure that the particular product you are interested in purchasing is designed to withstand high-heat applications, is to check the packaging or contact the manufacturer directly.