What type of lights are permitted to be installed in ducts or plenums used for environmental air?

In ducts or plenums that are used for environmental air, it is crucial to use light fixtures that minimize fire hazards and meet specific safety standards. The correct choice, which refers to enclosed gasket type fixtures, is designed for such applications because they prevent the release of particles and contaminants into the air stream.

These fixtures have specific construction features, including sealed surfaces, which keep electrical components isolated from the airflow and reduce the chances of a fire starting. Their design ensures that they don't contribute to any airborne contaminants, thereby maintaining the cleanliness of the environmental air.

This choice aligns with the National Electrical Code (NEC) requirements and local electrical codes that emphasize safety in environments where air is circulated for heating, ventilation, and air conditioning (HVAC) purposes. The other options do not provide the necessary safety features to be considered suitable for installation in these areas, as they may pose potential risks such as overheating or contributing to air pollution.