Which aspect of luminaires is critical to ensure their safe operation?

B is critical for ensuring the safe operation of luminaires because the mounting and stability of the light fixture are essential for preventing accidents and ensuring effective illumination. Proper mounting ensures that the luminaire can withstand environmental factors such as vibrations, impacts, and any other forces that may occur during normal operation. If a luminaire is not securely mounted, it could fall or become misaligned, leading to potential safety hazards such as electrical shock or fire risk as well as physical injury to individuals nearby. The NEC emphasizes the importance of securing fixtures to maintain not only safety but also functionality, making this aspect of luminaires paramount in their design and installation.