Which of the following is NOT one of the types of nebulae observable in visible light?

Globular nebulae are actually not a recognized type of nebula observable in visible light because the term "globular" refers primarily to globular clusters, which are tightly bound collections of stars. Globular clusters do not exhibit the nebular properties such as the emission or reflection of light that characterize other types of nebulae.

Bright nebulae, planetary nebulae, and dark nebulae are all specific categories of nebulae observable in visible light. Bright nebulae emit light themselves, often due to the ionization of gas by nearby hot stars. Planetary nebulae are formed when a star expels its outer layers at the end of its life cycle, creating a shell of glowing gas. Dark nebulae, on the other hand, are clouds of gas and dust that block light from objects behind them, making them visible as dark patches against the background of stars. Thus, the correct answer highlights the distinction that globular nebulae do not exist as a type of nebula in observational astronomy.