How do bright nebulae produce or reflect visible light?

Bright nebulae produce or reflect visible light through two primary mechanisms depending on their physical properties and their proximity to stars:

Emission Nebulae

These nebulae emit their own light. They are typically associated with very hot stars (often exceeding 20,000 K) that radiate intense ultraviolet light. This radiation ionizes the surrounding hydrogen gas, stripping electrons from the nuclei. As these electrons and nuclei recombine and the atoms drop to lower energy levels, they emit visible light in characteristic emission lines. These regions, often called H II regions, effectively convert invisible ultraviolet energy into visible radiation.1234

Reflection Nebulae

These nebulae do not produce their own light; instead, they consist of interstellar dust that scatters and reflects the light of nearby, cooler stars. Because these stars are not hot enough to ionize the surrounding hydrogen, the nebula remains dark unless illuminated by the star's light. The dust grains act as excellent reflectors, scattering light across a broad range of wavelengths from the ultraviolet through the visible spectrum.3