Final answer:
A hydrogen bulb emits light in certain colors because its electrons emit photons of specific wavelengths when they transition from excited to lower energy levels, creating its characteristic atomic emission spectrum.
Step-by-step explanation:
When a hydrogen bulb is able to give off light in certain colors, it's due to a process involving emission and absorption of light. Inside the bulb, when the hydrogen gas is heated up, the electrons within hydrogen atoms are excited to higher energy levels. As these excited electrons return to their lower energy levels, they emit light in specific wavelengths which correspond to distinct colors. For hydrogen, these colors are often seen as violet, blue, green, and red emission lines, with the most intense at 656 nm.
The unique set of colors, or the atomic emission spectrum of hydrogen, is due to the quantized energy levels within the atom. Whenever an electron transitions between these levels, it either absorbs or emits a photon with energy equal to the difference between the levels involved. For example, if white light passes through hydrogen gas, only photons with energies matching the transitions between energy levels of hydrogen will be absorbed, leaving dark lines known as an absorption spectrum. Conversely, when the electrons fall back to lower energy levels, they release photons with these specific energies, visible as bright lines in an emission spectrum.