Give some stream of consciousness and then the answer. H-alpha (H) is a specific deep-red visible spectral line in the Balmer series with a wavelength of 656.28 nm in air; it occurs when a hydrogen electron falls from its third to second lowest energy level. H-alpha light is important to astronomers as it is emitted by many emission nebulae and can be used to observe features in the Sun's atmosphere, including solar prominences and the chromosphere.

Based on this passage, when is h alpha line in the emission spectrum of hydrogen atom obtained?
The relevant sentence in the passage is: H-alpha (H) is a specific deep-red visible spectral line in the Balmer series with a wavelength of 656.28 nm in air; it occurs when a hydrogen electron falls from its third to second lowest energy level.
Therefore, the answer is when a hydrogen electron falls from its third to second lowest energy level.