Lyman-α radiation dominates the ultraviolet spectra of G, K, and M stars and is a major photodissociation source for H2O, CO2, and CH4 in the upper atmospheres of exoplanets. We obtain intrinsic Lyman-α line fluxes for late-type stars by correcting for interstellar absorption or by scaling from other spectroscopic observables. When stars flare, all emission lines brighten by large factors as shown by HST spectra. We describe photochemical models of the atmosphere of the mini-Neptune GJ 436b (Miguel et al. 2015) that show the effects of flaring Lyman-α fluxes on atmospheric chemical abundances.
