Cloudy model spectral energy distribution of I Zw 18. The flux distribution of the stellar population incident on the inner edge of the H ii region is shown in white, the stellar flux transmitted to the H i region in gray. The wavelength of the ionization edge of relevant species is given along the top of the figure. The H ii region absorbs virtually all the H i Lyman continuum and converts it to H i Lyα, nebular continuum, and line emission (all shown in red).