Flux difference between a cloudy Venus-twin exoplanet (opaque H₂SO₄ clouds) and an icy world with a thin CO₂-dominated atmosphere (see Appendix E for a comparison of the absolute fluxes). In brown, we plot the flux residual of the icy world with respect to the Venus twin as a function of wavelength. The gray shaded region indicates the 1 σ LIFESIM noise level at S/N = 10. The thin, hatched, and black area represents the expected wavelength-dependent noise for the LUVOIR A mission concept (The LUVOIR Team 2019); the thick, solid black line represents the expected noise for the HabEx + Starshade mission concept (Gaudi et al. 2020).