Optical depth vs. atmospheric temperature in units of the effective temperature. A numerical solution obtained from Fortney et al. (2008) (thick black line) is compared to the semi-grey analytical solutions of Guillot (2010) for values of the greenhouse factor ranging from 0.01 to 100 (black to red lines). Low values of γ_v are redder. We used , T_irr = 1250K corresponding to the dayside average profile of a planet at 0.05  au from a sun-like star, and accounting for the albedo obtained in the numerical model. The internal temperature is T_int = 125  K and gravity 25ms^-2. The effective temperature of the studied slice of atmosphere¹ is defined by . For the numerical solution, the relation between pressure and optical depth was calculated using Rosseland mean opacities; TiO and VO opacities were not included.