Two-sphere test of the polygon light curve algorithm. We can even use a very coarse discretisation of 42 nodes for each sphere, because we compute partial eclipses, partial occultations, or partial transits. Shades of gray show the monochromatic intensity I_λ (in W m⁻² sr⁻¹ m⁻¹), green lines show the non-eclipsed and non-occulted polygons used to compute the surface areas. The orange arrow shows the direction towards the Sun and blue towards the observer. The test bodies are metre-sized, 1 au from the Sun and 1 au from the observer. See also Fig. 2.