For rendering a 3D scene comprising a surface and illuminated by an area light source (A), a glossy part of a radiance is represented by drawing samples between the light source and the surface according to a random sampling process exploiting a density function (L3). Two density distributions are determined: a first one associated with reflectance properties at a shading point of the surface and with a view direction (I), and a second one associated with geometrical properties of the light source. The density function for the shading point is obtained from a product of the first and second density distributions, which are represented respectively by a first and a second cosine lobes (L1, L2). Preferably, that density function is itself represented by a third cosine lobe (L3). Application to a GPU.