Simplified diagram illustrating the impact of the wavelength on the redshift distribution. Left panel: detection limit in bolometric infrared luminosity (L_IR) as a function of redshift for a S₂₅₀> 20 mJy (purple) and S₁₄₀₀> 1 mJy (gold). These limit are computed using the Magdis et al. (2012) main-sequence SED library. We neglected the scatter and the starburst populations to simplify this diagram. Right panel: number density of objects per redshift interval (computed from the luminosity function and the geometry of the Universe) as a function of the L_IR cut (x and y axis are inverted) at z = 1 (dashed line) and z = 4 (dot-dash line). These curves are computed using our model. The colored arrows represent the ratio between the number density of z = 1 and z = 4 sources. The black arrow highlights the increase in the luminosity and the decrease in the density of the knee of the LF between z = 1 and z = 4.