The invention relates to a projection system for a display, in particular a heads-up display, comprising a liquid crystal screen (12) and a back-lighting device (14) for said screen (12). The projection system is characterized in that said back-lighting device (14) comprises at least one light source (16) emitting light towards the screen (12), at least one lens (38a, 38b) suitable for collimating the light from the light source (16) towards the liquid-crystal screen (12), and reflective means (26) arranged on the surface of the lens (38a, 38b) located on the side of the light source (16), arranged such as to allow light to pass through same towards the screen (12) and to reflect towards the screen (12) almost all of the light propagating towards the lens (38a, 38b).