Semi-conducting single-wall carbon nanotubes (S-SWCNT) have a direct band-gap and have always been thought as promising nano-objets for opto-electronic applications. However it turned out that their intrinsic properties and especially their ability to emit light are deeply altered by their interaction with the environment, which explains why the luminescence of SWCNTs was first reported only 10 years after the discovery of CNTs. Since then the emission of light from SWCNTs has been achieved in many configurations like individual suspended nanotubes with electrical injection, ensembles of nanotubes embedded in a matrix or micelle suspensions of nanotubes. From a fundamental physics viewpoint, optical properties of nanotubes are very exciting since they arise from a strongly confined one-dimensional object. This leads to enhanced Coulomb interactions resulting in strongly bound excitons which drive the optical properties of CNTs even at room temperature. The lift of the degeneracy of excitonic levels due to the crystallographic symmetries of CNTs results in dark states that play an important role in various optical properties such as luminescence quantum yield, phonon-assisted absorption or nonlinear properties. Finally I will present some recent results about new advanced materials based on functionnalized nanotubes. These open the way to new applications in the field of light-harvesting systems combining the versatility of the properties of dye molecules to the exceptional ones of carbon nanotubes.