The invention relates to a bioreactor comprising a tank containing a culture medium in which a cell culture composed of algae cells is dispersed. The cell culture of algae has a concentration greater than 0.1 g/L in the culture medium, and each algal cell has a minimum absorption in a specific range of wavelengths of light. The bioreactor comprises a light source that is capable of emitting incident light in the direction of the tank, 60% of the photons of the incident light having a wavelength which is included in said specific range of wavelengths of light. The invention also relates to the use of the bioreactor for the production of biomass.