A device for trapping all available light and organizing it into any given beam by means of an optical device which, by forcing a fluid to rotate in a suitably-shaped space (1) (revolution or non-revolution of a logarithmic spiral arc), enables a temperature gradient to be created, thus causing a refractive index gradient to be maintained in a fluid chosen for its ability to transmit or absorb part of the light flux according to the wavelength thereof. All the light may be concentrated and channeled in the desired direction while the heat energy not needed for visual projection is removed. A spotlight or still picture projector having excellent optical efficiency (no heat-absorbing glass) and unlimited power may thereby be obtained.