Lighting system with light guiding body having trivalent cerium luminescent material

A lighting system comprising:

• a plurality of light sources configured to provide light source light at a wavelength selected from the range of 360 nm-490 nm;
• an elongated luminescent body having a length (L), and a height or diameter (H), the elongated luminescent body having light guiding properties, and the elongated luminescent body comprising:
• at least three side faces over at least part of the length (L), including a radiation input face, and a radiation exit window (112) bridging at least part of the height or diameter (H);
• a garnet type A3B5O12 luminescent material including trivalent cerium, with a height dependent concentration selected from a concentration range defined by a minimum concentration ymin=0.036*x−1 and a maximum concentration ymax=0.17*x−1, wherein y is the trivalent cerium concentration in mole % relative to the A element, and wherein x is the height or diameter (H) in mm, wherein the garnet type A3B5O12 luminescent material is configured to convert at least part of the light sources light into converter light;
• one or more heat transfer elements in thermal contact with at least one of the side faces;
• and
• a reflector configured to reflect light sources light escaping from the elongated luminescent body back into the elongated luminescent body, wherein the elongated luminescent body is configured between the light source and the reflector.