A light source comprising a light engine (10), especially with at least one LED and/or at least one laser light emitting element, and further comprising a light guide (11) and an out-coupling structure (12) is proposed. By this, a flexible scheme to tailor the source size and radiation characteristic of an LED- or laser based system is provided. The size and the position of the out-coupling structure (12) can be chosen to be comparable to the size and position of the filament or arc of a conventional light source like an incandescent-, halogen- or gas discharge burner. The disclosed LED/laser light source is retrofit from an optical point of view so that it can replace a conventional light source like an incandescent-, halogen- or gas discharge bulb or burner in an illumination device.