light unit 2 is a exit sign light unit for this purpose the distal side 12 b of the lens cover 12 is provided with the word exit 14 which is made from a red transparent material layer in other words an additional layer 14 having the shape of the word exit is applied to the distal side 12 b of the lens cover 12 this additional layer 14 acts as a localised color filter as can be seen from fig1 a the locations of the individual letters of the words exit 14 coincide with some of the locations of the dots 16 the locations of the letters of the word exit 14 and the location of the dots 16 may be chosen independently from each other fig1 b shows an interior aircraft led light unit 2 in accordance with another exemplary embodiment of the invention with the interior aircraft led light unit 2 being shown in an exploded view as well the interior aircraft led light unit 2 of fig1 b corresponds to the interior aircraft led light unit 2 of fig1 a with the exception of the word exit 14 being omitted in this way the interior aircraft led light unit 2 of fig1 b does not convey any signalling information it rather serves a general illumination purpose and is provided as a cabin illumination light unit again the pattern of dots 16 is a random pattern of dots distributed over the distal side 12 b of the lens cover 12 a method of calibrating the interior aircraft led light unit 2 of fig1 b which takes place during the manufacturing of the interior aircraft led light unit 2 will be described as follows during.