glass each casing contains a row of light guides 706 extending end to end along its longitudinal length each casing further contains a respective metal jacket 702 of semi circular or crescent cross section which supports the light guides a plurality of heat spreaders 703 are mounted to the metal jacket 702 the light guides 706 are positioned between the heat spreaders 703 so that each end of a light guide is adjacent a heat spreader thus in fig2 c there is a first light guide 706 a between first and second heat spreaders 703 a 703 b and a second light guide 706 b between the second 703 b and third 703 c heat spreaders the heat spreaders 703 are in thermal communication with the metal jacket 702 the heat spreaders 703 have two opposite sides and an led 705 mounted on one or both sides as shown in fig2 c and fig2 d surface mount type leds 705 are mounted via substrates 710 to the heat spreaders 703 the heat spreaders 703 are mounted to the metal jacket 702 by one or more screws 704 the heat spreaders 703 serve to the support the leds and conduct heat from the leds to the metal jacket 702 the metal jacket 702 plays an important role in the design it serves not only as a mechanical support for the light guide tubes and leds but also for dispersing the heat generated by leds quickly the leds are mounted to the metal jacket via a heat spreader which has a higher thermal conductivity than the metal jacket for example the heat spreader may be made of copper and the metal jacket of aluminum this facilitates rapid conduction of the heat from the led through the heat spreader to.