has recesses 28 in which the leds 24 are located in order to provide a reasonably uniform diffuse light for all the keys of the array leds are placed in the recesses 28 fig4 in the key mat at a number of locations 29 fig5 for the leds 24 fig4 6 mainly between the keys where they do not interfere with mechanical operation of the keys the key mat has switch protrusions 34 located respectively in register with each key cap 14 and transparent intervening parts 40 have been attached to the key caps between the key cap and the switch protrusion 34 the depression or actuation of the key results in the intervening part 40 relaying the actuation force to the key mat by its switch protrusion 34 deforming the key mat 32 to depress the switch 36 the transparent intervening parts 40 also guide light from the key mat to the holes 18 to prevent the ingress of dirt through the tiny holes the engraved character may be filled with a translucent resin as illustrated in fig3 the translucent resin may provide the additional effect of acting as a diffuser for the light giving an increased angle of visibility the resin is preferably treated such that it will fill entirely the engraved character.