[jidoman]

f... im not sure what is a LED ( and the web i use for translate dosent work)
is the piece that write or the piece to erease :) ?
anyway u could do in the same way with the both of them

cut your polys until u have the part and then select only the surfaces (polys) of that part
- know u have two choises
1 - detach ( this way that part will become a new object that dosent have nothing in comun with your pencil and u could asign a material only for that part)
2 - or with that polys still selected use SET ID : ... u choose a number , and then u will
use a single material for your pencil and LED , but your material must be Multi/Sub-Object

hope u understand something if not ask :) see ya