Here is the deal with the LED's: we NEVER see the LED's clearly lit or blinking in either ESB or ROTJ. However, there are two or three promotional stills (I am sure of an ESB still and a Preproduction 2 still) that show one of the LED's lit while the rangefinder is down.
Also, at various conventions, Jeremy Bulloch demonstrated the blinking pattern of the LED's while the rangefinder is down.
And yes, many fan-made helmet LED's tend to be too tall. The LED's on the real helmet look more squatty.