Amstrad LP-1 light pen

The LP-1 Lightpen by Amstrad

The LP-1 is the official Amstrad lightpen (with software from Amsoft, and hardware from Trojan).

The CAD-MASTER seems to be the same hardware (but marketed directly by Trojan, and with different Software included).

Technical

Connects to the Joystick port (not to the Lightpen input on the Expansion Port).

The pin-outs are unknown?

One pin is probably used as Light Sensor, but which?
Other pins might be used as power supply (needing to drag some pins HIGH and others LOW by software) (or does it contain a battery)?
- Software seems to indicate it has a battery..?
  - Rather not: The spectrum version connects to the spectrum EAR socket and to a huge 9V battery (the amstrad version doesn't seem to have any such 9V plug)
There seems to be no additional button (like on Light-guns)?
According to the advert and package, the light pen works with colour monitor only ("pour moniteur couleur uniquement"), ie. not with green screens.