Do any have any info on a Light Pen from Sanyo/Hal, have software for it on a cart,
but seems to go with a Light Pen. Which I have never seen, the Pen from Philips or a mouse do not work with it.

I've never seen a lightpen for real either, but there is support for it in the MSX2 BIOS.

On MSX Banzai! you can see a photo of a Sanyo MSX2 with lightpen.

I have the Sanyo Light Pen Unit. It has (MSX1) software built-in. It comes with some graphic commands enabling to draw two types of line and paint an area like on SCREEN5 or higher on SCREEN2 with a reduced color spill. There is probably a rom-image of the program roaming the net. A PDF of the manual can be found on www.hansotten.com somewhere in the MSX section.

As GuyveR800 said, there's support for it in the MSX2 BIOS. The PAD(8) to PAD(11) functions make Light Pen access easier. IIRC the coordinates are slightly off-center though. The internal soft has some offset method to get the correct coordinates.

Would there be any interest in a music player that supports a light pen for operation?

If anyone can explain what a lightpen actually DOES (how to use it), that'd be helpful ^^;

I really have no idea...

The light pen is capable of returning the coordinates it 'looks' at when it's pressed on the screen, updating them as it moves until the light pen is released from the screen.

To compare it with something more known... it's like pushing on a touchpad. it only returns coordinates when it's sensed. The light pen can only 'see' the coordinate when it's pressed on the screen.