Not my ball, not my home, not my game.
The Lightpen was really used mostly in Point Of Sale, Medical, Industrial and Mobile computing systems. I admit it is not used in 100% of the systems out there, but it is used. In fact, companies such as this one [link|http://www.inkwellsystems.com/|[link|http://www.inkwellsystems.com/|http://www.inkwellsystems.com/]] seem to be in the business of selling Lightpens and seem to stay in business. If nobody uses Lightpens, then how does this company stay in business since 1983?
Click on that company's technical button and read:
Light pens are perfect for applications where desk space is limited, in harsh workplace environments, and any situation where fast accurate input is desired.
Does that, or does that not change the user experience when in some conditions it may be better to use a Lightpen instead of a mouse? Such as in an assembly plant with little or no deskspace to roll around a mouse, or perhaps a point of sale system on a sales counter?