Work only with CRT screens (=> don't work on modern LCD!!).
In fact the electronic beam hits a sensor in the pen, and can determine where is the spot on the screen.
It is not really cute to use. It might not work on all screen resolutions: 320x256 in PAL (320x200 in NTSC) should work, even in overscan, but with interlace, the lightpen is not able to make difference between odd or even lines.
With higher resolutions, a lightpen is not enough precise to draw anything.
Mouse or tablet are done for that job.
That why lightpen is not really usefull on Amiga...
