Hmmm. I thing you ought to go look up ubiquitous. It means its now everywhere and it changed the way people use computers forever. Light pens are not ubiquitous. You're off topic. Name innovations that appeared first on the PC that now appear on *all* macs and pcs and unix machines - IOW, something now so fundamental that you'd never consider getting a computer without one. Like CD ROM capable drives (these days most people are going to insist on DVD-ROM at least).
Not like light pens.