A couple points:
1) Just want to make perfectly clear you know I'm not Robert Zubrin. because while that would be dope it just ain't so. 2) Your 532W number is presuming 6 nines of efficiency. Reality begs to differ. I think we're still pretty squarely in "holy shit death ray" territory, particularly considering some process or other needs to turn mass into photons and it's going to be terrifying. We're going from (Niagara Falls is 2400 metric tons per second) To ...at which point I don't even care where it's pointed - the engine of doom necessary to drive the conversion scares the shit out of me. I'm almost certain I've seen this movie...Your question about what it would look like is entirely valid, and I can't give you an answer better than "bright."
about 3,780 metric tons per second, equivalent to a modest river 120 meters wide by 30 meters deep, following along at a leisurely 1 meter per second
an exhaust velocity of 60,000 meters per second
Another fun thought experiment would be to imagine what would happen if you pointed this "engine" at another, earth sized planet.