These headlights look awesome in my opinion and really bring the cosmetics of your Mustang to a new level. They do have a smoked lense, so the night projection of the light isn't super bright but it is similar to stock.
A lot of our customers do run HID's in this particular headlight, we've seen success with a low output 35W HID set up. However, we still don't recommend it. If you do run HID's we can't warranty them if something goes wrong (That the HID's could have caused)! They're designed for a certain heat range output, so an upgraded HID could damage the lens or something a long those lines.
I hope this helps! Please let me know if you have any questions or need some assistance. Our Mustang Experts are here Monday-Friday from 9AM-9PM EST and Saturdays from 9AM-5:30PM EST. If you want to hit them up, their number is 866.727.1266.