I am swapping out all the lights for sealed unit lights. I cannot find one with a white light over the license plate, and noticed that my XP trailer had no light there either.
If another Texan posts pretty quick they should know. Otherwise you might check the Texas Highway Patrol web site for regs in your state. They will vary from location to location across the country.
just as a common sense it would be good to have it there anyway. every trailer I have seen has it but then again I live in Virginia the nazi state where everything is illegal!