Unlike melee classes, Bright Wizards don't want to run all over the map chasing you. In fact, if they can casually sit back in one place and melt your face off then that is exactly what they're going to choose to do. Your best defense is to continually duck behind rocks, trees, bushes, pillars, walls, anything that you can use to break the Bright Wizard's line of site on your pretty mug. If you're a heavy melee class, then you stand to benefit just as much by getting directly in their face, hitting them often to push back their spells. If you can stand behind them and attack then you are in the safest place, not only interrupting their spells but guaranteeing that you aren't the target.