Actinic keratoses can become quite obvious and many patients will go to whatever lengths they need to to get rid of them. Light treatments alone can lift pigment, but you need chemical agents to truly obliterate the abnormal cells. Blu U, Vbea and other light sources are usually combined with a solution called levulinic acid. The solution is applied to the skin and is absorbed by the cells of the actinic lesions. Once the light or laser is used, it "turns on" the destruction mechanism of the solution.. The solution is heavily absorbed by abnormal cells, so you get the benefit of the destruction of the actinic keratoses while not damaging the healthy skin. There is some downtime associated with pdt and you will need to stay completely out of the sun for a two day period because the solution stays active for a while even after it is removed.
If you are referring to the combination of Blu-U and levulan, it is an excellent option for both sun spots and actinic keratosis. More than one treatment may be required especially if you're doing it for cosmetic improvement of the brown sun spots.