As a keen amateur grower I give my Masdevallias low to medium light levels with dapple shade, remember I grow in a greenhouse not in the home, I have never considered additional supplimentary lighting however I’m sure a lot of growers do (mostly in the home) and you may get help from asking members of the face book group. I’ve realised over the years that my Masdevallias can handle more light then the books tell us, I’ve found that if some of my Massie don’t get good light through the growing season they do not bloom for me (the same as not getting a nighttime drop in temperatures), so if you are thinking of adding additional lighting just be cautious try for about 2-4 hours a day to start with then increase when your happy to up to 8 hours a day, try to keep the lights at about 2′ to 3′ or 61 mm to 91.5 mm above the plants to prevent possible leaf burn.