Prismatic glass shades are made from cast glass characterised by small ridges on the outside surface. It is these ridges that allow the light to be evenly distributed around the fitting and obscure the light bulb. With a history as long as electric light, prismatic light fittings have a timeless appeal. Because of the way that prismatic glass shades throw light, these wall lights make more of the light than those with fabric shades.
Prismatic glass is cast glass, bubbles & small irregularities are features of cast glass and not considered faults.