Skylights are light transmitting fenestration (products filling openings in a building envelope which also includes windows, doors, etc.) forming all, or a portion of, the roof of a building space. Skylights are widely used in daylighting design in residential and commercial buildings, mainly because they are the most effective source of daylight on a unit area basis. An alternative to a skylight is a roof lantern. A roof lantern is a daylighting cupola that sits above a roof, as opposed to a skylight which is fitted into a roof's construction. Roof lanterns serve as both an architectural feature and a method of introducing natural light into a space, and are typically wooden or metal structures with a number of glazed glass panels.