1. Glazing in a roof facing north, with a pitched roof sloping from the window-head on the southern side. In e.g. a factory, a series of north-lights is often formed with valleys between the bases of the north-lights and the sloping roof, so in section the roof resembles a jagged saw (hence sawtooth-roof).
2. Any large window facing north in e.g. an artist's studio.
"north-light." A Dictionary of Architecture and Landscape Architecture. . Encyclopedia.com. (August 20, 2018). http://www.encyclopedia.com/education/dictionaries-thesauruses-pictures-and-press-releases/north-light
"north-light." A Dictionary of Architecture and Landscape Architecture. . Retrieved August 20, 2018 from Encyclopedia.com: http://www.encyclopedia.com/education/dictionaries-thesauruses-pictures-and-press-releases/north-light