What is "roshandan"

A roshandan ( Hindustani: रोशनदान or روشندان) is a feature of many dwelling structures in North India and Pakistan that is a combined skylight and ventilating window. Roshandans are usually located high on a room's walls, and often on top of windows. They are essentially smaller windows that swivel open when needed. Smaller roshandans are sometimes called roshandanis. The high location of roshandans means that, for part of the summer (except for the months when the Loo winds blow in the region), they can be kept open to allow heated air just below the ceiling to escape while retaining relatively cooler air inside. In wintertime, they are kept shut and used purely as skylights.