If you’ve ever been lucky enough to travel in India and visit famous sites like the Taj Mahal or the Sidi Saiyyed mosque, you probably noticed beautiful, intricate window screens called Jali among the many incredible sights. Carved out of stone in geometric or plant-like designs, jali became fixtures in Islamic and Hindu architecture as early as the 6th century in temples, but by the 17th century they were also being frequently used in a variety of domestic and public spaces in India.

The obvious appeal of jali is in the beauty and decoration that they add to the buildings and sacred spaces where they’re featured.

Just as the stained glass windows in Christian churches cast beautiful colored light when hit with sunlight, jali create an intricate display wth the shadows they cast. Not just for windows, ornamental jali were used as room dividers to provide privacy, and as decorative elements on interior and exterior spaces like railings and stairwells.

The type of stone used to construct jali was often determined by the specific building and its geographical location, with marble and red sandstone being among the most popular. Indoor jali that were protected from the elements were sometimes surrounded by decorative inlays made with semi-precious stones, and the Taj Mahal in particular features amazing examples of this ornamental work.

As if being beautiful wasn’t enough, jali also serve a practical purpose. When placed in outside windows,jali function as Air Conditioning devices, and have been keeping buildings cool in some of the world’s hottest places long beforecentral air conditioning systemsand electricity were available.

The Science Behind JaliCreating a window that’s partially covered instead of completely open, jali serve the immediate function of blocking some sunlight from entering a building, yet allowing air to pass through. Unlike modern day window screens that are usually quite flat, jali were constructed with a ratio between the thickness of the screen and the size of the openings designed to create a specific amount of overhang and cut down the sunlight passing through the screen without completely blocking out the light.

In addition to keeping the hot sun from penetrating inside, the specific design elements in jali use principles of physics to actually cool the air that moves through them. When air passes through a small hole its speed increases, so a breeze passing through a jali screen would be more noticeably felt inside than if the wind was passing through an open window. By minimizing direct sunlight and maximizing the effect of a breeze, jali are cooling marvels disguised as a beautiful decorative element. In effect it is a simplistic "air conditioner" with no maintenance and no electricity.

While there are many existing buildings in India that feature jali, the privacy concerns of modern day means they haven’t been frequently used in more recently constructed homes or buildings. But as environmentally friendly solutions to keeping modern conveniences become more necessary, it’s possible that jali, the beautiful decorative element that provides simple, energy-free cooling, could make an architectural comeback.