South Korean scientists have devised a "smart" window that saves energy by automatically switching from summer to winter mode.

The new "smart" window becomes transparent in winters so that it could draw heat from the sun, and starts darkening when it gets hot outside.

In other words, smart windows can prevent the inside of a house or an office from becoming overheated by reflecting back the sunlight in summer; and can keep a building warm by allowing the sunlight to enter get into in winter.

The invention, by the team of scientists from Korea Electronics Technology Institute and Soongsil University, published in the recent issue of journal ACS Nano.

Speaking on their invention, scientists said, "This type of light control system may provide a new option for saving on heating, cooling and lighting costs through managing the light transmitted into the interior of a house."

Scientists made use of a sort of charged particles, called counterions, along with solvents such as methanol to produce the smart window.

The new smart window is capable of switching from cent per cent opaque to fully clear in a few seconds.