Asymmetric carbon atoms confer optical activity to the sugars. When a polarised light passes through a solution showing optical activity, the plane of the light is rotated to the right or the left. If it is rotated towards the right the sugar (compound) is called dextrorotatory (denoted as d or +), and if it is rotated towards the left the sugar (compound) is called laevorotatory (denoted as l or −). If equal amounts of dextrorotatory and laevorotatory isomers are present in the mixture, then there is no optical activity. Such a mixture is known as racemic mixture.