Main difference in the wiring of an electric bulb and a socket for using an electric iron:
An earth connection is given to the socket for an electric iron, whereas no earth connection is given to an electric bulb.
It is because earth connections are given to only those appliances that have metallic body, draw heavy current and can be touched. Therefore, an electric iron is provided with earth connection.
However, earthing is not done with electric bulbs because we hardly touch them when they are on.