A mock-up of how the projection could look as results come in
The results of the general election are to be projected on to St Stephen's Tower, which houses Big Ben, for the first time, by the BBC.
The number of seats won by the three largest Westminster parties will be updated over the course of the night.
The images, illustrating the state of the parties, will be beamed from the moment the first result is declared until about 0530 BST the next morning.
The BBC said it was "delighted" with the initiative.
With four days of campaigning left, the latest opinion polls suggest the election remains finely balanced and that a hung parliament - where no party has an overall majority - remains a possibility.
The idea behind projecting the results is to provide a clear and simple source of information and an arresting image.
The projections, which will not carry BBC branding, will be beamed onto the side of St Stephen's Tower, at the Houses of Parliament, which houses the world-famous bell known as Big Ben.
They will provide a running tally of the number of seats won by Labour, the Conservatives and the Liberal Democrats, along with those gained by the smaller parties and independents combined.
In the minutes after polls close on 6 May, the details of an exit poll conducted by NOP/Mori will be beamed onto Big Ben, under an agreement between the BBC, ITN and Sky News.
The results projection, which will be removed after dawn on 7 May, will feature a "winning line", representing the 326 seats that any party will need to win to be sure of an outright victory.
The idea was approved by the parliamentary authorities, responsible for the management of its buildings.
"This is an historic election," said Craig Oliver, editor of the BBC's Election Night programme.
"We're delighted Parliament is joining with the BBC to project the results onto Big Ben for the first time ever."