why is a halo used in most christian art works depicting the holy or sacred figures?

If I remember correctly, that goes back to the sun worshipping religions.

(Edit)

Here it is. I found a reference.

http://www.trivia-library.com/a/what-was-the-origi...

What Was the Origin of the Halo? Surprisingly, the halo is both pagan and un-Christian in origin. Many centuries before Christ, natives decorated their heads with a crown of feathers. "They did so to symbolize their relationship with the sun-god: their own 'halo' of feathers representing the circle of light that distinguished the shining divinity in the sky. Indeed, people came to believe that by adopting such a 'nimbus' men turned into a kind of sun themselves and into a divine being."

Later in history, the Roman emperors who began to think of themselves as divine beings wore a crown in public to imitate the sphere of light from the sun.

The need to preserve art objects also added to the development of the halo. "Statues were kept not in museums but in the open. Therefore they were subject to deterioration through various causes. To protect them from the droppings of birds, the rain and the snow, a circular plate--either of wood or brass--was fixed upon their heads!"

I am not sure what the halo is supposed to represent, but religious symbols are often taken from other places and adapted and their meanings change over time.

For example, Hitler took a rune from Hindu religion, and now it is one of the most hated symbols ever.

Everyone borrows signs and art and symbols and traditions from everywhere else. It was a way of getting peoples to adapt to having a new religion. When the christians wanted to convert the Celts they used celtic holidays and just changed them to Christian ones, Christmas is the biggest example.

Originally horns were depicted as a sign of divinity but later it was changed to the halo and horns were made into a sign of the Christian anti-god to try to get rid of the Pagans.

Blessed Be )O(

It goes back to the Greeks. They were the first ones to incorporate the 'crown,' as a symbol of Deity.

It represents the light of God shining upon them.

Nimbus

Try this link

http://www.newadvent.org/cathen/11080b.htm

I hope you'll read through it without bias.

I think it is worship of the brain basically.