Fahrenheit 451

What do you think Montag means when he says his coworkers' faces were sun burnt by "a thousand real and ten thousand imaginary fires?"

Montag and his coworkers are firemen who burn books in a society where books are forbidden. So, when they do this, when they throw all of these books into the fire, their faces are lit and sunburnt by these real fires they made, as well as the ones found in the books themselves.