<p>A method of controlling a spectral property of a light beam includes directing a light beam to a lithography exposure apparatus configured to create a pattern on a wafer; receiving information representative of a spectral property of the light beam; receiving information representative of an optical imaging condition of the lithography exposure apparatus; estimating a characteristic value of the light beam based on the received spectral property information and the received optical imaging condition information; determining whether the estimated light beam characteristic value matches a target light beam characteristic value; and if it is determined that the estimated light beam characteristic value does not match the target light beam characteristic value, adjusting the spectral property of the light beam.</p>
