A device manufacturing method includes conditioning a beam of radiation using an illumination system. The conditioning includes controlling an array of individually controllable elements and associated optical components of the illumination system to convert the radiation beam into a desired illumination mode, the controlling including allocating different individually controllable elements to different parts of the illumination mode in accordance with an allocation scheme, the allocation scheme selected to provide a desired modification of one or more properties of the illumination mode, the radiation beam or both. The method also includes patterning the radiation beam having the desired illumination mode with a pattern in its cross-section to form a patterned beam of radiation, and projecting the patterned radiation beam onto a target portion of a substrate.