Lighting optical system and exposure apparatus

A lighting optical system comprising:

• a light source having a plurality of light-emitting elements configured to emit light from light-emitting surfaces, respectively, the plurality of light-emitting elements being aligned with each other in a direction in which the light-emitting surfaces spread;
• a relay optical system configured to convert a luminous intensity distribution of light emitted from each of the light-emitting elements into an irradiance distribution;
• an optical integrator having a plurality of wavefront splitting elements arranged in parallel to each other, the plurality of wavefront splitting elements being configured to wavefront split irradiated light through the relay optical system and to transmit the wavefront split light as a plurality of pencils of light rays;
• and
• a condenser optical system configured to superimpose the plurality of pencils of light rays on each other on a surface to be irradiated, wherein
• the relay optical system is configured to project and superimpose a plurality of the converted irradiance distributions on each other on an incident surface of the optical integrator.