An LED-based photolithographic illuminator with high collection efficiency is disclosed. The illuminator utilizes an array of LEDs, wherein each LED has an LED die and a heat sink. The LED dies are imaged onto the input end of a homogenizer rod to substantially cover the input end without inclusion of the non-light-emitting heat sink sections of the LED. A microlens array is used to image the LED dies. The collection efficiency of the illuminator is better than 50% and the illumination uniformity at the output end of the light homogenizer is within +/−2%.