An LED module is formed using a method of mounting secondary lens arrays over light-emitting diode arrays on a printed circuit board. In the LED module, a lens array assembly is mounted to a printed circuit board. The lens array assembly comprises a silicone free form lens array which is mounted in a lens holder by aligning markings on the lens holder with markings on the free form lens array. The lens array assembly is correctly positioned, in an x-y plane, on the printed circuit board by the engagement of positioning pins formed on a surface of the free form lens array with corresponding recesses formed in the printed circuit board and is retained in the correct position by clips integrally formed with the lens holder. The positioning pins are shaped to allow for thermal changes due to the operating temperature range of the LED module.