RES Square lenses were designed & optimized for Luxeon Rebel series of LEDs. The lens material is an optical grade PC with high UV and temperature resistance (120°C/248°F) that allows use of high current and temperature conditions. RES Square lenses offer the best available optical efficiency, up to 90%, with an extremely good cutoff of light. These lenses also feature an integrated holder, fastening to heat sink with a PU foam adhesive tape of automotive grade. We advise customer to ensure the suitability and sufficiency of the bond in the end product. For example, mechanical stress, vibration and holes on the surface of the circuit boar weaken the strength of the tape. Please check fastening details from this link: (http://www.ledil.com/datasheets/DataSheet_TAPE.pdf)RES Square lenses have compact dimensions of 21.6 x 21.6 mm. Its square form enables easy build of matrix without any gaps between lenses.