When light-curable adhesives cure under either UV or visible light, cross-links form between polymer chains. This pulls the chemical chains closer to each other very rapidly. We typically see 1 to 2% linear shrinkage, which could translate into 2 to 5% volumetric shrinkage. This may stress some plastics or optical components. There is a relaxation effect, usually over the next few hours or overnight, where the chains relax slightly as they rotate into an optimum alignment. Polymer chains like to spoon together and snuggle. If they are at odd angles to each other, they still touch, but you want to find that alignment where they are in the same direction and bending the same way. Chemical bonds can stretch and spin around their axis, allowing for this relaxation. It is also good to note that products with a low modulus stretch easier under stress than products with a very high modulus, which do not stretch much at all. Silicones on one extreme can have a modulus as low as 300 psi, whereas epoxies can have a modulus as high as 2,000,000 psi. Many UV-curable adhesives are urethane acrylates, which can have a wide range of modulus values. Your product data sheet should indicate this value.