The phrase "to catch the light" means to be in a position where light shines on something, making it appear brighter or more noticeable. Full definition
These statement earrings will also be in heavy rotation for spring — they are light as a feather & really catch the light in a striking way. (pennypincherfashion.com)
They are quite lovely, and catch the light beautifully. (novica.com)
With a flattering length and intriguing depth, the diamond catches the light at just the right time, creating an elegant and glamorous appeal. (creditdonkey.com)