My hamster freezes when I turn on the lights. Why does she do that?

Hi! Daisy sounds like a very healthy, normal hamster! Hamsters are crepuscular, which means they will be most active at dawn and dusk. Hamsters are also prey species, and have an innate drive to avoid predation. Daisy’s instincts tell her to be still and/or hide if she suspects she may be in danger. The abrupt switching on if the lights likely startles Daisy and until she can assess the situation to be sure she is safe, she will freeze to avoid detection by a possible predator, just like you said. So this is just natural self preservation instinct, and nothing to be worried about. However, it may be a bit stressful to Daisy, so try to minimize how often you turn the lights on during the night. If you’d like to observe her in the dark, consider getting a red or blue light bulb (from petco or other pet store, often in the reptile section) that will allow you to see her, but should disturb her.