So, to answer the question initially stated about safety, it’s unclear. Therefore you should avoid using UV light kits at home, as the research isn’t definitive enough to say that it’s safe. Plus, the ADA has not approved this kind of therapy.
Another potential issue in using UV teeth whitening is that there can be extreme user error, resulting in damage and even burns. The ratio of gel to UV exposure varies from kit to kit, and without the consultation of a dentist, you may not know your threshold for sensitivity. What's more, applying too much gel at one time can result in the gel conducting too much of the heat from the UV light, causing gum burns.