A tooth whitening method applies a light transmitting oxidizing composition to teeth in an oral cavity, after which a hand-held LED light source with a light transmitting lens and a cup forming a chamber having an open end is moved over the teeth so that the cup distributes the oxidizing composition while the teeth are exposed to light transmitted through the lens. This not only ensures intimate contact of the teeth with the oxidizing composition, but also maintains a more or less constant spacing between the light source and the tooth surfaces for optimum results. A sealant is then applied to the teeth to resist moisture contamination of the oxidizing composition.