A light-emitting product (for example, a flashlight) includes a first housing includes a light source for emitting light and a lens system that is adjustable in position relative to the light source. The second housing can be attached to the first housing and includes a power source for the light source. When the first housing and the second housing are attached, the first housing and the second housing can be moved relative to each other to adjust the position of the lens system relative to the position of the light source to focus the light from the light source.