An illumination device includes a base, a light-emitting module, a first layer, and a second layer. The light-emitting module is disposed on the base for generating a progressive-type light-emitting intensity. The first layer encapsulates the light-emitting module. The second layer encloses the first layer. The second layer has a progressive-type thickness corresponding to the progressive-type light-emitting intensity, and both the progressive-type light-emitting intensity and the progressive-type thickness are decreased or increased gradually, thus the progressive-type light-emitting intensity can be transformed into the same light-emitting intensity through the progressive-type thickness of the second layer.