Conventionally, there is known an alarm illumination device which gradually increases the brightness of a light source from a predetermined time before a preset wake-up time such that a sleeping person can be comfortably awakened at the wake-up time (see, e.g., Japanese Patent Application Publication No. H4-264289). Also, there is known an illumination device which gently changes illuminance from low illuminance to medium illuminance, and rapidly changes illuminance from medium illuminance to high illuminance by using light of at least three types of illuminance, i.e., low illuminance, medium illuminance and high illuminance (see, e.g., Japanese Patent Application Publication No. H7-318670). According to the illumination device, it is possible to cause the biological rhythm of the sleeping person to enter into an active phase while guiding the sleep state of the sleeping person from a deep state to a shallow state.
However, in general, since many people get up after the consciousness is gradually awakened, it takes some time until they actually get up from waking up although there are individual differences. Accordingly, for example, as in the above-mentioned illumination device, when rapidly changing illuminance from medium illuminance to high illuminance, a person who has not been sufficiently awakened during the illuminance change from low illuminance to medium illuminance may feel uncomfortable because of the rapid illuminance change thereafter.