Aquaristic/terraristic dimmer controls lights in aquarium/terrarium. It smoothly fades in lights in the morning and smoothly fades out in the evening, which simulates sunrise and sunset, because fish could be shocked and die by sudden activation of lights. Dimmer starts to fade in the bulbs in adjusted time (increases the power) and after full slope (15 minutes) switches to fluorescent tube because of power saving. Then tube lights until adjusted time for turning off, when the device switches back from tube to bulbs, which slowly fades out then (time for fade out is the same as for fade in). With this the cycle ends and dimmer waits for time for fade in.