3 Modes with Custom Timer: DIY hour & minute of DAY mode, NIGHT mode, 24/7 mode. Seaoura aquarium light provide LED time clock display system allowing you to program a flexible automatic start & end lighting schedule of sunrise, daylight, sunset, moonlight and off. Simulate natural daily light for your tank based on the local time you set. Time Memory Function: A replaceable battery is featured in the fish light controller to keep the passage of time even if the power is cut off unexpectedly. The aquarium planted light will follow the schedule timely when power restored after a tank cleansing or a blackout. No need to set and calibrate the timer repeatedly.