Here is a list of events that can be used in automations created in Hue Essentials:
Day and night
Event that will run at either sunset or sunrise. This uses the bridge location to determine whether it is day or night. Days can also be selected.
Time
Event that will run at a configured time. Time can be randomised. If the repeat option is enabled you can select the days this Automation should repeat on. If the repeat option is disabled this automation will only execute once.
External
Use this event to be able to start the automation externally. For example, from another automation, widgets, quick settings tiles, Siri Shortcuts, other apps like Tasker, or manually using the API.
After saving the automation, the automation can be started from other places in Hue Essentials or outside of Hue Essentials.
More details on creating such an automation: Automation that can be triggered externally
Device state
Event that will run when the state of a device changes. For example, when a light is turned on, when a button is pressed, when motion is detected, when a device temperature changes to above a certain level, or when it becomes dark.
For more information about device state automations see: Device state automations (smart switches, motion sensors, lights, and plugs)
To create an automation for a device, go to your device on the devices screen and create an automation there.
Group on state
Event that will run when a group is switched on or off. This event can be triggered when any of the lights in a group are switched on, or all of its lights are switched off. You can select whether it should trigger on an on or off event.