Light brightness changed

The Light brightness changed trigger fires after the brightness of a light entityAn entity represents a sensor, actor, or function in Home Assistant. Entities are used to monitor physical properties or to control other entities. An entity is usually part of a device or a service. [Learn more] changes. Use it to react to dimming, like adjusting a fan speed as you brighten the room, or logging changes to a dashboard graph. Brightness is measured as a percentage of full brightness, from 0 to 100.

The threshold type controls where the new brightness must land for the trigger to fire. You can require the new brightness to be above a level, below a level, within a range, or outside a range. You can also select Any change to fire on every change.

Using this trigger from the user interface

If you prefer building automations visually, Home Assistant walks you through this trigger step by step. You pick what to watch, tweak a few options, and save. No YAML knowledge required.

To use Light brightness changed in an automation:

1. Go to Settings > Automations & scenes.
2. Open an existing automation, or select Create automation > Create new automation.
3. In the When section, select Add trigger.
4. Select what you want to monitor. Under By target (see Targets), pick the area your light is in (like your living room or bedroom). You can also select a device, a specific entity, or a label. When you target multiple entities (via area, label, or multiple entity selections), the trigger fires whenever any of them changes.
5. From the triggers shown for that target, select Light brightness changed.
6. Under Threshold type, configure what kind of change fires the trigger:
   • Select Any change to fire on any change, regardless of direction or new value.
   • Select Above or Below and enter a value to fire only when the new reading is above or below that value.
   • Select In range and enter a lower and upper bound to fire only when the new reading falls inside the range.
   • Select Outside range and enter a lower and upper bound to fire only when the new reading is outside the range.
   • For each option, you can enter a fixed percentage (0–100%), pick a sensor entity or a number helper entity as the threshold.
     • If you don’t have a number helper, you can create one by selecting Create a new number helper.
7. Select Save.

Options in the UI

Using this trigger in YAML

If you work directly in YAML, or you want to know exactly what Home Assistant does under the hood, this section has the technical reference. It lists the field names you use in YAML, their types, and which ones are required.

In YAML, put the settings that are specific to this trigger under options. Keep target, if the trigger uses one, and general settings such as id, alias, enabled, and variables at the top level, next to trigger.

When this trigger starts an automation, it passes data about what happened to the automation. You can use this trigger data in the templates of your conditions and actions. To see which data is available, refer to Trigger data in templates.

In YAML, refer to this trigger as light.brightness_changed. A basic example looks like this:

trigger: light.brightness_changed
target:
  entity_id: light.living_room
options:
  threshold:
    type: above
    value:
      number: 10

This fires whenever the living room light’s brightness changes to a value above 10%. To fire on any change, use type: any and leave out value.

Options in YAML

Targets of the trigger

This trigger requires a target. The target is the object that Home Assistant will watch. You can select a single entityAn entity represents a sensor, actor, or function in Home Assistant. Entities are used to monitor physical properties or to control other entities. An entity is usually part of a device or a service. [Learn more], a device, an area, a floor, or a label as a target, and Home Assistant will watch every matching light entity behind that target.

• Entity: one specific light entity, such as light.living_room.
• Device: every light entity that belongs to a device.
• Area: every light entity in a room or area.
• Floor: every light entity on a floor.
• Label: every light entity that shares a label.

You can also select different target types in one trigger. For example, you can add a specific entity and an area as targets in the same trigger to monitor both of them at once.

To learn which entities Home Assistant includes for a device, area, floor, or label, and how it handles several entities, refer to Automation targets.

Trigger variables

When the trigger fires, the trigger variable identifies the entity that caused it to fire. This is useful when a target contains multiple entities, such as a device, area, floor, or label.

The following trigger-specific variables are available:

For example, use {{ trigger.to_state.name }} in an action to include the name of the entity that caused the trigger in a notification.

The trigger variable describes the entity that caused the trigger to fire; it does not contain all entities resolved from the configured target.

Good to know

• The threshold type controls which changes fire the trigger. Use Above or Below to fire only when the new brightness is above or below a value, In range to fire only when it’s inside a range, and Outside range to fire only when it’s outside a range. Use Any change to fire on every change.
• To react only when brightness first crosses a specific level, use Light brightness crossed threshold instead.
• A light that is off has no brightness value, so turning a light off does not fire the trigger. Turning a light on does fire the trigger if the new brightness matches the threshold.
• If you use an entity as the threshold, it must report its value in percent (%). An entity with a different unit, or no unit, is ignored and the trigger does not fire.

Try it yourself

Ready to test this? Go to Settings > Automations & scenes, create a new automation, and add this trigger. Save the automation, then change the state of the targeted entity to watch the trigger fire on your actual entitiesAn entity represents a sensor, actor, or function in Home Assistant. Entities are used to monitor physical properties or to control other entities. An entity is usually part of a device or a service. [Learn more].

More examples

Real scenarios where this trigger fires in automations and scripts. Copy any example and adapt it to your setup. In the visual editor, select the UI options listed in the example when they are available, or paste the YAML code.

Automation: sync a ceiling fan speed to the ceiling light

When you dim the ceiling light below 10%, slow the fan down too. A classic “scene mood” automation that keeps the room coordinated.

• Trigger: Light brightness changed
  • Target: Living room ceiling light
  • Threshold type: Below 10%
• Action: Set fan speed
  • Target: Living room fan
  • Percentage: 20%

alias: "Match fan to ceiling light"
triggers:
  - trigger: light.brightness_changed
    target:
      entity_id: light.living_room_ceiling
    options:
      threshold:
        type: below
        value:
          number: 10
actions:
  - action: fan.set_percentage
    target:
      entity_id: fan.living_room
    data:
      percentage: 20

Still stuck?

The Home Assistant community is quick to help: join Discord for real-time chat, post on the community forum with the trigger you’re using and what you expected to happen, or share on our subreddit /r/homeassistant.

Related triggers

Explore related triggers:

• Light brightness crossed threshold: Triggers when the brightness of one or more lights crosses a threshold.

• Light turned on: Triggers when one or more lights turn on.