Illuminance changed

The Illuminance changed trigger fires after a light level reading changes. The morning sun shining into a bedroom, a desk lamp switching on, or clouds shading a patio all show up as illuminance changes. Use the threshold type to filter which changes matter to your automation.

The threshold type controls where the new reading must land for the trigger to fire. You can require the new value to be above a level, below a level, within a range, or outside a range. The entity that changes must be an illuminance sensor. You can use a number entity with the illuminance device class as the threshold value.

Use Illuminance changed to log light trends, react when a room becomes noticeably brighter or darker, or coordinate shades and lighting based on ambient conditions.

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 Illuminance 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 sensor is in (like your living room or backyard). 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 Illuminance 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 value in lux, pick a sensor entity, pick a number entity, or pick 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. For how an automation is built in YAML, refer to Automations in YAML.

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, Illuminance changed is referred to as illuminance.changed. A basic example looks like this:

trigger: illuminance.changed
target:
  entity_id: sensor.living_room_illuminance
options:
  threshold:
    type: above
    value:
      number: 500

This fires whenever the living room illuminance sensor reading moves to a value above 500 lx. To fire on any change regardless of direction or value, use type: any and omit value.

To fire only when the new reading is within a comfortable reading range:

trigger: illuminance.changed
target:
  entity_id:
    - sensor.living_room_illuminance
    - sensor.office_illuminance
options:
  threshold:
    type: between
    value_min:
      number: 300
    value_max:
      number: 750

This fires whenever any of the illuminance sensors changes to a value within the reading range (300 lx to 750 lx).

To use a number helper as a dynamic threshold that you can adjust without editing the automation:

trigger: illuminance.changed
target:
  entity_id: sensor.living_room_illuminance
options:
  threshold:
    type: above
    value:
      entity: input_number.brightness_alert_threshold

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 illuminance sensor behind that target.

• Entity: one specific illuminance sensor, such as sensor.living_room_illuminance.
• Device: every illuminance sensor that belongs to a device.
• Area: every illuminance sensor in a room or area.
• Floor: every illuminance sensor on a floor.
• Label: every illuminance sensor 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 reacts, the trigger variable identifies the entity that made it react. This is useful when a target contains multiple entities, such as a device, area, floor, or label.

The following trigger-specific variables are available:

• trigger.entity_id: Entity ID of the entity that made the trigger react.
• trigger.from_state: Previous state object of that entity.
• trigger.to_state: New state object of that entity.
• trigger.for: Timedelta object of how long the trigger criteria were met, if applicable.

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

The trigger variable describes the entity that made the trigger react. It doesn’t contain all the entities of the target.

Good to know

• Use a sensor with the illuminance device class.
• Illuminance is measured in lux (lx). For reference: a brightly lit office is around 500 lx, indirect daylight is several thousand lx, and direct sunlight can exceed 100,000 lx.
• If you use an entity as the threshold, it must use lx as its unit. If it has a different unit, or no unit, the trigger doesn’t react.
• Number entity support applies to threshold values, not to the target being checked. The number entity must use the illuminance device class.
• The threshold type controls both the direction and the landing zone of the change. Use Above or Below to filter by direction, In range to fire only when the new value is inside a range, and Outside range to fire only when it escapes a range.
• Use Any change to fire on every change regardless of direction or where the new value lands.
• To react only when an illuminance reading first crosses a specific level, use Illuminance crossed threshold instead.

Try it yourself

Ready to test this? Go to Settings > Automations & scenes, create a new automation, and add this trigger. Save the automation, and then make the trigger react. For example, change the state of the targeted 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], turn on a light that the trigger monitors, or change its brightness. To check whether the automation ran, open its traces.

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: close the blinds when the patio gets too bright

When the patio illuminance sensor reports a sudden increase in brightness, close the patio blinds to keep direct sunlight off the furniture.

• Trigger: Illuminance changed
  • Target: Patio illuminance sensor
  • Threshold type: Above 30000 lx
• Action: Close cover
  • Target: cover.patio_blinds

alias: "Close patio blinds in bright sunlight"
triggers:
  - trigger: illuminance.changed
    target:
      entity_id: sensor.patio_illuminance
    options:
      threshold:
        type: above
        value:
          number: 30000
actions:
  - action: cover.close_cover
    target:
      entity_id: cover.patio_blinds

Still stuck?

To find out why the trigger didn’t react, make the change that it should react to, and then open the traces of the automation. If the automation didn’t run, there’s usually no trace, but some triggers record a Did not trigger trace. For details, refer to Testing automations. For common problems and their solutions, refer to Troubleshooting automations.

If that doesn’t help, 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:

• Illuminance crossed threshold: Triggers when one or more illuminance values cross a threshold.

• Light level detected: Triggers when one or more light sensors start detecting light.

• Light level cleared: Triggers when one or more light sensors stop detecting light.