Illuminance crossed threshold

The Illuminance crossed threshold trigger fires when a light level reading crosses into a zone you define. A patio sensor crossing above 30,000 lx when the sun comes out, a desk sensor dipping below 200 lx as it gets dark in the office, or a reading escaping that range are all supported.

Use Illuminance crossed threshold to automate shades when the sun gets too bright, turn on lights when a room becomes too dark, or coordinate devices that respond to specific light levels.

When you target more than one entity, the trigger’s Trigger when option controls when it fires.

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 crossed threshold 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 office or patio). You can also select a device, a specific entity, or a label.
5. From the triggers shown for that target, select Illuminance crossed threshold.
6. Under Threshold type, configure the zone the reading must enter for the trigger to fire:
   • Select Above or Below and enter a value to fire when the reading crosses that level.
   • Select In range and enter a lower and upper bound to fire when the reading enters the range from outside.
   • Select Outside range and enter a lower and upper bound to fire when the reading leaves the range (crosses past either bound). For each option, you can enter a fixed value in lux, pick a sensor 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. Under Trigger when (see Behavior), pick Each, First, or All to control how the trigger behaves when multiple entities are targeted.
8. Under For at least, set how long the reading must stay past the threshold before the trigger fires. Leave it at zero to fire immediately.
9. 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, Illuminance crossed threshold is referred to as illuminance.crossed_threshold. A basic example looks like this:

trigger: illuminance.crossed_threshold
target:
  entity_id: sensor.office_illuminance
options:
  threshold:
    type: below
    value:
      number: 200

This fires whenever the office illuminance sensor drops below 200 lx.

To fire when the reading leaves a comfortable reading range (escapes above 750 lx or below 300 lx):

trigger: illuminance.crossed_threshold
target:
  entity_id:
    - sensor.office_illuminance
    - sensor.study_illuminance
options:
  threshold:
    type: outside
    value_min:
      number: 300
    value_max:
      number: 750

This fires whenever any of the illuminance sensors crosses outside the reading range.

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

trigger: illuminance.crossed_threshold
target:
  label_id: outdoor_light_sensors
options:
  threshold:
    type: above
    value:
      entity: input_number.brightness_alert_threshold
  behavior: first

This fires when the first outdoor illuminance sensor crosses above the threshold set in the number helper.

Options in YAML

YAML sometimes provides additional options for more complex use cases that are not available through the UI.

threshold:
  type: above
  value:
    number: 30000

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 entity behind that target.

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

Behavior with multiple targets

When you target more than one entity (or select an area, floor, or label that contains several), the Trigger when option controls how the trigger responds:

• Each (any in YAML, default): the trigger fires every time any one of the targeted entities transitions. For example, if you monitor three motion sensors in the living room and someone walks past sensor 1, the automation fires. When they walk past sensor 2 a moment later, it fires again. Every individual event counts.
• First (first in YAML): the trigger fires only on the first transition in the targeted group, then waits until all targeted entities have reset before it fires again. For example, if you monitor the same three motion sensors, the automation fires when the first one picks up movement (someone entered the room). The other two firing afterward are ignored, so you get one notification per “someone walked in” event instead of three.
• All (last in YAML): the trigger fires only after the last targeted entity in the group has fired, meaning all of them are now in the expected state. For example, if you monitor the lights in the living room, bedroom, and hallway, the automation fires only once all three have turned off. This is useful for scenarios like “start the robot vacuum only after every light on the floor is off,” so you know the room is truly empty.

Good to know

• 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.
• Above and Below fire on the crossing moment only. Once the reading is above the threshold, the trigger does not fire again until the reading dips back below it and then crosses above again.
• In range (between) fires when the reading moves from outside the bounds into the bounds. Outside range (outside) fires when the reading moves from inside the bounds past either bound.
• Pair this trigger with Illuminance changed if you also want to react to smaller fluctuations between crossings.
• Use For at least to ignore brief light fluctuations, such as clouds passing or a person briefly shading an outdoor sensor.
• The trigger works with sensors that have the illuminance device class, and with number entities that use lux as the unit of measurement.

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.

Automation: turn on the desk lamp when the office gets dark

When the office illuminance crosses below 200 lx and stays there for at least one minute, turn on the desk lamp.

• Trigger: Illuminance crossed threshold
  • Target: Office illuminance sensor
  • Threshold type: Below 200 lx
  • For at least: 00:01:00
• Action: Turn on light
  • Target: light.desk_lamp

alias: "Desk lamp on when office gets dark"
triggers:
  - trigger: illuminance.crossed_threshold
    target:
      entity_id: sensor.office_illuminance
    options:
      threshold:
        type: below
        value:
          number: 200
      for: "00:01:00"
actions:
  - action: light.turn_on
    target:
      entity_id: light.desk_lamp

Automation: close the patio blinds in bright sun

Protect patio furniture by closing the blinds when the patio illuminance crosses above 30,000 lx for at least 5 minutes.

• Trigger: Illuminance crossed threshold
  • Target: Patio illuminance sensors
  • Threshold type: Above 30000 lx
  • For at least: 00:05:00
• Action: Close cover
  • Target: cover.patio_blinds

alias: "Close patio blinds in bright sun"
triggers:
  - trigger: illuminance.crossed_threshold
    target:
      area_id: patio
    options:
      threshold:
        type: above
        value:
          number: 30000
      for: "00:05:00"
actions:
  - action: cover.close_cover
    target:
      entity_id: cover.patio_blinds

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

These triggers work well alongside this one:

• Illuminance changed: Triggers after one or more illuminance values change.

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

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