Light detected

The Light detected trigger fires when one or more light sensors start detecting light.

Use it to automate actions when a dark area becomes lit, like sending a notification when a closet light is accidentally left on, or turning off a night light at dawn when an outdoor sensor first picks up daylight.

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 this trigger 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. From the search box, search for and select Light detected.
5. Select Add target (see Targets) and pick the light sensor that you want to watch. You can also select an area, a floor, a device, or a label.
6. Under Trigger when (see Behavior), pick Each, First, or All to control how the trigger behaves when multiple sensors are targeted.
7. Under For at least, you can set how long the sensor must keep detecting light before the trigger fires. Leave it at zero to fire immediately.
8. 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, refer to this trigger as illuminance.detected. A basic example looks like this:

trigger: illuminance.detected
target:
  entity_id: binary_sensor.closet_light_sensor
options:
  for:
    minutes: 5

This fires 5 minutes after the closet light sensor starts detecting light.

Options in YAML

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

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

• This trigger works with binary sensors that have the light device class. The sensor’s threshold for what counts as “light detected” is set on the device itself.
• For numeric illuminance readings (in lux), use Illuminance changed or Illuminance crossed threshold instead.
• Combine For at least with a small duration to avoid false triggers from brief light flickers, such as headlights passing a window.

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: notify when the closet light is left on

When the closet light sensor detects light for more than 10 minutes, send a notification so a light left on by mistake doesn’t go unnoticed.

• Trigger: Light detected
  • Target: Closet light sensor
  • For at least: 00:10:00
• Action: Send a notification message
  • Target: My Device (notify.my_device)

alias: "Notify if closet light is left on"
triggers:
  - trigger: illuminance.detected
    target:
      entity_id: binary_sensor.closet_light_sensor
    options:
      for: "00:10:00"
actions:
  - action: notify.send_message
    target:
      entity_id: notify.my_device
    data:
      message: "The closet light has been on for over 10 minutes."

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:

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

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

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