Configurable transition state publish interval for lights

[nohat]

Component name

light

Link to component documentation on our website

https://esphome.io/components/light/

Describe the enhancement

When using ESPHome lights with transitions (e.g. transition_length or flashes), the remote state that Home Assistant (or other frontends) sees usually jumps directly to the final state at the start of the transition.

This is efficient, but it means frontends don't know about the intermediate states along the fade. As a result:

• Front-end UI transitions "jump" to the end value and users have no feedback in the UI as to the actual state of the light for longer transitions.
• It's difficult to build smooth, synchronized animations in dashboards or wall controllers that reflect the real transition of the light.

I would like a configurable option on lights that causes state updates to be published periodically during transitions, so frontends can animate along the actual fade path.

Use cases

• Smooth, visually accurate light fades in Home Assistant dashboards, tablet UIs, and physical controllers.
• When a user changes brightness or color with a transition, the UI should track the fade in near-real-time instead of snapping to the final state.

Alternatives I've tried:

• Using rapid-fire light.turn_on commands with small step transitions to approximate a smooth fade. This:
  • Increases complexity in automations.
  • Generates a lot of traffic.
  • Still doesn't always match the device's actual timing.
• Relying on front-end animations that assume a fixed duration, which can easily drift from the actual transition behavior on the device.

Anything else?

Proposed solution

Add a per-light configuration option, e.g.:

light:
  - platform: monochromatic
    id: my_light
    output: ...
    default_transition_length: 1s
    transition_state_publish_interval: 200ms

Semantics:

• transition_state_publish_interval: 0s (default)
  • Preserves current behavior:
    • Initial publish reports the final/target state.
    • No additional publishes occur due to this feature.
• transition_state_publish_interval > 0
  • Initial publish for a transition reports the starting state.
  • While a transition or flash is active, ESPHome periodically:
    • Copies current_values to remote_values.
    • Calls publish_state() at the configured interval.
  • When the transformer finishes:
    • A final state is published.
    • If persistence is enabled, the final state is saved once.

Scope:

• Applies to all transformer-based transitions (including flashes).
• Does not change behavior of effects that explicitly disable publishing via call.set_publish(false).

Considerations / trade-offs

• The feature is entirely opt-in; default 0s keeps the existing behavior and avoids extra traffic.
• Small intervals (e.g. 10ms) can significantly increase publish frequency, which may:
  • Increase network traffic (MQTT/API).
  • Increase CPU usage on both ESP and frontend.
• Recommended to document reasonable ranges (e.g. 100–500ms) and trade-offs.

How this relates to other requests

This is a foundational feature for smoother light control and pairs well with:

• esphome/feature-requests#3207 – Support smooth dimming of lights

The transition state publish interval makes it possible for frontends to observe the actual transition path, which in turn enables smoother dimming UX and future dynamic control features.

[github-actions[bot]]

🏷️ I've automatically added the component: light label to help categorize this feature request.