In my smart home I use multiple IKEA Tradfri lights in combination with a Conbee Zigbee hub and Home Assistant. Recently I encountered a problem when trying to set both the brightness and the color temperature in a Home Assistant service call (light.turn_on). Apparently, the Tradfri bulbs only respond to one of these values at a time. This is unfortunate as changing the temperature and brightness is usually linked. For example, setting the lights to a dimmed warm setting at night or bright white in the morning. Luckily, there is a workaround to be able to set both simultaneously (sort of at least).

The solution to setting brightness and color temp on Tradfri lights is to split the single service call in to two and let those blend. In my setup, I first set the brightness of the lights with a small transition and use a second call to change the color temperature with a longer transition. I have tested multiple setups and this method results in the smoothest transition. In essence my workaround performs three steps:

  1. Turn on the light with the target brightness.
  2. Delay for a second to make sure that the previous call has finished.
  3. Set the color temperature of the light with a short transition (5 seconds).

By putting these steps in to a script it can act as a drop-in replacement of a normal light call. If one of the settings was already set earlier, for example the brightness did not change, the transition is even smoother.

I have created two versions of this workaround, one for Home Assistant (YAML) and one for Node-RED, to help others that encounter this problem. It is not the most elegant solution but in practice it works pretty good!

Home Assistant script

To use the workaround in Home Assistant (yaml) add the following snippet to scripts.yaml:

    # Check whether the light is off (optional)
    - condition: template
      value_template: "{{ is_state(entity, 'off') }}"
    - delay: '00:00:01'
    # Set the brightness of the lights.
    - service: light.turn_on
        entity_id: "{{ entity }}"
        brightness_pct: "{{ brightness_pct }}"
        transition: 1
    - delay: '00:00:01'
    # Set the color temperature.
    - service: light.turn_on
        entity_id: "{{ entity }}"
        color_temp: "{{ color_temp }}"
        transition: 5

This block of code adds a new script turn_on_ikea_light that can be called inside automations. entity, brightness_pct and color_temp are variables that can be set when calling the script. An example is the following automation where a light is turned on when a motion sensor registers movement:

# Example automation using the script
  - alias: Turn on lights on movement
      - platform: state
        entity_id: sensor.motion_sensor
        to: 'on'
      service: script.turn_on_ikea_light
        # Variables that are passed on to the script:
        entity: light.some_light_entity
        brightness_pct: 80
        color_temp: 350

Node-RED script

I’ve recently switched most of my automations to Node-RED so also rewrote my workaround. In Node-RED we need two service calls to HA (one for brightness and one for color temp). In the most simple case this can be done with two “call service” nodes and a delay node. To be able to reuse the flow this can be created as a subflow:

Subflow to set brightness and color temperature on Ikea lights

The subflow shown above expects a JSON message as the msg.payload. The payload is then split in to the two service calls. For example, to set the temperature of a light to 150 and the brightness to 100%, one could send the following payload:

    "entity_id": "light.some_light_entity",
    "color_temp": 150,

The values can be hard coded in a change-node or can be dynamically set (for example based on the time of day).

Complete flow in Node-RED. Replace the inject node with something useful, e.g. a motion event.

The nodes of the subflow can be imported using the following snippet:

[{"id":"13593ff8.a6556","type":"api-call-service","z":"2dc416a2.d3b6fa","name":"Turn on lights","server":"161bb087.35566f","service_domain":"light","service":"turn_on","data":"{\"entity_id\":\"light.some_entity\",\"transition\":1}","render_data":false,"mergecontext":"","output_location":"payload","output_location_type":"msg","x":700,"y":480,"wires":[[]]},{"id":"7167f74f.dd6528","type":"api-call-service","z":"2dc416a2.d3b6fa","name":"Set color temp","server":"161bb087.35566f","service_domain":"light","service":"turn_on","data":"{\"transition\":5}","render_data":false,"mergecontext":"","output_location":"payload","output_location_type":"msg","x":840,"y":420,"wires":[[]]},{"id":"96a91d65.7a1a4","type":"delay","z":"2dc416a2.d3b6fa","name":"","pauseType":"delay","timeout":"1","timeoutUnits":"seconds","rate":"1","nbRateUnits":"1","rateUnits":"second","randomFirst":"1","randomLast":"5","randomUnits":"seconds","drop":false,"x":680,"y":420,"wires":[["7167f74f.dd6528"]]},{"id":"b76ccf31.5d0c","type":"function","z":"2dc416a2.d3b6fa","name":"Split payload","func":"br = {\n    payload: {\n        data: {\n            entity_id: msg.payload.entity_id,\n            brightness_pct: msg.payload.brightness_pct\n        }\n    }\n}\n\nwarmth = {\n    payload: {\n        data: {\n            entity_id: msg.payload.entity_id,\n            color_temp: msg.payload.color_temp\n        }\n    }\n}\n\nreturn [warmth, br]\n","outputs":2,"noerr":0,"x":490,"y":440,"wires":[["96a91d65.7a1a4"],["13593ff8.a6556"]]},{"id":"161bb087.35566f","type":"server","z":"","name":"Home Assistant"}]