Here is an example using a change node and JSONata expression
first it matches the numbers
then i loops though the matches and converts the strings to numbers. finally it takes the numbers and creates the object.
[{"id":"d72d6c96.dacd","type":"inject","z":"7f59364f045fd16d","name":"","props":[{"p":"payload"},{"p":"topic","vt":"str"}],"repeat":"","crontab":"","once":false,"onceDelay":0.1,"topic":"","payload":"temp(46,3840)","payloadType":"str","x":230,"y":580,"wires":[["a7cfb606.aecfc"]]},{"id":"a7cfb606.aecfc","type":"change","z":"7f59364f045fd16d","name":"","rules":[{"t":"set","p":"payload","pt":"msg","to":"[[$match($$.payload, /\\d+/).match.$number($)]].{\"brightness\":$[0],\"color_temp\":$[1]}","tot":"jsonata"}],"action":"","property":"","from":"","to":"","reg":false,"x":460,"y":580,"wires":[["a966cb14.c37eb"]]},{"id":"a966cb14.c37eb","type":"debug","z":"7f59364f045fd16d","name":"","active":true,"tosidebar":true,"console":false,"tostatus":false,"complete":"false","statusVal":"","statusType":"auto","x":640,"y":600,"wires":[]}]