Hello,
i search for a solution to dim my light when i start play netflix or amazon prime on my smart tv.
Can anyone help me?
You might want to help with specifying what television/integration you are using. But in the past with a Bravia Television I used an Automation of when state mediaplayer.tv is on enable scene, when off enable different scene, it worked well enough I havn’t changed it, except, I can’t find it in my interface anywhere but it still works 
But if you let us know more about your specific environment that would help in providing an useful answer.