This reminds me of the last Panasonic we purchased. It was a stainless 32L one and when we opened the door, no light came on. It only lit when cooking. We thought this was a fault but apparently it was a feature of this model. No other Panasonic or microwave we have had did this. We now have Samsung and the light inside when cooking is so dim that you can’t see it cooking without turning off all the lighting in the room. Both cooked fine though and reliable.
I like no light when the door is open because that's how you let it dry out and leaving an incandescent light running while its open is just wasteful. I dont need light for that because the door is open. Perhaps if I was midnight snack nuking it would be helpful but really they should give you a button for it. Sure would be more use than the many food names they make buttons for that never get used.