why is external display brighter and better when in clamshell mode?

[madeirabhoy]

I have an M2 MBA connected to an external monitor. when the MacBook is open and so both screens are on, the external display is a little washed out. I close the lid, and immediately it's more vibrant and colorful. why does this happen?

 

[DJ Rob]

Not sure if this is what you mean by washed out, but when True Tone is enabled, it gets applied to the external screen when the lid is opened. Essentially, the monitor goes from cool to warm color temperature. Try toggling that setting and see if it helps.

 

[SmOgER]

When you close the lid all the display settings like resolution scaling are applied exclusively for your external display without considering the internal display. If you want for it to stay crisp in extended display mode and use both screens simultaneously, install BetterDisplay app to have it interpreted as retina HiDPI regardless of your scaling (not just native tiny text or half res huge text) - best decision I have made when it comes to connecting any external screen.

EDIT: If you are using mirroring mode do not do that - it becomes a mess since you can't have the same image looking perfect on 2 different screens, especially if they have different aspect ratio.