Screen brightness during demonstration

[virvira]

My screen works fine without demonstration https://monosnap.com/file/AwjzhFEibmR65OqJM5NYrAHx1qiQ6M 
But during demonstration my colleagues see the screen like a https://monosnap.com/file/hZjgstXPCBUY0ltByJ1bsdqDHTPGfG 

What could be the problem?