TypeError: <lambda>() takes no arguments (1 given)
You should consult Tkinter documentation:
Scale widget
command- A procedure to be called every time the slider is moved. This procedure will be passed one argument, the new scale value. If the slider is moved rapidly, you may not get a callback for every possible position, but you'll certainly get a callback when it settles.Button widget
command- Function or method to be called when the button is clicked.
Change your lambda to
command=lambda new_scale_val: scale_changed('LED')