MAX7219 resistor value
From the MAX7219 datasheet page 8:


  The MAX7219/MAX7221 allow display brightness to be
  controlled with an external resistor (RSET) connected
  between V+ and ISET. The peak current sourced from
  the segment drivers is nominally 100 times the current
  entering ISET. This resistor can either be fixed or variable
  to allow brightness adjustment from the front
  panel. Its minimum value should be 9.53kΩ, which typically
  sets the segment current at 40mA. Display brightness
  can also be controlled digitally by using the
  intensity register.


Set to suit your display.