The tube brightness can be changed in software by adjusting how high the boost converter voltage is set which is changed by adjusting the boost PWM duty cycle. Changing the brightness will keep the clock readable in different settings. This setting is stored permanently in EEPROM.
Please note: VFD tube life seemt to be related to driving voltage. So we suggest keeping the brightness lower if you can, as it will keep the tube lasting longer!
Press the MENU button until Set brit is displayed.
Now press the SET button to change the brightness.
The current setting is shown.