You're welcome. Lorna and Michael (the wonderful people who are behind f.lux) have taught me during my time on this forum that the brightness level is almost as important as how much blue light is in the light source - at least as it pertains to how 'alerting' it is for the body. Of course, it's also easier on the eyes when you've been awake all day and are getting tired. We get very sensitive to light after being awake for ~14 hours.
You might also be able to reduce the amount of blue light your monitor emits by adjusting its colors using its built-in menu system.