HankScorpio, a single 50ppd for an 8k? Must either be a fresh air room, or have tiny little plants w/o much foliage.
Hey Joe, what are your night time temps?
If you warm the room a bit at night your RH will drop considerably. Warm air can hold more moisture than cold air hence the drop in RELATIVE Humidity. Your AC is dehumidifing during lights on so just raise the temp at night a little bit at a time until you get to an acceptable RH.