Absolutely Confused, Can a vet explain?

Okay, so it's time to get a dehumidifier ASAP. My lights off temps have leveled out at 61 degrees Farenheit and SEVENTY SIX percent relative humidity. I have no clue how this is possible. Can someone explain to me how lights on my r/h is getting down to as low as 43%, and then the lights go off, temps drop about 9 degrees, and the relative humidity goes up as much as 33%? That's fucking nuts.

Because warm air holds more moisture than cool air. When your lights go off, temp drops, RH rises. If temps drop enough then RH will reach 100% and then dew forms. That is, there is more moisture than the air can hold and it drops out and forms dew.