A humidity percentage cannot describe the grow-room environment on its own. Temperature changes the relationship between moisture in the air and the demand for water from the plant.
Vapour pressure deficit, or VPD, helps describe that demand. Low and high values create different conditions for water loss. Young cuttings and established plants also have different needs.
Use temperature and humidity readings together, measured where the crop is growing. Where you calculate leaf-to-air VPD, the leaf-temperature assumption matters. A chart is useful context, but it is not a complete diagnosis of plant water status.
Next step: review the pattern across lights-on and lights-off. Check the canopy, not only the controller mounted elsewhere in the room. Interpret the environment alongside irrigation and plant response.
Reviewed 8 October 2026