Vapour pressure deficit is set by leaf temperature, not air temperature. Move the sliders and watch the target window move with the growth stage.
Leaf VPD
0.85kPa
Inside the target bandTarget window0.8–1.2 kPa
Leaf temperature22.0 °C
Air VPD1.19 kPa
Dew point15.8 °C
Absolute humidity13.1 g/m³
RH for mid-band55 %
0.85 kPa is inside the 0.8–1.2 kPa window for this stage. Transpiration and nutrient transport are both where you want them.
Air temperature24.0 °C
Relative humidity60 %
Leaf temperature offset-2.0 K
Under LEDs a transpiring leaf usually sits 1–3 K below air. Under HPS or CMH the extra infrared can push it above air, so the slider also goes positive.
Growth stage
Matrix colours follow the selected stage: the band shifts when you change it.
Scroll the matrix sideways to see the whole humidity range
How this is computed: saturation vapour pressure from the Buck (1996) equation over liquid water; actual vapour pressure as es(T_air) × RH; leaf VPD as es(T_leaf) − e_actual, which is the gradient the stomata actually see. Dew point uses the inverse Magnus form, absolute humidity the ideal-gas relation with Rv = 461.5 J/(kg·K). Target bands are the ranges in common commercial use — treat them as a starting point, not a specification, because cultivar, light intensity and root-zone conditions all move the optimum.