One data point about hydroponics. The 4 tomato plants in the photo were started late February in 3X3 rock wool blocks.
On March 6th the 2 on the right were transferred to a hydroponics setup and the 2 on the left were put into an enclosed frame indoors. Both were under LED lights. Humidity around the hydroponics is about 40% and temperatures range from 60 to 70. Humidity in the enclosed frame is close to 100% and temperatures range from 60 to 70.
The 2 on the left were actually starting to fail so I potted them up today. The 2 on the right were getting to large and starting to spread and the rightmost one appeared to be wilting so I potted them up today.
They are now in the daily shuffle of plants out into the sun on warm days.
100% humidity = 0 transpiration is what I am seeing. without the ability to move H2O, O2, and CO2 through the plant and leaves effectively, due to 100% humidity, the photosynthetic reaction stalls out. This is also a good demonstration of why it is important to keep the air moving in your grow set up. Moving air, with less than 100% humidity 😉, helps to drive transpiration, which in turn drives photosynthesis which leads to more plant growth.