Factors affecting amount of water vapour produced by lower and upper epidermis of leaves?

Question

An experiment is carried out to determine the transpiration index of upper and lower epidermis of leaves both in light and dark. What could cause the transpiration index of lower epidermis to be higher than those of upper epidermis besides the number of stomata? And how does the light/ dark condition affect the amount of water vapor produced by plants?

Answer 1

cuticle thickness

Answer 2

answer for the first question has been answered.but for the light and dark one, it is due to different rates of photosynthesis and underlying metabolic activity which results in differential stomatal openings.The light effect is also regulated by several signal transduction mechanisms depending on blue as well as red light.