Transpiration speeds up when a plant is carried into brighter light. Which change in the leaf is the main reason for that?

Explanation

Bright light causes the guard cells to open the stoma each pair encloses, and an open pore gives water vapour a much wider escape route, so more of it gets out. Light does bring warmth with it, but the opening of the pores is the change that actually lets the vapour through, and a plant kept equally warm in the dark loses far less water than the same plant in the light.