Response of plant transpiration to changes in light.
 

I am examining the affect of light on transpiration, comparing the
plant's transpiration rate in the dark to that in the light. At the
points of transition from light to dark, the plant's transpiration
rate decreases almost immediately, however, when the light was turned
on after the plant had acclimated to the dark over 70 minutes, it took
nearly seven minutes for the plant to show any change in its rate of
transpiration.

The question is "why the difference in the plant's response time?"
This could be similar to the eye's reaction to changes in light, as
the pupil closes faster than it opens, because bright lights are
damaging whereas darkness is not. Any ideas or observations?

Thanks,
Amy Caes