Question

What are the connecting substances between light and dark reaction

Answer 1

The light phase and dark phase describe the photosynthetic reactions which take place in the chloroplasts of plant.

The light phase requires sunlight which is used to split water molecules. The products of this reaction are oxygen and energised hydrogen atoms which are attached to energy carriers (specifically ATP and NADH).
NADPH and ATP which are produced in the light reaction are then used in the dark reaction, in combination with carbon dioxide, for the synthesis of glucose.