When will chloroplasts be aligned with their flat surfaces parallel to the walls in mesophyll cells? when will they be perpendicular to the incident light?

Flat surface parallel to mesophyll walls  position

Chloroplast assumed this position  in condition of low  light intensities or optimum light intensities   for the reception of maximum amount of incident light. necessary for photosynthesis

Perpendicular to the incident light position.

During condition of extreme high light intensities chloroplast  aligned in this position to avoid the loss of electrons from the chlorophyll from absorption of photons; (PHOTOXODATION.)  

Basically photooxdation is a wasteful process which destroys the plants.

Explanation:

igneous rocks which formed by the crystallization of magma at the surface of the earth called extrusive rocks. they are characterized by fine-grained textures because the rapid cooling at or near the surface did not provide enough time for large crystals to grow.