Typically the distance between nodes (where the leaves emerge from the stems) increases when light levels are too low. Increasing the photoperiod may help but I find it seems to be more related to light intensity.
Yeah, plants "stretch" toward the light if it's not strong enough, resulting in longer internodes (section between nodes - leaves), rather than compact growth. You will notice shorter internode sections that are closer to the top since it is obtaining more light.
Red spectrum of light also plays a factor in internode spacing. More red spectrum light will have plants with shorter internodes.