How do aisle lights show the direction to exits?
The Floor Proximity Emergency Escape Path marking requirements (for transport category aircraft certified under FAR Part 25) have to meet the specific requirements as noted in the regulatory excerpt below.  There are different configurations that may be used to satisfy the regulations.
FAR §25.812   Emergency lighting. (excerpt):

(...) In the dark of the night, the floor proximity emergency escape path marking must enable each passenger to—
(1) After leaving the passenger seat, visually identify the emergency escape path along the cabin aisle floor to the first exits or pair of exits forward and aft of the seat; and
(2) Readily identify each exit from the emergency escape path by reference only to markings and visual features not more than 4 feet above the cabin floor.

Here is a sample from the Flight Safety Foundation showing an example of floor proximity escape path markings.

(Source)
Also, here is a link to a Flight Safety Foundation article regarding floor proximity lighting.