In both cases, maxlight is the maximum light a lighting node is placed to. If you, for example, pass 0 to the chatcommand, then the lighting nodes are only placed where the light is zero.
The lighting nodes which are placed are from the currently wielded itemstack, or the stack right to it.
light_cave [maxlight] automatically lights up a whole dark region where the player looks at.
auto_light_placing [maxlight] enables a function for the player which constantly tests where the player looks at; if it is dark at a pointed position, the function makes the player automatically place the light node there.
If you want to see light values at specific positions, try the superpick mod.
Download: zip, tar.gz
github: cave_lighting
If you got ideas or found bugs, please tell them to me.
How to install a mod?