Differences between 'soft' and 'light' charcoal pencils
The characteristics between soft charcoal pencil and light charcoal pencil are different. Soft charcoal pencil is darker than medium and hard charcoal pencil, it is a black color.
It's easy to crush, and the first time I used it, it became very short in one day. 'Light' charcoal have two meanings:

Light can mean hard, as 'light, medium, dark' corresponds with 'hard, medium, soft':
Light = Hard charcoal pencil.
Dark = Soft charcoal pencil.
Light can refer to the white charcoal pencil in some brands, used to draw lighter areas.

Ignore the second meaning when the brand states &quot;Light, Medium, Dark&quot; - it means the same as HB to 4B, giving good results from light to dark.
When the brand states &quot;Soft, Medium, Hard&quot; (as for example Han Zi, a Chinese brand, does), there is hardly a difference between the light to dark results.
But soft charcoal pencils give nice results in drawing, too. Using my soft charcoal pencil results in the center of it being darker than the edges, giving a Photoshop-like blur brush effect.