After looking at the dim light code in question and comparing it to the default lights, I noticed only one difference.
radius = 2;
brightness = 2;
This is the Dim light's data. It produced no visible light in-game.
It appears the problem may be related to a potential lower bound for light emitted:
I changed the value to half of the default light's radius and brightness, and got a noticeable result.
I divided these numbers by two once again, and got a smaller light, but a light none the less.
Badspot should explain this result to me, or someone with similar knowledge.