Equivocation Fallacy?

Expanding on what Rationalissimo wrote, yes, this is Equivocation . The reason is that light "existing" is very different from good existing. The former refers to a physical existence (photons) and the latter refers to a conceptual existence. Futher, it is an assertion, nothing more. We can no more demonstrate that good is the absence of evil than we can evil is the absence of good.

It's not a fallacy, it's an assertion with an illustration for an analogy.

This is Reification 

Cold and Darkness don't exist as quanta (like heat and light do), but they are certainly qualia. Qualia are sensations, felt by living things, and can be ascribed names. Thus, they exist. 

I started off writing this:

I don't think it is, it seems to be fairly reasonable at a cursory glance. However we need to delve deeper to see if there's any substance to the argument.

First we need to examine whether good is a thing which can be present. In most contexts good is an evaluation of something. If the claim is that good is a force of some kind, then I'd have to see some sort of evidence to substantiate such a claim.

Second we need to look at whether evil is simply the absence of good.

However it was at this point that I noticed that the quote starts off with "moral evil"* and then switches to "evil". Furthermore it states that "good exists" which clearly refers to a force rather than an evaluation, so absolutely, this is an example of equivocation.

I would say that it may also an example of begging the question as the argument assumes the premise that good exists rather than demonstrate it. 

And of course I'd say that it's a weak analogy as it's being compared to things which can be detected and measured rather than just asserted. 

* A quick search returns:

Moral evil is any morally negative event caused by the intentional action or inaction of an agent, such as a person. An example of a moral evil might be murder, or any other evil event for which someone can be held responsible or culpable.

This clearly isn't the same as a force or entity of good.

Also to add in my original reply I was going to touch on a lack of good not being the same as evil, as you can lack any good behaviour without causing harm to others. In that sense the description of evil which we use to describe actions or a person is not the same as a lack of good at all.

Along with all the other fallacies suggested here, I would also add the Faulty Comparison Fallacy as it is falsely comparing qualia with quanta. 

I would say this is more poetry than logic. 

I don't see equivocation, but rather an argument from analogy.Weak Analogy