Prodigit, that is clearly a case where an exchange is in order. Maybe you could post a picture of it with light at 24 in a dark room. If it is as you describe, there is a fault with your light guide.
About your theory about light canceling each other out: yes it is possible. It is even easier to go by this: reflecting light on all wavelengths the same is a non-trivial matter. And since the light guide cannot possibly be a simple construct of reflection, you also deal with refraction. This by itself can cause grief. Why do you think a good SLR lens is worth thousands of dollars if even sharpness and no color-fringing is needed without loss of too much light on the way (as in lower f-stop numbers).
I suggest you post that picture, let us look at it, and if it is aweful, you should call Amazon and complain about a faulty unit.
Update: oh, just in case you have not seen it, but
post #83 shows my 2 PW - this is what they can look like. No they are not perfect, but looks a lot better than what you describe.