What a poor analogy. The house is the cosmos. The architect is god. God is not a wall or a an interstellar gas cloud. The architect can make his presence unambiguously known to anyone living in the house. God cannot (for obvious reasons).
And this light is...? The fact that we have a much more detailed understanding of nature than either of these fine gentlemen somehow limits our real understanding? My oh my. What a ringing endorsement for ignorance.
The analogy means exactly what it implies. One could only call it a poor analogy if it did not, in fact, have a solid metaphoric appropriation to what the author purports to imply. Indeed, an architect
can make his presence clearly known to anyone living in the house. As a Christian, Lewis will argue that God did, in fact, make his presence known in the cosmos at a particular historical juncture, in the person of Christ by the hypostasis of incarnation. If someone does not, on dogmatic principle, believe God could exist, of course the analogy would appear poor, since they subject the "God side" of the analogy to the same method of verification as the "architect side" of the analogy. They cannot accept that God is "like" the architect because an architect exists whereas God does not. That seems to simply ignore the point the analogy makes, rather than manifesting merely a poor analogy. Such a reduction in meaning makes not just this analogy, but all analogies poor: we use analogies to illustrate something unknown
by means of something already known. In the aforementioned quote, then, Lewis addresses the very issue you raise: he is saying that such a complaint that God cannot be verified by means of the scientific method is nonsense. He does not, however, say that there is no other way to find God out. But, as I said before, those methods most moderns will not accept, because they're not taught not to, and they take the word of science on authority rather than reason.
The light I refer to is Truth, Meaning, Significance. We do, indeed, have a much more detailed understanding of nature than did the ancients and the medievals. However, because of the slant toward specialization, many people believe that their particular little quadrant of knowledge can explain the entirety of reality; e.g., some think everything can be explained by means of cognitive science, or physics, or biology, or economics. So I am not advocating "ignorance," but escape from ignorance into a more transcendental perspective: this perspective is not the
abandonment of knowledge but the
synthesis of all knowledge. If a Plato or a Shakespeare lived today, they could see how all of the knowledge we do have points to truths beyond solely empirical events, by--who knew?--the subtle power of inference. They would see what they saw even more clearly, because they have more detail.