Dharmakāya is emptiness, definitely not a source. The five lights are originally pure, which means they're primordially unborn and free from extremes.
Duffster, regarding your question; 'spirituality' is a fairly broad term and could represent various systems, religions and traditions, all having different ideas of a source. In Vedanta for example, the source of phenomena is called Brahman. Dzogchen however doesn't posit a 'source' of phenomena per se... It's said that the way we usually perceive phenomena is incorrect, and that is the reason we suffer. So the system of dzogchen is predicated on recognizing the true condition (or nature) of phenomena. The dharmakāya signifies the empty nature of phenomena, which means that in truth phenomena are non-arisen and do not accord with any of the four possible extremes, which are: existence, non-existence, both and neither. When we realize that phenomena are truly unborn and non-arisen then that is called dharmakāya. That realization liberates us from our ignorant misconceptions that phenomena can exist, not exist, etc. which means we are free from the causes and conditions which sustain delusion and suffering.
Homage to the Dzogchen Masters!
"In reply to Vajrasattva's question as to the nature of the dimension of reality (dharmakaya) and the light of wisdom, the Teacher states that the dimension of reality is the lack of concreteness of the universe, and the inconceivable light of wisdom is not different from that and is as vast as that. This light is beyond comparison with the luster of the buddhas or of the sun and moon: it is the infinite radiance of the wisdom of one's self."
From the The Marvelous Primordial State
Not to worry. The bottom line is that whatever
your understanding is, this present understanding is also empty of any concrete self nature (dharmakaya) and this understanding (whatever it is), as it manifests in the continuum of your awareness, is the infinite radiance of the wisdom of one's self.
Relaxing into this radiant wisdom of whatever manifests, the question, (and all questions) of whether the dharmakaya is the source, is resolved (beyond words or concepts) in itself: your own radiant wisdom. Beyond this there is no answer to the question and any answer (whatever manifests) is ok, informed by that radiance.
Now you've got it!
In the case that there still is any question, take the direct introduction, pointing out instruction, from a qualified Dzogchen Master and perhaps this experience will clarify the meaning.