Śatapatha Brāhmaṇa ("of a hundred paths") 8.3.2.2

8.3.2.2

yadveva viśvajyotiṣamupadadhāti | prajā vai viśvajyotiḥ prajā hyeva viśvaṃ jyotiḥ prajananamevaitadupadadhāti tāmanantarhitāṃ diśyābhyā upadadhāti dikṣu tatprajā dadhāti tasmātsarvāsu dikṣu prajāḥ

And, again, as to why he lays down the Visvagyotis,--the Visvagyotis, doubtless, is offspring (or creatures), for offspring indeed is all the light: he thus lays generative power (into that world). He places it so as not to be separated from the regional ones: he thus places creatures in the regions, and hence there are creatures in all the regions.