The brahmajyoti is actually the effulgence of the Supreme Personality of Godhead. As stated in Brahma-saṁhitā (5.40):

yasya prabhā prabhavato jagad-aṇḍa-koṭi-
 koṭiṣv aśeṣa-vasudhādi-vibhūti-bhinnam
tad brahma niṣkalam anantam aśeṣa-bhūtaṁ
 govindam ādi-puruṣaṁ tam ahaṁ bhajāmi

“I worship Govinda, the primeval Lord, who is endowed with great power. The glowing effulgence of His transcendental form is the impersonal Brahman, which is absolute, complete and unlimited and which displays the varieties of countless planets, with their different opulences, in millions and millions of universes.” Although the impersonal feature of the Absolute is an expansion of the rays of the Supreme Personality of Godhead, He does not need to take care of the impersonalists who enter the brahmajyoti. Kṛṣṇa says in Bhagavad-gītā (9.4), mayā tatam idaṁ sarvaṁ jagad avyakta-mūrtinā: “In My impersonal feature I pervade this entire universe.” Thus the avyakta-mūrti, the impersonal feature, is certainly an expansion of Kṛṣṇa’s energy. Māyāvādīs, who prefer to merge into this Brahman effulgence, worship Lord Śiva. The mantras referred to in text 29 are called mukhāni pañcopaniṣadas taveśa. Māyāvādīs take all these mantras seriously in worshiping Lord Śiva. These mantras are as follows: (1) tat puruṣāya vidmahe śāntyai, (2) mahā-devāya dhīmahi vidyāyai, (3) tan no rudraḥ pratiṣṭhāyai, (4) pracodayāt dhṛtyai, (5) aghorebhyas tamā … , (6) atha ghorebhyo mohā … , (7) aghorebhyo rakṣā … , (8) aghoratarebhyo nidrā … , (9) sarvebhyaḥ sarva-vyādhyai, (10) sarva-sarvebhyo mṛtyave, (11) namas te ’stu kṣudhā … , (12) rudra-rūpebhyas tṛṣṇā … , (13) vāmadevāya rajā … , (14) jyeṣṭhāya svāhā … , (15) śreṣṭhāya ratyai, (16) rudrāya kalyāṇyai, (17) kālāya kāmā … , (18) kala-vikaraṇāya sandhinyai, (19) bala-vikaraṇāya kriyā … , (20) balāya vṛddhyai, (21) balacchāyā … , (22) pramathanāya dhātryai, (23) sarva-bhūta-damanāya bhrāmaṇyai, (24) manaḥ-śoṣiṇyai, (25) unmanāya jvarā … , (26) sadyojātaṁ prapadyāmi siddhyai, (27) sadyojātāya vai namaḥ ṛddhyai, (28) bhave dityai, (29) abhave lakṣmyai, (30) nātibhave medhā … , (31) bhajasva māṁ kāntyai, (32) bhava svadhā … , (33) udbhavāya prabhā … , (34) īśānaḥ sarva-vidyānāṁ śaśinyai, (35) īśvaraḥ sarva-bhūtānām abhaya-dā … , (36) brahmādhipatir brahmaṇodhipatir brahman brahmeṣṭa-dā … , (37) śivo me astu marīcyai, (38) sadāśivaḥ jvālinyai.

The impersonal Brahman is unknown even to the other directors of the material creation, including Lord Brahmā, Lord Indra and even Lord Viṣṇu. This does not mean, however, that Lord Viṣṇu is not omniscient. Lord Viṣṇu is omniscient, but He does not need to understand what is going on in His all-pervading expansion. Therefore in Bhagavad-gītā the Lord says that although everything is an expansion of Him (mayā tatam idaṁ sarvam), He does not need to take care of everything (na cāhaṁ teṣv avasthitaḥ), since there are various directors like Lord Brahmā, Lord Śiva and Indra.