Vaishnava Mantra of the week...

ॐ बृहद्भानवे नमः 

OM bR^ihadbhAnave namaH

This is The Name 333 of "Shree Vishnu-SahasraNam". While preparing this post I have checked up the edition of "Shree Vishnu-Sahasranam" by SADAGOPAN.ORG (link to 2nd Volume) and Sadagopan's edition refers to
the Mantra 2.2.10 from "Shree Mundaka-Upanishad". 

So if you are interested in Upanishadic Siddhanta behind "OM bR^ihadbhAnave namaH" Mantra of Bhagavan Shree Narayana, then "Shree Mundaka-Upanishad", 2.2.10:

Translation (from this edition by B.D.Basu): "The Sun does not shine there in His Presence nor The Moon and the stars (for The Light of Bhagavan Shree Narayana is greater than theirs and they appear as if dark in Bhagavan Shree Narayana's Effulgence - like the candle-light in The Sun). 

Nor do these lightings and much less this fire shines there. When Bhagavan Shree Vishnu shines, everything shines after Him; by His Light all this become manifest"

And 2 classic Tikas are the following:

Tika by OM VishnuPad Parashara Bhatta MahAcharya (Shree Ramanuja-Sampradaya): "The Illuminating Rays of Bhagavan Shree Vishnu are Nitya (Eternal) and the Name BrihadBhanu shows that Bhagavan Shree Vishnu is The Greatest Sun indeed."

Tika by ShankarAcharya: "Bhagavan Shree Narayana is The Possessor of Great Rays. Any illuminations (like the Sun or The Moon) derive their light from Bhagavan Shree Vishnu only. And all the Universe is actually illuminated by Bhagavan Shree Vishnu".