Baal HaSulam, The Teaching of the Ten Sefirot, Part 2, “Inner Reflection,” Item 63: We refer to the Hamshacha (attraction of the Light) by the Ne’etzal (the created being) as Hitpashtut (expansion) of Ohr Elyon (the upper Light).
At the very moment when the created being yearns to receive from the upper Light, he immediately sucks the Light. It is like one who lights a candle from another and the first is not lessened by it. By the same manner, when the created being extends the upper Light to itself, the upper Light is not lessened in any way because of that part that the created being extended.
Also, it is not affected or impressed in any way by the attraction of the Light by the created being. However, in order to simplify matters, we refer to this as the expansion of the upper Light.
Remember this in every place for we always speak of the expansion of the upper Light and mean the attraction of the Light by the created being by his Hishtokekut (yearning) alone.
There cannot be any movement or change in the Light itself—all changes occur in the desire of the created being. We don’t emphasize it every time and simply say that the Light descends from Above, however, the Light cannot come anywhere.
It means that we reveal this Light by the order of the vessels (desires) that descend from Above downward. They are like a chain of candles lit one after the other. We say about it: The Light comes. It means that a vessel appears and it reveals the Light, reacts to it.
The Light existed before and it exists right now; it does not change! However, each time we have new desires that reveal this Light, and hence we say it as if the Light changes. But there are no changes in the Light; they only occur in the vessel. The Light becomes revealed according to the vessel’s desire to do so.
Prior to that the Light existed, but it was concealed. Now it is revealed. However, it does not affect the Light in any way because the vessel decides in which form the Light will become revealed.
From the 3rd part of the Daily Kabbalah Lesson 9/4/2011, TES