In my humble opinion:
Looking at this as a map of human awareness levels or possible zones, each sphere can represent a direction for an altered state, and each altered state or combination of them, supplies different skills. Being at the top, Kether/Keter represents something beyond human understanding, and is often referred to as this white light, which you can certainly visualize. Some of us look further at possible interpretations of the Hebrew. When you examine the interpretations, they can mean something different than the original Hebrew translation. My interpretation is that this is the spotlight used to focus on whatever format of consciousness you need, including altered formats. A spotlight that does not judge, and is none of the individual parts, free of any of the many consciousness bubbles we are capable of, but used to focus on each state of being, and the only thing that brings this altered state into your perception and memory. This should be the goal in meditation, to simply experience this magical spotlight. So there is no conscious experience without the spotlight (Kether). Just like this spotlight is lighting up your current ego mind and awareness you use in your daily life. If the spotlight is ON during sleep, you experience and remember your dreams. If you use this spotlight to illuminate your other forms of awareness and consciousness, you can lucid dream, project, and do many other things, in the appropriate 'body' that belongs to each of these spheres. They are separate for a reason.
Many people used this white light visualization, like Edgar Cayce, to set themselves up for proper readings, to guide them, to cleanse them, to be pure and free. And Cayce was visualizing a white light above his head before going into his trance.
Malkuth, for example, is the world we live in, or the awareness of this world and the physical.
Yesod could be translated as Conduit. Necessary to allow the energy to channel to and from your spheres, in the physical case, the Malkuth body and mind.
So, to allow the light of Kether (spotlight of awareness) to activate your Tiphareth (self consciousness), you connect your Malkuth sphere (physical body with consciousness) using Yesod (conduit to focus your awareness spotlight), on the Tiphareth (self consciousness). This is also straight down the center, or in present time and space. It is now engaged, and you can operate with free will and intent here, and remember things.
I followed that system many years ago, but am rather rusty at definitions and discussions around it.
So forgive any mistakes I have in there. And, this is just opinion, not some expert.
But... yes, just visualizing light makes your right brain produce very weak photon emissions, so something is obviously going on when we visualize light. Photons are energy. So it isn't just wasted visualization.
In addition, if consciousness does prove to be some kind of flow of something tangible, like gravity is a flow of something tangible, then what we perceive as this river or waterfall of energy could be perceived as a white light, because that is simply how we perceive it, and not because it is an actual light.
Perhaps we are simply looking towards the source of it when we visualize like this?
