That's flux density.<quoted text>
The more inane Dave's comment, the more fundamental your answer needs to be, which is what most of us need to read.
Polymath's posts are aimed at the first year science student. He tells you that magnet aligned oppositely have less pull on a third object than magnets aligned alike. That's pretty elementary. But it needed to be said to Dave. Again and again, and to no benefit to him. But if you read the posts, you learn.
It's the same with your material. It varies from basic to intermediate. That's good.
Each magnetic flow or electrical flow starts and returns to the same piece of matter. It is a polarity relative only to that chunk. Because it is the internal equilibrium of the atomic structure of that chunk was disturbed and seeks equilibrium through the negatively charged outer skin, I went into more detail on this in the past.
Because this occurs on a atomic level, this charge has a limited path to follow, and each charge path is individual on this magnetic flow basis. To get strength, they have to be in parallel. These are tiny streams kept isolated by them repelling each other, but the real strength is the difference between the nucleus and electron shell caused by the disturbance. It's a pump. Being caught in the flow is a lot stronger than the effects of being next to it. When this flow encounters another object, it works on the atomic level because of these individual paths. Matter can not create a monolithic field of this charge movement because of that. Hence the need for parallel flows to increase relative strength. This magnetic force is more direct than an electrical flow. A magnetic flow passes through everything. If something can't get out of the way fast enough it gets bumped by it.
The power in a magnetic flow is derived directly from forces within the atom, as are the paths.
Electrical flows combined differently. Those are bumped electrons, by a magnetic field passing fast enough, or changes similar on the chemical level. This alters the nuclei and electron relationship, creating that charge imbalance that produces that magnetism. However, this is closed loops, resulting in potential differences. This is why when you add batteries or magneto generated voltage in series you get an increase in potential difference between the terminal poles. This difference adds more strain, so to speak. The positive of one is sucking off some of the flow of the next battery via the negative, which then combines the two, or more, adding voltage.
Magnetism is like batteries in parallel. You have more mass to flow, but you are limited by the inherent charge difference within atoms. This is the same thing you have with batteries. In parallel the voltage stays the same, but you can draw more magnetism. But adding batteries in series adds those charge differences as you add those loops. I'm not going into the details of that now.
But the amazing and astounding thingy is under enough stress, this charge movement wraps this magnetism up in loops and kicks them out as light. This is stress caused by things like motion fighting gravity and heat. Some of that excess heat is transferred into those loops as energy. This energy can then transverse the universe and be transfered to far distant pieces of matter, thus effecting roughly the same process that transformed it. Stand in the sun for a while, or put a thermocouple in it and read it to understand. That heat in excess of the ambient temp is coming from EM bombardment. Heat doesn't transfer via conduction across a vacuum like space.
So the reach of EM, and these loops are carrying energy mucho,muco stronger than gravity, and can have much grater effect depending on how it is channeled on the receiving end.
Your light "particle" is carrying the same energy it left with. The difference in "strength" from a distant source is due to the density of the paths lessening.