No doubt many have wondered as to what are the Ultras exactly, are they simply composed of photons or is the term 'Beings of Light' just a simplification of what they are exactly. While it is obviously impossible for one fan to simply have this answer, I can however give my own two sense on the matter.
Please note that this Blog concerns only the Ultras of the Showa Universe and all related Universes.
Beings of Light or Beings of Matter
Now one must wonder, what exactly are the Ultras composed of, we know light is a major component of what they are but is that all? I doubt that...
My reasons for this come from parts of Ultraman Tiga and Max, when an Ultra is defeated in those series (do note that Max is supposed to be an alternate Showa Universe) said Ultra fozzilized, that is they turned to stone/bronze. Now if they are simply beings of light they should have just faded, but even in the Showa era a fallen Ultra's body was still there when defeated. Now for this to make sense it would mean that Ultras are primarily composed of solid, conventional matter, the loss of required energy means that their bodies were fozzilized when their bio energy fields, which are photon dependant, collapsed, leaving behind only the matter that composed their bodies.
From Human to Ultra
Now I'm not going to talk about the Ultra's human hosts or forms, I have enougth theories about that to hurt my head and probably yours. What I am going to talk about is the transition between the Ultras Human like ancestors to their current forms.
Now let's imagine that their ancestors had the same basic types of biologically relevant molecules that we have, Lipids(Fats), Proteins, Nucleic Acid (DNA) and carbohydrates. It has been shown in several pictures that can be found on the site that Ultras have rather human like anatomies. Taking into consideration that their ancestors were probably more advance than we are it can be noted that the Ultras are probably quite human like ignoring some obvious differences. In fact, their mouths are like vestigial tail (the last bone in your spin is curved like a tail, scientist theorized it is from a left over gene) a trait that is there but no longer used. In contrast, the other members of the Ultimate Force Zero lack mouths to reflect that they did not originate from human based life forms.
Also note that as a rule, one I suspect the Ultraverse follows, any alteration to a subjects DNA after the first 48 hrs of gestation (since being conceived) is fatal. The only way around this is to change every single cell at once, or the old cells and new cells will fight and destroy each other. This would mean that the Plasma Spark changed every cell in their human ancestors, near instanteously, but it is unlikely that the Spark would simply rearrange their DNA, that wouldn't mean that they would change into Ultras, it is more likely that something was added that cause their forms to change into Ultras.
Has anyone ever wondered what this stuff is, I know I have. From what we know all Ultra Beams appear to be based on this substance and since all Ultra Beams are reflective of an Ultra's Inner Light, it is safe to assume Specium can be found in every single Ultra, implying there is great importance to it. We know it is found in abundance on mars, which has little to no atmosphere and protection agains the suns harsh rays and cosmic radiation. My theory is this, Specium is a mineral that is reactive to light, in its natural state is may be akin to plasma (a charged high temperature gas). This would make it the perferct substance to use in the Plasma Spark since it job is to be a replacement sun and it could also explain it presence in Ultras. My theory is that the Plasma Sun and the Advanced humanoids' biologies caused their cells to metabolize and assimilate the Specium that was in their body, or the very least the Specium was implanted into their cells, into most or all of their biologically relevants molecules, near instantaneously, causing the change that made them Ultas.
Now if human cells suddenly had Specium as a major chemcal componenent, that same way we have phosphorous as a major component (It is part of what makes your cell membranes and DNA) how would that affect us if that element with those properties was in us? What would happen to us, what would happen to our cells?
Light Cells is a term I like to use in my own fan fiction but you can thank Ultraman Cosmos and Chaos Header for it. Why do you ask, because there are two major types of cells in this world, Animal/Plant cells called Eukaryotes and single cell organism cells called Prokaryotes. Chaos Header is a Light Virus and when first shown it was seen to be an organic globule with an photon aura. This would not matter except that Cosmos was shown to have a similar energy signture since he was a 'being of light' as well.
Now let's assume all Ultras are like Cosmos, he has the same three minute rule as the Showa Ultras, if all Ultras have Light Cells, then the structure of Light cells may allow them to live as giant comfortably. Light Cell Bones and muscles must be vastly superior to normal carbon based lifeform cells. This may also explain the Ultraman Factor, a human with cells who share normal traits and Light Cell Traits and would back up the theory of Ultra cells.
In the English Dub of Ultraman Tiga (Don't scream your head of), while they came up with many unneeded explanations for Tiga's techniques (Luminizers...? Really?) one theory they put forward stuck with me. For Power Type, Tiga's "Z" or Light Cells became much denser than before and in Sky Type is cells vibrated at a faster rate, which actually makes some level of sense when I think about it. Multi Type is clearly a balance between the two and the combination of these traits maybe what make Ultraman Zero so powerful (I still think he's too powerful).
The Light Cells may have also called for the changes in anatomy between human(oid) and Ultra, such as the Ultra Armor, head Crests (most primates have head crest on their skulls so we may have the gene for it as well but it may be dormant), an Inner Light in place of blood and an advanced nervous system (nerves and brain) granting great mental powers.
I am just a fan and Ultras are just a work of fiction, one I love very much, so I cannot sit here and claim to be the be all and end all of Ulta knowledge. My theories are just my opinion and perhpas my own personal like of trying to make sense of things that don't really need to be understood. In all honesty I don't want to know exactly how the Ultras work, it is that mystery that makes them mysterious in a good way (Did we really need the Midi-Chlorians?). So safe travels to everyone!