How does bio-luminescence work biologically?
I'm part stickler, part worldbuilder about this aspect of dynamic abilities. Personally, I cannot simply give my character(s) dynamic ability without working out in some pseudo-scientific way how it would/could work on the biological level.
Most importantly for the story, it really helps me understand the limits, positive aspects, and downsides of the character's ability. This is extremely helpful just as a way to round out the character and make the story internally coherent, even if none of the nitty-gritty details make it into the manuscript at all.
So just pushing that back at you, Doodlewriter.

On a biological level, is bio-luminescence similar to lightning-bugs (chemicals reacting to create light), or is it more like a light-bulb (energy current running through resistor, causing visible combustion), or is it a different model entirely?
Because this is supposed to be a give-and-take discussion, I'll drop some of my thoughts on bio-luminescence here, too.
Chemical reaction. We're going to need glands in/under the skin (also eyes if applicable) that contain the chemicals in separate sacs, and then mixing them together in a third sac. Or, it could be a three-chemical reaction: two chemicals in a sac, and when the third is added, the reaction occurs. But that's all semantics. Whatever the case, there's gonna be an abnormal gland in/under the skin that does this - like an extra set of sweat glands all over. Because dynamics are generally born latent (apart from severe pre-parturition shock?? check this for canonicity.....) these glands existed before being utilized. As this is the case, did they perform some function beforehand? Does a person with this latent ability sweat a TON before being activated? Or are these glands just dormant? I think either way would be cool, whether they performed some function before hand or not.
Also, where do these chemicals go post-reaction? Maybe there is a fourth chemical that can be added to the mixture which ends the reaction, returning it to it's original chemical composition...?
Or does it end up being secreted as sweat? What if it actually IS the dynamic's sweat (always subcutaneous when luminescent), and after the reaction is finished, it is secreted just like normal sweat (ie. due to exertion, heat)?
Orrr there's the energy-current-and-resistor model of photon-production.
First off, we have to decide on energy current. Low-voltage electricity? High voltage? Electromagnetic? Magnetic? Friction? For each of these options, and I'm sure there are others we could come up with, there must be a source. The resistors (the element (filament in light-bulbs) through which the energy flows with great resistance, creating light) - the resistors, when active, could be attuned to earth's electromagnetic field..... Or tiny particles in the resistors could be attuned to earth's magnetic north, causing them to seek north [if these (hyper-magnetized) particles were arranged together like the spokes on a swastika (literally can't thing of anything else at the moment) then when actively seeking north they would theoretically spin, producing energy which could be used as current to run through the resistors. This would require virtually no energy from the dynamic (except mental concentration; more on that later), and would thus take virtually nothing out of him/her!].
If it is some kind of electric current that runs through the resistors, however, bio-luminescence could fit as a sub-ability within the larger category of being able to manipulate/control/produce electric current. *shrugs*
That brings its own set of biological questions.... XD
Now I'm thinking of the resistors. What are they? Could they be made up of epidermal keratin? Er, well, the equivalent of what would be keratin on a non-dyno. That seems plausible to me. Or it could be a whole different substance that most people do not have at all. Again, perhaps a subcutaneous gland that stores a certain metal/chemical that most people do not store in their bodies? Which element, when energized, acts as a powerful resistor...?
Now whenever you produce light, there's a lot of energy being talked about usually, so we have to talk about the heat aspect. Where does it go? If it's not an issue, why not? If it is produced, what happens to it so it doesn't get out of control and harm the dynamic? Frankly and unfortunately my brainstorming whirlwind is starting to fade, so I'll just leave those as questions.
Final thing to consider is the element of control. Are the nerves connecting to whatever glands or body parts that are needed for lumination part of the autonomic, sympathetic, or parasympathetic nervous systems?? Is emitting light a fright/flight/fight reaction, or can it be controlled like a flashlight? Is the lumination topical or systemic (one specific body part.....say a finger-tip, or just general areas of the body)?
Can the dynamic with this ability luminate themselves with patterns? Moving patterns? (Talk about black and white paintings/movies being taken to a whole new level.)
Oh, and what about colors? Is this light white? Reddish (because of blood in body)? Or can it be any color? (In which case, full-color movie-screen right there....

And super-camo ability...)
Whew. I think I'm done now. Man, that felt good. I haven't been "creative" like that for a long time. I need to do that more.
Anyway, that's my take on the biology of bio-luminescence.
I am interested, though, in your take on applications of this ability, Doodlewriter. Can it be weaponized (ie. hyperluminescence....laser beams)? Or were you thinking more of a low-key "side" ability (ie. "Hey let me turn myself on for you all!" *lights up hand and waves*)?
Areth,
Ka