For ships and bases, my understanding is that it could be described by:
The damage from each non-armor-bypassing weapon hit is reduced by X, for every hit on the ship, until this component is destroyed. (Only the highest-rated component with this ability on the ship/base has this effect.)
So, if you have unmodded Emissive Armor I (EA 10 and structure 30 on a component that is always hit first), then:
* You can shrug off an unlimited number of weapon hits that do ten or less points of damage each, no matter how many times you are hit, even by the same enemy during the same turn (exception - fighter Groups combine their damage, meaning a larger fighter group is more powerful
).
* If attacked by an enemy ship with weapons that do 15 points of damage, each one would do 5 points of damage to your armor. It would take six hits to destroy your single EA I component. If you had two EA I components, it would take another six hits to destroy the second EA I component. A single 70-point hit would be exactly enough to destroy both EA I components.
* If your ship had one EA I component and one plain Armor component with 40 structure, then there would be a 50% chance you would lose the EA I after six 15-point hits as above, and a 50% chance that after eight hits you would lose the plain armor, and then it would take another six 15-point hits to destroy the EA I.
PvK