First, he said the object of the riddle exists our world, not just our language. But I'm assuming he means the generic type (i.e. sword).
Well on my understanding, he explained "words of our real world", specifically when I started shooting Ithlinne prophecy and then Nilfgaard.
Again, it's my understanding that light not stands for light sword neither the weight. But related to the sun, fire, ray of light, lux aeterna whatever />
Probably that "darkness" is related with the Dark mode.