Sea light
During the day, the light of the sun allows communication using MOSEA from any of the Sea-towers. But during the night, when the sun is no longer present, a special device needs to be installed to allow people to keep communicating with the language of the stars instead of the Sun. A good fire can give a decent amount of light, which can be amplified by the mirrors and potentially used. This is okay to use to signal the position of the sea-tower, but it becomes problematic with the panels to color and codify the messages themselves, as fire can spread to the panels and destroy the colors.
Fortunately, in several of the oldest Sea-towers, a gift from the ancients was discovered. Those sea-towers could capture the light of the sun and use it to provide light to the mirrors while under the influence of the stars. So it began the communion to learn how this system works and how it could be replicated.
A top layer, similar to a thin mirror with different cells inside, collects the power of the sun instead of reflecting it. This element can't be replicated yet; it needs to be extracted from the ancient ruins.
Two small grey boxes, which go on the sides of the main mirror, detect the power of stars to activate the system. If the specific box is damaged, it can be replicated using ceramic, but it is slightly heavier than the original ones.
A backbone of purple synt, which is connected to all the elements, and none of them will work without it, but its exact function is unknown. This is unsurprisingly the trickiest part to locate and make work; it is also the most dangerous to manipulate.
A synt filament, the brightest ones are the ones found in the ruins, but normal metals can be used as well if they are thin enough. They are less bright and break more frequently.
A normal capsule of crystal to surround the backbone and the filament. This is needed for an exquisite craft piece, but it is by far the easiest element to replicate. Once complete and attached to the backbone, it will become one with the top layer. If this step is completed at sunrise, that night the new Sea light will shine for the first time. If this is not the case, its light will not shine until the following night.
I like how this idea seems to draw from modern day light houses. I find it clever that you repurposed it for your world. but as some suggestions, I think it would help if you gave a link to the MOSEA article, (if you've written one) just to help make it feel more apart of the world. (Links and such tend to help with that), but "similar to a thin mirror with different cells inside, collects the power of the sun instead of reflecting it." Why didn't you just say solar panels? of course, those are super little picky things, and are not important and do not ruin your article at all. I thought it was a smart and clever use of modern day technology. And I'm intrigued by the language of the stars and the sun. I will definitely be checking out more of your world!
Thanks for the feedback. good catch on me forgetting to link MOSEA. I will do that, after the ceremony. In the meantime, this is the article for it: https://www.worldanvil.com/w/laria-s-ninth-world-laria/a/mosea--language Regarding why not calling them solar panels. I more or less try to avoid using our own words for things, in this article, as they are written from their perspective. I will need to name these things at some point. I'm glad I described them well enough, you were able to catch what they are.