Fake fire

Refined navias (powder made from rocks that are mined in the Navian mountain range).

The navias is transported in its rock form, in blocks about a cubic meter big. First it's crushed and put through a grinder until is really really fine (though not fine enough to dust). Then the powder is filled into airtight containers which are locked away from civilisation.
The more the stuff is handled by people, the less refined it is. So during production and mining people need to be careful to wear gloves and keep their distance.
The absolutely refined stuff that's not handled by humans at all ever releases a silver light when put into a holder with the proper rune. The less refined (=cheaper) stuff goes in gradations of blue to green to orange to red (=the really cheap stuff that's been directly grabbed and handled).

The castle bulk orders it from a specific production team like 2 years in advance because they want the really pure stuff.
Anything purer than yellow needs to be specially ordered and transported. Yellow is basically only used in the mines themselves and red is the stuff that normal people would buy. Like in markets and stuff.

Its value is directly proportional to how refined it is, which includes how long it's been locked away in its airtight container.

Only royalty can really afford silver light. Otherwise you'd have blue light affordable for nobles, green light for merchants (carriages and boats as well as their homes), and yellow light for city administrations that can afford it and want a safe alternative to fire. Red light is cheapest but still more expensive than a candle or a fire. You'd have richer working class using red lights and the poorest using normal fire.

Pretty common, actually. High demand for navias, though the miners wouldn't know.

Safe lighting at night

The powder is put into special holders that cause it to glow when it's dark. (the holders have a rune on them that directs this, but most people don't really question how it works). The more people walk by it every day, the more often the powder needs to be switched out.

Navias
Metal (for the holders)

Fine powder, more like sugar than like flour.

Packs of powder come in three different sizes: small (like a ping pong ball), normal (fist-sized) and large (grapefruit).

A holder with a normal pack will weigh about as much as a baseball bat (because the holder is metal).
Small - weight of a peach
Normal - weight of an orange
Large - weight of a grapefruit

The powder is a nondescript grey colour, tinged in the colour it will eventually glow in.