Luster

Electricity is fairly new to Venus, and even so, many places do not have it. In these places, and even in places with electricity, the use of luster is common.
Luster is an abundant, natural gemstone found on Venus. This brittle mineral lacks any sort of useful mechanical purpose, but it has still found its way into many homes. When exposed to light, its use become apparent.
When light is shone on luster, the stone will shine and fully illuminate any moderately sized room. The stone itself will glow warmly with a gentle light, but the room itself will be as brightly as a spring day. 
Homes on the sunward side of the planet will have their luster placed near small windows to fully brighten the room. Heavy curtains can be drawn to cover the window whenever the room needs to be darkened. 
On the the nightward side, a small fire (or any other suitable light source) can be placed underneath the luster to fulfill the same purpose. 
Luster can be found most places on Venus and should be easily available to purchase or scavenge.

Type

Ore/Mineral