In one of my settings people use mori rock, a softly glowing mineral that glows brighter when struck against a hard surface, and can be used as a hand held staff or in a larger quantity as a street light.There are several different colours of this rock,and in city street lights each signifies a new area of the city.The rock will not start fires,and if looked after well will last for decades or even centuries before it needs to be replaced.1xp

Whale oil--imagine a whale with a derrick on its head... One city in the Byzant Empire uses natural gas to light up the city streets. Some of the larger Elven homes are open enough to allow a minimum of light to be used within. The Elven Homeland has a nice climate year-round, so spacious homes with lots of windows are feasible. Also, some homes are designed to allow the maximum sun &/or moonlight in, with carefully placed skylights. There have been a few recent discoveries of ancient Dwarven mountain kingdoms (lost during the oppression by the Olde Empire), that used a form of fiber optics to channel light throughout. Mostly, everyone just uses good old fashioned fire for light, whether in the form of kerosene, coal, whale oil, candles, or wood. Throughout much of the more heavily Gothic cities of Formour and Byzant, the cities are lit most of the night by shops open late, with normal flames (lamps, et al) providing enough light to navigate to it.
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In one of my settings, weak wizards could find a good job at going around town, and lighting 'lanterns', i.e. rocks on pillars, with a Continual Light Spell. That spell would make them glow for several days, and if the wizard was especially successful (critical success) they'd most likely become permanent.

In the worse parts of town, the lighting tends to be more sparse, as most of the 'fireflies', as they are called, don't go there, run through there lighting a few lights, or get mugged/beaten/whatever on their way (being a wizard who lights steet lights implies that you don't have the magical power for a better job).0xp

In a realm I was contemplating, where magic is just another skill, low level spells are pretty common, and just about anyone with a brain has one to three of them that fit their job, many people would have "Light 1". While this would normally create a ball of light suitable for reading for an hour or so, if cast upon a prepared globe, it would last for many hours.0xp

I was just thinking, if there is a relationship between magic using and showmen/ entertainers (so magic would generally be pretty weak), then there might be an entire "class"/ profession of magic users who do nothing but stage craft magic. These guys would cast a light spell on a mirror, and use their control over it to run the "lighting" for a show.

An interesting thought. Hmmm. This is one I have to contemplate more.0xp

Gas Lamps
These are not the gas lamps you are thinking of. Every building has a steam boiler to generate hot water and steam for heating and other purposes. So every compound will have its own lighting system.

The steam heats coils in a glass "jar". The "air" inside the jar is a combination of noble gases and some base chemicals. When the gas is heated enough, it begins to glow. Thus there will be streetlights, house lights, and hall lights, in most buildings and compounds that have a boiler.

In most cases, these lights are not used in personal spaces. It is only recently that shutter systems are used to cut off these "lamps".0xp

Some other ideas:

1. Captured magic creatures which glow - from enhanced fireflies, elementals, etc. I think using crystal spheres with glowing spirits trapped within appropriate for evil lairs anywhere. They can even be broken to release reinforcements.

2. Fragments of pure Elemental Fire can be used perhaps located very high on spires similar to the lights in larger parking lots. Being quite bright and covering a large area, you would not need a lot of them. Since the Elemental Fire would be valuable to many spellcasters, they would need to be protected against theft.

3. Bagdad Batteries can be used along with primative light bulbs to provide lighting much as we do today, with only minimal anacronism :) There would be a whole guild devoted to the operation, refueling and maintenace of the system.0xp