They were called Moonlight Towers. I believe Detroit had more than a hundred of them all around the city. They were powered by acetylene gas and gave off a brilliant white light . We had them here from the mid-1880's until early 1900's. Many of the towers were sold to San Antonio where they are still in use with the exception that they are now electrified.

If you google moonlight towers you'll find a ton of better info.