During Biblical times, small oil lamps were used to light the inside of a house. But, in order for them to be most effective, the lamps needed to be placed in a location where they could light the entire room. This was accomplished by building small niches into the interior walls. These niches were above head level and were just large enough to hold a small oil lamp. From that location, a lit lamp could provide light to an entire room. As Jesus spoke in what is commonly called the "Sermon on the Mount", He said:
You are the light of the world. A city set on a hill cannot be hidden. Nor do people light a lamp and put it under a basket, but on a stand, and it gives light to all in the house. In the same way, let your light shine before others, so that they may see your good works and give glory to your Father who is in heaven. - Matthew 5:14-16
The picture at the top of this post is of a couple of small oil lamps very similar to what Jesus would have been referring to as He spoke. Knowing the details helps you to better understand the Bible accounts.
(I took this picture of the lamps while visiting the Israel Museum in Jerusalem last year. If you are reading this post via email, you will probably need to click on the title to view the post from the web page to see the image.)