The lamp is a non-upgradable feature of your campsite. It provides light during the nighttime hours and, according to your character's in-game dialogue when you click for Info on the lamp, increases the security of your campsite.
The lamp can be lit at the cost of resources. To light the lamp costs the same amount of resources as the campfire, and lasts for the same amount of time. During this time, the lamp will appear to go out during the day, but the light will return again at nightfall.