A standard campfire base is 1 × 5′ square. It sheds bright light within a 10’ radius and drops one light level every 5’ beyond that. A campfire can be seen from very far off, but it is not illuminating a very large area. Every time you double the area of the fire, double the range of the light levels.
Campfires provide DR10 within 5’ of the fire when calculating cold damage from environmental factors such ambient temperatures, and drops by 5 for each 5’ beyond that range. The larger the fire, the more heat is generated. Every time you double the area of the fire, double the range of the heat levels.