Many light sources, such as the continual flame, dancing lights, and light spells; and a everburning torch, sunrod, and torch; all shine bright light for 20 feet, and an additional 20 feet of dim light. A candle sheds dim light in a 10-foot radius.
But how much light does a bonfire produce?
Unclear according to the rules as far as I know. The simple answer would be as much as the GM rules it produces, using the 20 feet as a sort of minimum.
After all there are a lot of factors to something like a bonfire that could effect it's light. How high is the wood stacked, what kind of wood is it, is the bonfire roaring or just sort of smouldering.
Usually I'd say you would have bright light out to around 30 feet, then maybe twice that in dim light, but that's just my opinion.
Generally any light source that isn't codified in the rules is strictly up to the GM to figure out using their best judgement.
Any sort of environmental lighting is subject to the designer of that environment, expect table variation.
That said, a large fire built for light should at minimum produce as much light as a torch. You'll just have your players double-taking and laughing at you otherwise, and nobody wants that.
But how much light does a bonfire produce?
Well it depends on the size of the bonfire [width and height], the material it's made out of, any extra accelerants used, oxygen availability, atmospheric conditions, elemental convergences, errant fey, divine whimsy, ect...
However, who's going to math it out? The easy answer is 'as much as the Dm wants it to' or if it's PC's building it 'how far they want it to, limited by how far the Dm wants it to'.
It's a case by case basis, but if I were the GM giving an off the cuff answer I'd say 50ft bright light and another 50ft of dim light.