Create Bonfire (XGtE p152):
You create a bonfire on ground that you can see within range. Until the spell ends, the bonfire fills a 5-foot cube. Any creature in the bonfire’s space when you cast the spell must succeed on a Dexterity saving throw or take 1d8 fire damage. A creature must also make the saving throw when it enters the bonfire’s space for the first time on a turn or ends its turn there.
I am aware that spells only do what they say they do, but usual bonfires do create light. While illumination is not mentioned, it is hard to imagine a bonfire without flames and light, and the spell does not indicate in any way that this is not a usual bonfire.
It should be brighter than a torch for sure, but how much exactly?