When you adjusted the HDRI so that other added light sources would react more realistically (the candle) it was an outdoor scene. So making a sun to about the same values makes sense. How would you do the same process for an HDRI that was an indoor scene, so that the lights you add are also physically accurate?
Good question! I don't think you're ever going to get it to be exact, but you can use the same trick of comparing it to a known source. If the sun is coming in through the window or if the sky is the dominant light source, then there is no difference in practice, but if it's indoor lighting only then you could go based on average recommendations like the list below:
Source: Lumens Per Square Foot: Recommended Amount Needed for a Room - The Home Depot
Again, you probably don't need to be exact and if you only have one light source (the HDRI) then it doesn't matter anyway, but if you have different light sources then it helps to at least be in the right ballpark. Hope that helps!