I’m not sure how useful this is to the topic of light sources - your game world may not use real world physics.
When considering how far light travels, we use the Inverse Square Law. This means that each time you double the distance between the light source, the intensity quarters.
When making a character bioluminescent, consider that any fleshy lightsource capable of illuminating the surrounding environment would be uncomfortably bright to look at, night-blinding those around them.
If your luminance was restricted to something focused and directional, like the palm of the caster’s hand, this may be more practical.
…or just ignore real world physics, because it’s literally magic.