The feat reads as follows:
Brighsoul
The fire inside you asserts itself as beaming, radiant light. Your body is naturally luminescent, glowing with the effects of a primal Light cantrip. A cantrip is heightened to a spell level equal to half your level rounded up. The light is involuntary and constant; if counteracted, it returns in 1d4 rounds. You suffer a -2 circumstance penalty on Stealth checks to Hide or Sneak and gain a +1 circumstance bonus on saves against light effects and effects that inflict the Blinded or Dazzled conditions.
If a creature under the invisible condition were to use the Hide action, would they still apply the -2 penalty to their check?
Logically speaking, if the invisible condition implied just that the light passes through a creature, that does not prevent the creature from producing light, so it would make sense to apply the penalty.
However, if the invisible condition suffocates any light emanating from you or just magically prevents other creatures from seeing you, the most logical conclusion would be to not apply the check.
What is the general consensus on this matter?
PS: While Brightsoul is what arised the question, this would also apply to things like someone wearing an armor that has been targeted by the cantrip Light or any other effect that causes the invisible creature to emanate light.
Best Answer
You're an invisible light source
You can be both invisible and emit light. All light passes through you, but that doesn't stop light sourced from you from being produced.
The Invisibility spell is clear on this interaction (and while the Invisible condition need not follow those rules, there's no reason not to apply it):
In practice, I'd consider the light to remove the major benefits of invisibility; you shouldn't be undetected by default, requiring a seek to find you, because "undetected" implies they can't even identify the space you occupy; your invisible body means figuring out exactly where you are is more difficult, but it's very easy to pin down what space you're in (frankly, it's kind of ridiculous how low the penalty to Hide/Sneak is; the only place you could conceivably hide effectively would be behind cover in a brightly lit area).
A reasonable way to adjudicate the combined effect would be to treat you as Concealed; you're not truly invisible, but it is harder to get a bead on you when you're just a light source with no visible body. You're harder to target than if you weren't invisible at all, but still easier to target than invisible or hidden creatures.