Caustics Making things Darker

[dj_buckley]

This isn't necessarily an issue relating to V4 (although I am using it), but I've noticed this previously too.

Can anyone explain why enabling refractive caustics (Caustics 'Slow' in the material), makes things appear a lot darker.

Screenshot attached with absorption colours and light strength exaggerated.  The only setting to change between the two screenshots is the Caustics being enabled in the water material.

Disabling 'cast shadows' in the object properties gives a completely different look again - although I know this isn't really a correct setup.

Just looking to understand why this happens so I can rectify it.

[romullus]

I guess it's happening because refractive material without caustics, gives physically incorrect result, whereas material with caustics, is more physically accurate.

[dj_buckley]

Haha well when you put it like that .... but let's say I wanted the Caustics on the brighter one?

I mean it's a pretty normal water setup to start with No Diffuse, Reflect and Refract both White, Caustics enabled, Colour introduced with the Absorption

[Juraj]

It's the absorption. To make absorption visible with "fake" refraction (formerly called 'hybrid', not to confuse with thin), the value has to be boosted much stronger than the material actually has in reality.
So the value has to change with caustic setup to be realistic.

[dj_buckley]

Thanks Juraj

[maru]

Pretty much what others said. Easy explanation:
If something is darker, it usually means lack of light. Lack of light usually means shadow.
One object casts shadows (and light is visible only in places where it is focused by caustics).
One object does not cast shadows (or rather: it casts very weak transparent shadows).

[John.McWaters]

Thanks Juraj

Were you able to solve this issue? If so, can you post the setting for your water material?