When I F12-render a scene with a mix of Octane world-light and added lamps (Octane materials), the F12-rendered image is 4 or 5 stops brighter than the Viewport render. Plus, a black and white image gets pink(ish).
What's wrong?
Color Management is set to None.
But the difference between the two renders is - literally - like day and night...
The overall image quality of the Viewport render is also richer; there's more contrast but at the same time a wider dynamic range; more definition in lights and shadows.