Diffuse IBL lights are exported as Lux 'infinitesample' lightsources.

They might as well be as accurate as possible. You'll still probably want to adjust the gain in Lux a bit, but it'd be nice if the first view of your image in Lux was pretty close to the target exposure. It's no trouble to make an adjustment to see if it's better and if everybody shouts at me I'll put it back to what it was :-)

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