All HDRI's are not the same

[glorybound]

I have two versions of a scene, one with a daytime HDRI and the same scene with a night time HDRI. Nothing changes but the HDRI, however, the evening shot renders in an hour and the daytime is rendering in three hours. The HDRI's are from the same photographer and they seem to be of the same quality. Why such a render time difference. Again, the only thing that changes is the HDRI. This got me thinking that not all HDRI's are the same and might be the cause of some of my bloated render times. Is there V-Ray recommended HDRI's?

[Nearl]

Were they the same resolution? I was rendering with some 16k HDRIs and had long render times. I drop the resolution to 8k and my render times sped up.

[Morbid Angel]

Why are you surprised? the daytime hdr most likely has a lot more bright areas that need higher aa then night time since dark values fall into the lower threshold.

[glorybound]

Were they the same resolution? I was rendering with some 16k HDRIs and had long render times. I drop the resolution to 8k and my render times sped up.

Yes, same resolution.

[glorybound]

Why are you surprised? the daytime hdr most likely has a lot more bright areas that need higher aa then night time since dark values fall into the lower threshold.

You might also think just the opposite. It could take longer to clean up the shadow areas in the evening version.

[vlado]

If you can share those two HDRI with me, or at least point me to where I can get them, I will probably be able to tell you more.

Best regards,
Vlado

[psanitra]

Bobby, as Dmitry said, why do you wonder? What you mentioning is pretty much expected behavior. If the sun is directly visible on HDR, you can get easily near 100 000 float intesity on sun spot. For night shot, or human made light you usually get few hundreds. Depending on your setup and how light propagates on materials you need more or less render time for sampler to converge to clean result. Usually one need more time with higher intensity light sources. Unless, you clamp it via secondary rays or color mapping...

[Morbid Angel]

yeah if you want predictable or same render time - fixed rate

[glorybound]

I just didn't expect a 3X render time increase. I'll get the two HDRI's to Vlado.