Underwater Light?

I’m trying to make an underwater light source, and it seems to work fine in eevee, but when I try to do it in cycles, it completely fails, and I can’t figure out why.


Cycles (with the light turned WAY up to like 800 watts instead of the 50 watts used for eevee):

I extruded my ground plane to make it into a solid, and created my point light in the middle of it.

Here’s the nodes for the water material that I used for the solid I created:

How can I have cycles make a small light in the water? I tried adding a volume shader to the water, but that made everything worse. I also played a bit with the anisotropy of the water, but didn’t have any success there.

It is a bit frustrating that every time I switch between cycles and eevee, I have to reconfigure all my lights!

Oh. Forgot to mention. I did try sticking a transparent sphere around my underwater light like I did with my lamps. That didn’t help, either.

did a quick test for cycles rendering lights underwater; here are the images:

As you can see there are two images for each of three viewing angles. The top row uses the setting you posted above while the bottom row uses settings which, in my opinion, more accurately reflect how water refracts light (and no I didn’t play around with the IoR so it’s not 100%). While it is difficult to see the lights at the oblique angle you can still see the spot, area, and point light sources in all 6 images. you can also see the effects of the Sun light source in the oblique images.

While it’s worth pointing out that Eevee treats sun lights more like area lights the thing that stands out to me is that, It is likely not you lights and/or water material that are causing your problem. So, I would suggest having a look at your fog material as volume shaders are, at least for me, really hard to work with in cycles.

What are you trying to accomplish?
Blender Cycles is physics, you should know how light interacts with material transitions. Whereby the refraction index (IOR) is important.
Maybe a quick fix would be to make water 100% transparent and reflective.

Goal is to have a light in the water. So, like something glowy is swimming down there, but you can’t really see what it is.

The eevee version is similar to what I’m wanting, but I want to see how to do it in cycles as well.

I think I have the water completely transparent and reflective, don’t I?

I think you need to study about the nodes “Layer Weight” and “Fresnel”.
Both are ways to calculate the lightray reflections in relation with transparent materials (water).
It’s not easy, because you need to understand light physics and how blender works with them.


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