Technical discussions > Lighting

Issue with god/light rays

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Hello! I'm hoping someone on the forum can help me out creating great looking god rays.

A bit of background: I'm trying to create a slide that'll be used by a professor who's employed by a large cancer centre. The slide shows a cell, DNA, histones and closed & open chromatin. I wanted to show real displacement along the outline of the cell and the DNA, and thus created everything in ZBrush, where I also used the noise feature to add surface detail. I started this slide a while ago at a time when KS didn't support real displacement, so the file is unfortunately quite massive. I've put too much work in to go back and remake elements just so I can use the new displacement feature in KS8.

I thought it'd be great if there's a light source behind the "cluster of grapes" aka "closed chromatin" so the rays shoot past it. Because of all the elements I had to put in this slide, and what needed to be emphasized, the various elements are placed quite far apart (as you can see in the 3rd screen shot); I don't know if this is impacting the ability to create god rays.
I've watched Esben Oxholm's webinar on light rays, and I've tried to find relevant videos on YouTube, but I just don't seem to be able to replicate the light rays the way Esben does it. In the 2nd screen shot you can kind of see them a bit, but they're not a pronounced as I'd like them to be.
I know there are technically only a few sliders to play with, but I don't seem to be able to get it right. I've tried many variations...

If there's anyone who's kind enough to have a look at my file to see where I'm going wrong, that'd be awesome. Apologies in advance for the file size (see note below).

I've zipped up the KS file, and it's still fairly large (around 1.6 Gb). Bandwidth is not an issue for me, but I realise it is for some people. I've uploaded it to DropBox due to its size.
Also, to keep the file size down, I've deleted a lot of the "grapes in the cluster" (closed chromatin), but I left the ones farthest away and closest intact in the hopes this will help in determining the right settings for the fog material and light source. The 1st screen shot shows you what the whole slide is supposed to look like when all the elements are intact.

Many thanks in advance!

Hi there,

Creating clear 'god rays' or volumetric shadows in these conditions, namely an open environment, is actually quite tricky. There are many pieces that have to work together to get the best effect. You will have to balance the light source (position and settings), Scattering Medium material and Image Style.

Here are some rules of thumb for creating clear volumetric shadows:

* Use a relatively low density for the Scattering Medium material.
* The final density is controlled by a combination of the Transparency Distance and Density sliders.
* Adjust Transparency Distance first, so that the farthest objects look slightly hazy.
* Adjust Density to fine-tune.
* Use focused light. Light in a narrow beam will create clearer, higher contrast shadows.
* Spotlights and IES Lights are good options for focused light, as they emit light in a beam rather than diffusely.
* Point Lights and Area Lights are diffuse light sources, meaning they emit light equally in all directions. As a result, the volumetric shadows will appear fainter (i.e. more diffuse).
* HDRI lighting also tends to produce fainter volumetric shadows.
* Place objects close to the light source, if possible. The closer an object is to the light source, the more apparent its volumetric shadow will be.
* Use Photographic Image Style.
* Increase Exposure and Contrast for an instant improvement of volumetric shadows.
* Adjust the Curve. Specifically, decreasing Shadows (< 0) and increasing Midtones (> 0) usually gives good results.
I attached a simple example scene.
The scene contains 5 identically-sized spheres that are suspended in a foggy volume. The spheres are positioned at varying distances from the light source.
There is a Multi-Material for the light source to switch between Spotlight, Point Light and Area Light.
There are Basic and Photographic Image Styles.

I also attached a composite of renderings, showing the differences between Spotlight and Point Light, Basic and Photographic Image Style.

I hope this helps.


Hello Dries, many thanks for the thorough reply and taking the time to put together the example file; this I can definitely work with. I'll give it another go this weekend, and if all goes well, I'll post the results in the hopes it'll help anyone with a similar issue.

Thanks again,


Thank you Dries for this example and the explanation.
That should help a lot!


Using a few of those 'rules', I got attached result fairly quickly.

I changed the light to a Spotlight and added a Photographic Image Style.

Good luck. :)



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