Managed to halve my render times with 1 button


Just thought I’d share this here. Who’d have thought specular could be so nasty…



Interesting Video!
Did you test the renderspeed by turining off the specular component of Beckmann, GGX, etc. and replacing it by a specular-only BRDF such as Blinn? My guess would be that this would make a similar difference.



Yes, oddly you get different render times depending whether you set the specular strength, the specular brightness, or the specular checkbox on the lights. The one which gives the biggest speedup is to turn off spec on the light sources entirely. So long as you keep in mind to add some sort of reflection to make a highlight, and use pbr lights or similar, you can save a significant amount of render time.

The actual project I discovered this on gave an even bigger speed up but unfortunately I’m not allowed to show it yet. It took my render times down from 1 hour 15 minutes to around 20 minutes each. From now on I’m more or less turning off specular on every light source if I plan to use rough blurred reflections.

The only downside really is if you are using omni or spot lights with a BxDF reflection-only material workflow. In these cases the specular highlight is the illumination, but that method is pretty rare and advanced… and slow as hell.


Interesting. Thanks for sharing!


Turning off Specular light will result in a very dull rendering.
Doesn’t work for me.


Remember that specular is just a reflection of a light source. All you need to do is enable the “show in reflection” checkbox for area lights, or supplement spots and omnis with a white luminant sphere. The test scene below has 100 spotlights shining down with and without specular enabled. 7 minutes vs 13 minutes. I’ve made everything extra glossy to try and exaggerate any specular.

The key is to stop relying on specular in the first place. sure if you take a scene you’ve made and just turn spec off then things will likely get a bit dull, but that’s because you will have made your materials and lighting assuming spec will be used. The same as flicking GI on or off after a project is finished would result in poor lighting as the scene will be made with assumptions about whether it will be used. My general suggestion is more to consider making scenes from now on without any specular highlights, instead start designing them to just reflect real geometry instead of slapping on giant specular smudges to emulate a reflection.



Thanks Mash, another great tutorial.
Look forward to trying it out.