Cycles fireflies with police lights setup For an animation project I'm working on, some vehicles with a warning light - these plastic ones with a rotating mirror inside which you can find on top of police cars, firefighter trucks (blue) or excavators and construction trucks (orange).

Some time ago I read a question (I am not sure if it was on stack exchange or somewhere else) where someone wanted to create glowing buttons. The answer which was given to him was something like "cycles is a physically-based renderer, so try to model like in the real world". So the solution for that was to model a button and put an object emitting light below.

With that answer in mind, I modeled the light as it looks like in the real world. A basic plastic casing with a separate transparent part (Glass BSDF), the mirror (Glossy BSDF) and a kind of light bulb (Emission). So far so good. The problem with that is, you need an unreasonable number of samples to make it look alright. You can have a look on my results below.

256 samples, 960x540 (25% of 1080p) - 0min : 31sec


1024 samples, 960x540(25% of 1080p) - 2min : 34sec


4096 samples, 960x540(25% of 1080p) - 8min : 12sec


This example scene has only ~1500 verts and the same for the faces. The vehicles I made have up to 80k faces and there is also a landscape around.

My question is: Is there a better way (in terms of rendering time) to achieve the same or a similar effect?

Thanks in advance
nioerd

--- edit ---

An image how the scene looks like with the changes suggested by pycoder (change the glass material of the bulb and the hull to a material which is only viewable for the camera)

256 samples, 960x540 (25% of 1080p) - 0min : 30sec


I can't see any real difference between my first try and the suggestion by pycoder, except that there is no illumination from inside the hull. Even the time needed for rendering does not realy changed. Did i do something wrong?

--- edit 2 ---

Added the model to download via blend-exchange.
In the glass shader you need to use the light path node. Setup your material so the main section gets mixed with a full transparent shader by way of the camera output of the light path node.



This will make your glass look like glass when the camera sees it, but not even exist when other objects see it. Doing the same with the bulb and then adding a point light would also be an improvement to sample count.

Note: This is not physically correct. To get better render times from cycles, you need to pull tricks like this to improve sample count.

Edit:

After playing with your file I got this (25 samples):



Here's what I did - switched device to CPU and disabled reflective caustics. (I also did a little trick with smooth shading to improve the look of the siren, but that's another topic.)



Here's the new blend: