I’ve been using IBL+FG to get an overall illumination in my scene, now I know I can create something similar with an array of lights as well. Is there a point where the number of lights would be slower to render than just using IBL+FG? If so, what would that number be?
I understand there may be a broad answer to this question, but a general rule would be good to know. As I’m trying to figure out the calculation value for each method.
Thank you!
While rendertimes are certainly a factor, I would also consider the manhours involved. If you want something that looks photoreal, it far faster to do it using IBL than to manually light the scene using traditional lighting techniques. Your rendertimes may be slower, but you can wait for the renders at the pub 
sorry for the delay in reply, I’m having difficulties with my Internet connection.
yeah i’ve always appreciated the simplicity of it all, but for my own knowledge and for a better understanding of lighting in general I thought it would be good to know.
Is an IBL+FG considerably slower than a similar effect achieved by an array of lights? (and again is there a limit?)
I personally haven’t found them to be very slow at all, but I know some would prefer no FG at all.
thanks.
An IBL can be slow if your setting to get the right detail needed is high to avoid trouble. This is usually caused by a high contrast image in your IBL.
FG + IBL will also not provide you with “correct” hard shadows. Irradiance Particles or Builtin-IBL can provide that but take longer to render.
Lights are fine depending on the type of shadows. Soft shadows are more painful. The reason lots of lights hurt render time is that each shading call will run through the light loop to get lighting information. The more lights, the longer the loop is and will take longer.
Tweaking lots of lights can also be painful.
FG (Final Gathering) tends to be good enough for most things, and maybe a couple key lights for harder shadows. It’s also reasonably fast. I am not sure why anyone now would prefer not to use Final Gathering in a raytracer. Maybe for REYES, but even that has a point cloud implementation that’s fast and easy.
The best trade-off for speed and higher quality is the Builtin IBL unless you have a lot of specular objects. In which case it might cause too much grain. The Maya Rendering forum has a thread on the Builtin-IBL and Irradiance Particles.
I was wondering…a lot of what I’ve come across in books and online don’t speak much about what is going on “under the hood”. I would like to get more in-depth on how a renderer renders…How did you come across this information? is it by reading technical papers? or is there a book I’m missing from my library?
my appreciation for your reply, they have been very informative and I’m sure will lead to me asking more questions on this forum 
I generally keep an eye on technical papers and I ask questions when I can from the sources I know have an idea from experience or from working with the companies directly.
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