Why do lights make the model considerably slow?

With large architecture / interior models, you need a lot of lights. The problem is, Rhino models become considerably slow as more lights are added. It’s quite problematic with large models. Can this be fixed?

Using lots of lights in what? And what do you call lots?

Yes, a high number of lights can cause any of the pathtracing style render engines to slow down a lot. This is because each light source is samples each time. Interiors are also at a disadvantage because indirect light makes up so much of the scene it takes time to cook enough samples around the room.

But there are a lot of ways to optimize for better rendering speeds.

  1. Use one of the denoisers. This is one of the best ways to filter out indirect light noise early in the process.
  2. Are there light sources in other rooms that are not needed? Turn them off.
  3. Is there a chandelier or a collection of lights that really could be simulated with one light source to distribute the light, but might use a self-luminant material to look like a lot of light sources?

Any sample models would be great to benchmark if you have one.

In Rhino the problem is already just Rendered mode, written with OpenGL. Many light sources will make it go very, very slow - slower than Raytraced would (but that draws still OpenGL in the background). If you check it in Rhino Render (Rhino 7 onward) you’ll find that the Cycles engine can cope quite well with many lights.

I’d like to clarify I meant to complain about slowness in working views, such as shaded view. Of course render time itself will be longer with more lights.

Here’s one example. This is a public park concept I designed some time ago. There are lights under the large canopy at each section of the pattern, there are smaller and shorter similar canopies through out the park. Also, it has ground puck lights and pole lights through out. The scene is in the center of the park. This amount of lights aren’t that out of norm for what I tend to do, and it gets quite frustrating the working views get slow, not renders.

if your shaded view is using scene lighting, and there are lots of lights, it will slow down. Normally shaded does not, but rendered does, use scene lighting. As pointed out above, that slows down the OpenGL display modes, there is no way around that.


Perhaps I should check if my shaded view is using scene lighting. I just set “Lighting method” as No lighting. Now it won’t be bugged down because of light objects while working (not rendering), I hope? Or am I not understanding correctly what you meant by “scene lighting”?

Hello- yes, that should help, or keep all your lights on one layer and turn that on and off as needed.
Or group the lights in the Lights panel and control them all at once from there.


Thank you for the tip on Lighting Method, @pascal

As for layer / lighting group, well, in theory it makes sense, but it gets really tiring to do wo in practice.