Slow render times

A user wrote:

Any thoughts on the slow render times?

The time that the rendering engine takes is based mainly upon the number of:

Triangles
Lights sources
Reflective surfaces
Reflective bounce limit
Refractive bounce limit

Triangles:

When we first wrote IRender, we only rendered one side of the triangles. That's the way most people modelled back then, to render efficiently. If you wanted to see the back side of a surface, perhaps reflected in a mirror, you had to add a second surface to represent the back side. Because so many users do not model this way, we added the option of rendering 2 sided triangles. That option is on by default as a convenience to make sure that new users get the result that they expect, but it does possibly double the number of triangles in the model to be rendered. That can be set here, to go back to rendering only the the side of the face  with a material defined (or the "front" side of faces with no material defined):

Using the Bump Map or Displacement features for materials will also have the effect of creating many more triangles to be added o the model for the rendering.

Light sources:

9 times out of 10, when someone sends me a model that is taking forever to render, it turns out that they have created too many light sources. You can check this by looking at the Statistics of the rendering, either while the rendering window is still up, or by looking at a saved JPEG file of a rendering. The Statistics for a saved JPEG can be viewed using the Options/Image/Edit/Query:

The usual cause for having a large number of light sources is using a material as a light source on a surface that gets broken up in many light sources at render time. In the example above, I made the bench a light by making its material illuminate. That added 30 individual light sources to the model. It is much more efficient to use object properties to make an object a single light source, rather than using the method of setting a material to illuminate.

The other thing I see are some chandeliers which have multiple light bulbs, where because of the particular view, the chandelier could have just been used as a single light source.

Reflective surfaces: Making surfaces reflective which do not need to be will also increase rendering time. Turning off Auto Reflection might help for some models. See:

http://www.renderplus.com/wp2/wk/Auto_Reflection.htm

Reflective and Refractive bounce limits: These limits are set low by default, to keep the rendering time down. Increasing these limits will increase the rendering time.