Under most V-Ray lights there is a U and V parameter present. Using these values to adjust the size of your light instead of just scaling will produce more accurate results and correct output values and not to mention faster render times.

Incorrect Scaling Causes Noise

The following renders are done with low anti-aliasing in order to show the difference between scaling your light with the scale tool (or via the attribute editor) and adjusting UV parameters.

Using physically correct scene with a basic sun + sky setup, I have cut a window behind the camera. To this window I have added a V-Ray Rectangle Light (V_Ray_Rect_Light) and scaled it using the scale tool to cover the window.

The portal light that has been scaled using the transform properties and produces quite a bit of noise

As you can see it is very noisy. Not exactly a good clean render! Now lets compare it to the exact same light that has been scaled with the UV parameters instead.

As you can see it is still noisy for the sake of the expirement but notice that the shadows are much cleaner on the back wall compared to the other image?

It is not even necessary to compare these images side by side as there is such a big difference. This should also apply to sky portal lights that have “Store with Irradiance Map” checked.

Also, notice the render times are much faster by using the UV method of scaling lights? Even in our dirty scene there is a 9 second difference, which could turn into hours of render-time saved with bigger projects and animations.

Incorrect Scaling Also Causes Incorrect Intensity

Although a little more obvious, another thing to remember is that the light’s intensities are also affected by the way the lights are scaled.

To our same scene I have added a basic 2450 lumen light above the statue. The light is 200cm x 20cm and is scaled to this dimension using the scale tool.

This is not really working!

With a camera of F22, Shutter Speed of 6 seconds, ISO 100 – there is way too much light being emitted!

This is because the scale of the light’s transform node is affecting the size and intensity of the light, whereas the UV parameter of the light is only affecting the surface area and not the intensity of the light itself.

Below, the UV parameters have been used to set the light to be the same size of 200cmx 20cm. We now have a much more respectable result.

The area light on the ceiling can now be considered physically correct since it has been scaled using the U and V parameters

Anyway, I’m trying to find a nice setting for the mia_material_x mats for foliage/leaves in mental ray. It’s quite difficult to find settings that look good through various lighting conditions.

Sunny day

Under a pale grey sky

This is looking OK, but there are three key ingredients to get really nice looking leaves.

• Decent diffuse texture
• Appropriate amount of reflection/gloss
  (obviously heavily depends on which species you are trying to create)
• Decent translucency texture

For mental ray specifically:

• Translucency value must to be always at 1
• Transparency colour must be set to pure white (1.0, 1.0, 1.0)

Image sourced from http://sor.typepad.com/

Once you have this basic it’s just a matter of tweaking the gloss and reflectivity settings until you have a nice look for your scene.

Unfortunately I have not found a “universal-looks-sweet-on-every-scene” setting yet…