Automatic Luminance or Photometrics automatically adjusts the overall intensity of your rendering, much like the automatic exposure on a camera.

If you want to adjust Lighting Channels or other items without having Photometrics apply, you can lock the Average Luminance on the Lighting Channels Wizard.

Why doesn't turning off a light make my scene darker

The first time I tried out Lighting Channels I was confused that lowering the intensity of a light didn't make the scene darker. The same effect is true when you add or remove a light from your SketchUp scene.

The cause of this is Automatic Luminance or Photometrics

Automatic Luminance or Photometrics automatically adjusts the overall intensity of your rendering, much like the automatic exposure on a camera.

If you want to adjust Lighting Channels or other items without having Photometrics apply, you can lock the Average Luminance on the Lighting Channels Wizard.

In the latest version of IRender nXt we have changed the default setting, so that the Luminance is locked when you make adjustments to lighting channels.

If you decide to unlock it - so that the exposure is recalculated as you modify lights - uncheck this box. What ever setting you choose will be remembered the next time you use lighting channels.

In this first image I have locked the Luminance, then lowered the lights and turned self glow off in order to get a somewhat dim scene.

Then, leaving Luminance locked I added self glow to the back panels. This gave me the desied effect of increasing the intensity of the panels, and their reflection in the mirror, without compensating by lowering the intensity of other objects.

Enjoy! - But use with care.

Note: Locking only works properly after the first pass has rendered - since the initial value of Average Luminance needs to be calculated while rendering.

See also