"Dim lights" on scene

[Jeff]

You could try fading a quad placed on the screen:

import viz
viz.go()

viz.add('gallery.osgb')

blackScreen = viz.addTexQuad(parent=viz.SCREEN,scale=[100.0]*3,color=viz.BLACK)
blackScreen.alpha(0.0)

vizact.onkeydown(' ',blackScreen.runAction,vizact.fadeTo(0.7,time=2.0))

Also take a look at the post process section in the Vizard help. Post process effects are applied to the whole window. You can experiment with built-in effects using the PostProcess.py example script( File -> Quick Open: type 'PostProcess')