Ambient light is a rendering term. It is a constant light that is added to the rendering. Renderes, like IRender, adds Ambient Light to a scene to represent more realistic lighting effect without having to enter every actual light source. Ambient Light is light applied to the entire scene. Using Ambient Light, you can highlight parts of an image with an actual light, and use Ambient Light to provide a flat, but usable illumination for the rest of the scene.
Decreasing the amount of ambient light generally produces images with more contrast. Too much ambient light can make a rendered image seem flat and uninteresting; too little can cause excessive contrast.
IRender nXt also uses Indirect Lighting which calculates the effect of light bouncing off of surfaces and illuminating other surfaces. This reduces the need for Ambient Light.
Note: I know everybody wants an "easy button" which will just make the scene look the way you want. But you will need to adjust some things to get lighting right. Be sure to use the Brightness Slider and Tone Operator to adjust the brightness of the rendered image.
Brightness slider on render window
Ambient Light Presets
Ambient light levels are automatically set with each of the preset, default, lighting types on the Presets Tab.
These levels can be overridden on the Presets Tab
The balance between ambient light and sun or artificial lights can adjusted on the Light Tab.
Ambient Light Balance
You can use the slider on the Light Setup Tab to adjust the balance between lamps and Ambient Light. Default 50%
Default Interior Ambient Light Balance
Balance at 90% - mostly sun, sky and lamps
90% Ambient Light Balance - mostly sun, sky and lamps.
Balance at 10% - mostly ambient
10% Ambient Light Balance - mostly ambient.
This is a 6-sided cube viewed from the inside. There are no lights. Why is the ceiling brighter than the floor? ( I get the same result with earlier versions, and without textures on the walls.)
The ambient lighting is intentionally non-uniform -- more light is directed upward.