I have to beg to differ about ambient lighting, it's not like turning your monitor brighter. It is an overall actual amount of light in your scene. It will wash out shadows, take depth out of textures and reduce the contrast of your render. I haven't really found a good use for it except in quick test renders to see placement of objects better. I never use it in a final render. If you want back lighting, put in a key light and use a complementary color to your main light. I constantly see 3D renders where the main light source is white light. This almost never happens unless you're in a bathroom or something. If you want to add depth and richness to your scenes, use a little clor in your lighting. Also, with HDRI or GI specifically, ambient light is really unnecessary because you are already filling in your backlighting by bouncing off the surrounding surfaces. The default setting of 20 for ambient is quite high in my opinion. Study some of the scene wizard lighting setups to see some good basic examples of ways to light scenes. The proper lighting can really enhance a mediocre model, while poor lighting can ruin a great model. Just my opinion, I could be wrong.... Patrick Tuten