I'm sorry, for the sake of newbies, I have to add this since there are so many products out there associated with it...

"Global Lighting" is just another renderosity faker...and I am talking about any kind of lighting which involves the obligatory 800-lights-on-a-sphere-all-set-to-level 2 routine. The low levels of light are meant to simulate the bounce of light from other sources, like walls, oceans, etc.

Sooo...if you're using AO or IBL or renderosity calculations...YOU'RE NOT SUPPOSED TO NEED GLOBAL LIGHTING AT THE SAME TIME. Supposedly, the other mechanisms will replace it.

(Offered just cuz you're not going to find this stuff explained anywhere else...)

Your software may have "Global Lighting" (also known as "Global Illumination") built in. These are usual renderosity calculators - and may involve additonal routines for the artist-creator to help the software identify more-and-less reflective materials to take into consideration when calculating renderosity.

Renderosity calculation is complex. Faking renderosity is sooooooooo much quicker and easier. Which is also its downfall. Misapplied IBL or AO is no more realistic or effective than any other badly managed lighting or other artistic technique - just using them is not a guarantee of a better result. In fact, it's more difficult to create dramatic scenes while faking reality than it is to just light it the way you want it.

That bears repeating. IT'S MORE DIFFICULT TO CREATE DRAMATIC SCENES WHILE FAKING REALITY THAN IT IS TO JUST LIGHT IT THE WAY YOU WANT IT.

It used to be said about college that diplomas are nailed to the wall not grades - i.e. the result is more important than the mechanism. I don't think that's always true in RL....but I do believe it's always true in the pictorials arts. We don't see how ya got there...we only see the 'there." So if you need to add some ambience to a material which wouldn't normally have ambience... or fake renderosity by adding a totally unrealistic light somewhere ... or by doing some grotesque manipulation in post...DO IT. Unless you're a scientist studying this stuff. But if you 're an artist, do what you need to get your result - no other artist is going to think less of  you for it.