@FernadoK, load your level you want the ambient light changed and then select File-->Build Game.
Click on the Level Settings tab and click EDIT on the line that says Global Script.
Scroll till you see the ambient settings and modify to how you want them to be. Below shows it being switched off completely.
Click ok then OK, then OK on the build game dialog and when you test the game again the ambient settings will have changed.
I haven't tried experementing with screen sizes at the moment.
Jas
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"What is this talk of 'release'? Klingons do not'release' software. It escapes leaving a bloody trail of developers and quality assurance people in its wake!"