well i've seen it turn off on some computers, but I have never been able to get mine to turn off completely under dim lighting conditions. Apple didn't bother to get drivers right somehow and a on some of the laptops, the backlight just doesn't turn off completely, whereas it does on some others (I've seen it turn off completely on some of the older Santa Rosa models, but it doesn't turn off completely on my early 2008 MBP.)