If the cameras are on the inside, looking out, you'll possibly be stuffed ! IR has problems getting through windows ! In which case, 'white light' exterior security lights on a PIR sensor. (Dirt cheap, 10 quid in Argos? )
If the cameras are 'overt' exterior, then go for white light anyway, as they're a bigger deterrent than than the camera.
If the cameras are covert / 'discreet', or you just dont want to piss off the neighbours every time a cat goes past, go for the IR.
Most cheap 'commercial' IR Illuminators, are around 750-850nm, ie: they're not properly covert anyway, giving a dim red glow like a fag butt at 25m ! Covert ones are up around 950-980nm, which may be great,....BUT..most mainstream cameras are only around 5% efficient in that range, so you REALLY have to make sure that your cameras gonna be able to see 'em.
And, last of all, how far away is your area of interest ? IR Illuminators generally have lower range than 'white light'.