Pretty much a beginners question. Have been watching a few Builder type programmes (Holmes on Homes etc) they have battery drills which seem to have a light on the front I can see you would (might) need a light for screw head finding that sort of thing but these lights only seemed to be "on" when the drill was turning. Why have a light that is "on" only when the bit is turning?
Bad design? There's a laser line on my mitre saw which is similarly annoying and only comes on when the blade is actually turning - which seems a bit pointless (I'll get round to rewiring it with a switch at some point)
Many of the battery drills have a light that is wired to the trigger. On the better ones you can pull the trigger gently and turn the light on without starting the drill. It probably omits the capability to switch it on all the time since this would be easy to forget and a very effective way of flattening a battery to the point of damage.
Needless to say if you are working under film lights etc you probably don't require the light and just use the trigger just for the purposes of turning the drill, and hence create the impression that it is locked to operation of the drill even if that is not actually the case.
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