Subject: How much light does a human eye need to see an object clearly at 12m?

Situation:  A police officer enters a completely dark room with only 
a flashlight as a source of light.  There is a person standing 30 
feet or 12m away with something in his hand.  How much light must be 
produced by the officer's flashlight for the officer to accurately 
identify the object ?   We can assume that the object is a common 
one, and that the officer has 20/20 vision.  I think this question 
touches on perhaps biology and physics, but I could only pick one 
topic.  I would be happy to clarify if needed.  This is a realistic 
situation, but does not pertain to any specific event which as 
occurred.

Re: How much light does a human eye need to see an object clearly at 12m?