What do you consider enough lumens?

[rushca01]

I posted a response to a thread on another forum (hint..rymes with barf) to the question in the title.

I responded with a good rule of thumb is:
2 lumens per yard to IDENTIFY
1 lumen per yard to OBSERVE

Example: 120 lumens would give you aprox 60 yards to identify a target and be able to engage that target with cerntainty and aprox 120 yards of light to observe a target only.

This was the rule of thumb given to me at a low light/no light class taught by LMS Defense.

One of the responses I got was...that I was an idiot and didn't know what I was talking about. I brushed it off and didn't even respond as I trust my source.

So what say you, what do you consider enough lumens?

ETA: Assuming these are tactical weapon mounted lights. I assume most tactical oriented lights are going to have similar beam profiles given their intended use.