That is a question I’ve been wondering about and speaking to several Law Enforcement about it because they tend to do a little more hard use of weapon mounted lights and, from what I’m told, there are rules amongst them to not have more than 2 people using flashlights when doing an entry. It’s a guy thing to want to accessorize the heck out of your AR15, but unless you might be using your Carbine in an outdoor situation, you absolutely should consider the fact that there is such a thing as too many lumens. I’ve been very happy with about a 6yr history of using a Streamlight Polytac on one of my LWRC M6A1 Carbines which only had 130 lumens and it suited me well. Now that LED technology has improved so much there aren’t very many flashlights below 200 lumens unless they have a high and low power setting. Personally, I’d like to see something like the TLR1 series of flashlights have some type of high and low power setting on them.
What kind of options are there for very simple and lightweight carbine lights? In my opinion it really comes down to the Streamlight TLR-1s which is a 300 lumen flashlight with strobe, the Streamlight TLR1 flashlights that is 630 High Lumens is the TLR1-HL, and the Streamlight TLR2 which like the TLR1 is 300 lumens, but is a laser light combo. For some reason we see a pattern of people using the TLR-HL light more on handguns than the TLR-1S. There is about 1HR and 25 minute run time difference between the two, but since your average Patrolman is more likely to have a sidearm on them and be outdoors the TLR-HL seems to be a better option, that could also apply to anyone that is CCWing and might be outdoors. I would find the 630 lumen output to be an overkill for indoor use. There is some good information on the Panteao Production Make Ready with Pat Rogers : Intro to the shoot house DVD where Pat, does some very good flashlight demonstrations in outdoor environments so check that out.