I'm also looking at weapon lights. Hopefully TZAX will find value in my Q+A.
I forget if the light I have is a Surefire or a Streamlight. It was about $50 a few years back. It has served me well .I put it in a 1 in QD scope ring that I already had. Its 200 lumen. With that light, I can see the mil-dot on a 100 yd sight in target in darkness at 100 yds. I also have a little flat Lazerlyte red lazer tucked under under the scope bell. That worked out,too. It had to do with a dead cow and night coyotes,not SD.
IMO,a good 200 lumen light would be adequate to know what you are shooting at to 100 yds.
However,for SD purposes,I have another question.I don't know the answer.
For SD,my light gives my threat something to aim at. My unproven theory is maybe if I have 500 or 800 or 1000 lumens,the bad guys eyes would be overwhelmed looking into the light. He might be able to point in my general direction,but hopefully,not see sights.
Reasonable plan?