Interesting...I just became re-certifed as a GLOCK factory Armorer for the 5th time on Tuesday. This year our instructor, actually said while this light was at one time one of the best, I would suggest you look elsewhere as you'll find a much better light on the market. He said while he is suppose "to talk up" the company's products he couldn't do so in good conscious. He suggested we advise folks to go to Surefire, Streamlight or one of the other lights whose technology has kept up with the new developments.
The GLOCK light was state of the art 10 years ago and now it is not.
I'd call the folks at US Tactical Supply http://www.ustacticalsupply.com who are a DOD contractor and supply a ton of gear to the military and LEOs and ask them what they recommend. They carry several brands and they get a lot of feedback from their customers and besides many of them are former LEO/Military and still continue to train at the top name defensive firearms schools.
Speaking from experience (not that it really matters), I would steer away from conventional wisdom and the current trend and not go with an LED as a weapon mounted defensive light. While LED technology is the way of the future and state of the art, the LED technology and light spectrum is still not able to penetrate smoke, fog, mist, or gun-smoke like the old antiquated Incan lights. And brighter doesn't make it better. So I use a Streamlight TLR light on my entry handgun.
We've found through testing that brighter is not better for defensive lights. You don't need to find a flea on a mouses back. You need to find threats, and see what is in their hands. Brighter only backlights you more, and negatively affects your night sight as it bounces back from white/lite colored surfaces inside buildings and vehicles. Incan lights tend to penetrate deeper into the dark, and especially air with particulate matter such as dust.