The thing is built like a tank and the light and battery housing have Oring seals to keep the water out. However as soon as water touches the LEDs they turn on about as bright as a cigarette cherry, perhaps a little brighter. Something to keep in mind... under water its even worse. Also you cant get the water proofed version. I waited 6 months for one I had on order before Surefire said they would not realease it to the public. I gave the standard M900 a dunk in the sink for ten minutes and the result? The bezel, lamp housing had ZERO water and functioned perfectly, the battery compartment had ZERO water and functioned perfectly. The whole unit and every switch worked PERFECTLY and even did so while still underwater. The LEDs were still on after removal from water (they are brighter while actually filled with water than just wet) but the kill switch on the grip killed the LED glowing as well as the whole light. So they can be turned off by cutting power but they you have one EXPENSIVE front grip with no lights. [:(]
The glowing contiues for a long time. I never checked to see how long before so I have just rewetted it and will give a time till the LEDs go back to normal.
Well its been just over an hour and its not as bright as a cigarette but its still on... about half as bright, and I am getting sleepy.