Ive been targeting the wrong fish.
Brinyte Div series would be good for well over 10 feet dunking (150 metres I think they are claimed to be rated for), decent price and review of other products have been good. I own a couple of their lights and they are decent for the money, I got mine very cheap. The pole is something youre going to need to sort though as it doesnt come with one, but a handle does screw on so a pole could be an easy fit. They have handheld dive lights and a canister light which is just the head, attached to a canister by a lead. Canister might be he easiest of them to use, and with 3 x 26650 its run time shouldnt be an issue with the right batteries. But, I have no idea about spread, and how much spread you need for fishing Flounder though.
http://www.brinyte.com/product/1397467939.html … not sure where to buy though. I went direct but they prefer to sell to dealers direct but will send a single if they think youre just sampling the product for a business decision. 0:)
EDIT: theres a Div10 triple or quad (not sure which) canister light too. Gets more expensive though.
Definitely look around on prices though, Ive fouind the Div 10 from $220 with batteries and a charger at http://www.aliexpress.com/store/product/diving-spot-light-canister-cave-diving-flashlight-3800lumen-DIV10-with-charger-and-battery-free-shipping/135872_32221781845.html#! to $340USfor what looks liek same package at http://www.dhgate.com/product/brinyte-div10-3000lumen-canister-light-with/237833933.html
review of Div10 linked from this forum by MRTdiver here Canister Lights - some budget can. lights , to another forum… http://www.scubaboard.com/forums/lights/491554-brinyte-div10-3000-lumen-canister-light-review.html