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Primary Light for cave diving?

Discussion in 'Cave Diving' started by CAPTAIN SINBAD, Jun 13, 2019.


    CAPTAIN SINBAD Divemaster Candidate

    # of Dives: 200 - 499
    Location: Woodbridge VA
  2. EireDiver606

    EireDiver606 DIR Practitioner

    Lumens don’t give the diver anything useful to work with. Most claimed lumens ratings are just that. “claims”. They start off at the lumens maybe and very very quickly drop or else they’re simply lying completely. Lux is the real measurement. After hearing @tbone1004 I understood it more, he will be able to help you out here.

    Hey @kensuf how do you like your Focus 2? Is it worth the big bucks?
    rjack321 likes this.
  3. Brian G

    Brian G Nassau Grouper

    # of Dives: 100 - 199
    Location: Pittsburgh
    Doing some math on the 15000 lumen claim, I see 7 x 18650 batteries lasting for a claimed 2 hours on high. If we assume the highest capacity 18650 batteries (3.5 amp hour) and a very generous average voltage (3.6 volts), then the total available watt hours is 7 batteries x 3.5 amp hours x 3.6 volts = 88.2 watt hours. If the battery life is two hours, then that comes out to 44.1 watts. The XML-2 leds they claim to use have a MAXIMUM efficiency of 170 lumens/watt. So at the very most optimistic estimate, it will be 44.1 watts x 170 lumens/watt =~ 7500 lumens. Max. Curiously almost exactly half of claimed. Note that I seriously doubt that the leds are being run at their most efficient power point, but at least with 32 leds they are not claiming that every led is putting out the max output, which several companies do.
  4. tbone1004

    tbone1004 ScubaBoard Supporter ScubaBoard Supporter

    # of Dives: I'm a Fish!
    Location: Greenville, South Carolina, United States
    @Brian G and that math holds true for almost all of the BB lights. The average lumen across the total burn time is about half of the claimed lumens. It starts off brighter than that, usually around 3/4 of the claimed lumens but falls off quick. It's fine if you're an educated consumer and treat the lights for what they are, but most people are not which IMO falls under false advertising claims. I much prefer constant output drivers personally. A lot less burn time, but more useful and consistent light.
    wKkaY and Brian G like this.
  5. Reku

    Reku Solo Diver

    # of Dives: 5,000 - ∞
    Location: Great Lakes + Northern Florida + Marsh Harbor
    I use an uwld35 - it works well. I run it on medium or low.
  6. _Ralph

    _Ralph Manta Ray

    Another fan of the focus 2.0

  7. wetb4igetinthewater

    wetb4igetinthewater Instructor, Scuba

    # of Dives: 500 - 999
    Location: Seattle
    There was a recall for the Big Blue canister lights (I had one and turned it in) and Big Blue no longer sells any such lights.
    crcobb likes this.
  8. JohnnyC

    JohnnyC PADI Pro

    # of Dives: I'm a Fish!
    Location: United States
    That's a video light. That's not a primary light. You're gonna have to fling that thing around like a meth-addled cat to even come close to signaling with it. And it's useless with particulate in the water.
    rjack321 likes this.
  9. tursiops

    tursiops Marine Scientist and Master Instructor ScubaBoard Supporter

    # of Dives: 2,500 - 4,999
    Location: U.S. East Coast
    That is a video light. You do not want that in a cave as your primary...can't signal with it, and too often in someone else's eyes.

    There is an echo in here.....
  10. helodriver87

    helodriver87 DIR Practitioner

    # of Dives: 500 - 999
    Location: Alabama
    For my money, you can't go wrong with Light Monkey or Halcyon. I use a LM 32W VF LED as my primary. It's fantastic in clear water. Head and shoulders above the Focus. That thing lights up a cave better than anything else I've ever used. But when I get into darker water or places with lots of particulate, I find myself a bit jealous of my buddy's Focus 2.0. The "punch" is significantly better. Ideally, I'd own both. It's just not high on the list of priorities right now. But you can't go wrong with either. Build quality and service after sale are top notch with both.

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