Hi David, and welcome to the forum! :welcome: Cave documentaries get me really exited! You'll have to forgive my long-winded half-off-topic response.
The quick answer is that as long as you put a high quality (powerful, high capacity) battery in it, the H602w will have no trouble running in 'high' for 45+ minutes. And, if the thermal stepdown does kick in (which might be unlikely in a cool damp cave) it will be subtle enough that you likely won't even notice it - perhaps dimming itself down to between 750-900 lumens or so but never any lower than is necessary to maintain a safe internal temperature.
I would just leave it at that, but you mentioned big rooms and deep pits and buying four identical lamps... here's where I might start to go off topic (sorry). :tinfoil:
Even if you buy four
or more H602w lamps they will
not effectively illuminate a really big cave chamber or deep pit - the H602 is simply not designed to throw its light very far outwards.
High
luminous flux in a wide-angled beam with no
collimation will still produce a relatively low
luminous intensity and thus the
illuminance it can produce at a given distance will be relatively low as well, dropping down below usefulness very quickly as it's moved away from your subject. If you are not at least somewhat familiar with the intricacies of photometry and how it applies to flashlight beams as well as lighting design theory for film and video, you're probably going to want to do some research before you buy a handful of expensive lights.
As a fellow cave documentary film maker, I can tell you that a few bare-diode wide-angle lights like the H602w will be an essential part of your subterranean video lighting kit - but you'll need lights that can throw further as well (and they might be quite a bit harder to source if you want them to project smooth clean light). The standard
hotspot+spill configuration produced by cone-shaped or parabolic reflectors is usually not ideal for video by itself, often suffering from ugly uneven beams where you need smooth lighting without noticeable overlapping, shadows, borders, or color aberrations. I hate to say this, but you should be prepared to do a whole lot of experimenting and trial-and-error... if possible;
before you bring your cameras underground. Lighting complex 3D spaces with multiple subjects at different distances is
hard, and caver film-makers don't enjoy the usual toolbox that caver still-photographers have (long exposures, multiple exposures, light painting, etc.) and as often as not we're moving the camera around through the scene too. In a cave the usual three-point lighting techniques that are taught for flat-backdrop studio applications will quickly turn into six- and eight-point lighting arrangements, with those various different lighting stations requiring different beam shapes/angles.
These hideous pics of my dingy apartment hallway and bathroom were taken with a Panasonic HDC-TM700K camcorder with every setting on 'auto' - that means it's not about showing overall brightness as our eyes see it, but relative contrasts like a video camera sees it. Crude lux meter readings provided by my GS3 cellphone's light sensor -that's the important part assuming you know what the numbers mean. Distance to bathroom doorway is approximately twelve feet. Both lights are in their second brightest mode (their brightest "H2" option).
First pic is of H602w @620 lumens - light meter reading at the bathroom doorway: only
11 lux. The camera (known for good low light performance and a decent
dynamic range) is trying hard but you'll notice that we still can't really tell what color the soap dispenser on the sink is. No problem lighting up both the door lock and the poster on the opposite wall though! Minor off-color ring around only the very outer boundaries of the beam. For everything BUT distance viewing, this arrangement seems ideal. The whole frame is lit, but anything out past twelve feet is almost too dim for the camera to render while the near-field is almost washed out.
Second pic is of an older dimmer version (MK I?) of the H600w @ 360 lumens - light meter reading from the bathroom doorway: a whopping 106 lux. That's roughly ten times the luminance from only half the lumens! Soap dispenser is now clearly green in color. Unfortunately there is an ugly boarder between hotspot and spill, the angle is too tight to illuminate both the poster and the door lock, and there are noticeable color variations along the beam which wreak havoc with the white-balancing and end up looking pink on my off-white wall (it wouldn't be quite as bad on a non-white rock surface, but it still won't look quite right). For closeup filming, a collimated beam can be ruinous with its uneven beam, but for distance viewing some form of collimation is essential.
Perhaps you can find some (potentially cheaper) lights that would be smoother and cleaner while still throwing a sufficient distance. Maybe instead of the H600w style textured reflector; an unfocussed aspheric lens, or a slightly-frosted TIR optic, or just try sticking some subtle diffusion film overtop. Sometimes I find myself combining a light with one optical arrangement with another utilizing a different setup, both pointing at the same subject from the same location, and playing with their respective outputs. That's the sort of experimenting you'll need to do. You might find that the optics that help the most next to a helmet-camera are not the same as the optics that work best set around a scene as part of a multi-point arrangement. I don't use my beloved Zebralights for videos any more because I've concluded that they make everything look flat and dull compared to other lights I've built (or commissioned other forum members to build for me) using other brands of less-efficient and less-bright but more-accurate diodes.
I think that an H602w will serve you quite well - it just won't serve every purpose and if you bought four of them for video use but had no matching collimated options you would be quite disappointed.
Further conversations about video lighting (separate from questions about certain models of headlamps) might be better suited for our "The Dark Room" photo/video section here, but I couldn't resist offering some additional application-specific details. You may have already known much or all of what I said, but I didn't want you buying a set of "mule" style lights and then wondering why they seemed way dimmer than everyone else's lights when it came time to film a deep pit or massive room. We'd love it if you shared the techniques and equipment you end up utilizing with us (over in the aforementioned darkroom section of course). Good luck assembling your kit, and stay safe down there! :thumbsup:
