Nuts and bolts regarding dive lights

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Bobby

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This is from a thread that I responded to a question. It might be helpful for others so I posted it here where it is more easily found.

Lux is the measurement of the amount of light that reaches a specific distance and angle. The problem is that there is not a set criteria for the Lux measurement like there is for Lumen measurements. Just saying a measurement at 1 or 2 meters does not even begin to get a measurement that can be compared with another. A couple of millimeters distance difference or a degree of angle difference will throw the measurements of considerably. We haven't even began to discuss tuning and accuracy for the meter itself. Lux meters can be bought for around $100 US however their accuracy leaves a lot to be desired. The Lux meter we use is on the upper end of the cost side however delivers high end accuracy.

We have built a Lux "Box" that allows us to take accurate measurements of our and other lights. We don't publish these numbers because they are meaningless for comparison with other manufacturers. It allows us to check our products performance with a repeatable number that is useful to us internally. It is easy to boost the numbers we get by shaving a few millimeters off the length of the box to shorten the measurement distance or lower them by making the box a little longer. Repeatable numbers are what is useful to us internally.

We could build a Luminous Sphere for a little over $1500 US however our accuracy would not be close to what is required. To get the needed accuracy the starting point for a sphere is around $50K, which we definitely can't afford. So we use conservative LED manufacturers Lumen numbers, from a manufacturer calculation sheet, that allow us to plug in variables that are adjusted for how our lights are used. There are some manufacturers that inflate their numbers and/or use spec sheets that are more marketing material than real numbers, however most of the quality manufacturers today use conservative Lumen numbers. Again though, the best way to compare lights is to take them on a demo dive.

As I have always said the best way to know if a light fits your needs is to test dive it. That is why we encourage our dealers to have demo units, which almost all of them do. Optics play the biggest role in the beam angle and quality. You can have two lights with one putting out 1K Lumen and the other 2K Lumen that give the same Lux reading at a set distance due to the beams that their optics produce. The 1K would need to be focused down to a light saber type of beam with no peripheral light while the other beam would be wider and more dispersed. Even if all the manufacturers sent their lights out to be tested by an independent facility, to have direct comparison, it would only give a piece of the needed information. Our 10K Lumen video light puts out almost 3 times as much light as our highest output primary, however measures a lot less Lux due to the wide video beam. Having the right beam to fit the need is what is important. If you have a super tight beam with no peripheral light it is harder to see around you, a too wide or dispersed beam won't penetrate far enough. Having multiple power settings is helpful with varying conditions or dive requirements. There are a lot of factors, when discussing the beam, that are important in making a decision.

Now after talking so much about the light output and the beam, which is important, it is also important to keep in mind that it is not the only thing. Quality of parts and manufacture, innovation, reliability, warranty, and service are a few more things that are also equally as important, IMHO. If the light needs to be serviced or repaired where does it have to be sent? We have established repair facilities in Europe and Australia to support our customers outside the US. They have factory training to ensure that our standards are maintained. I believe that the difference in the details is what sets one company apart from another.

Bobby
 

lowviz

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Bobby,

I've gone through an old 75W OMS Phantom (I still dream about it) and an HID. Waiting for my second HID to die beyond repair. One of your lights is next. No clone or ripoff, one of yours.

I agree with everything you said in your OP. Furthermore, I see absolutely no intent (by you) to put a 'spin' on your position. Just the facts and an honest attempt to get it right. I dove one of your lights at Marianna. Loved it.

So, forget the sphere unless you can't trust the LED manufacturers. No point. It all comes down to your package, intensity, and beam angle. Suggestion: Get an old OMS Phantom (doesn't have to be working) to see how they accomplished user focus. It was beyond amazing. Burn time with lead-acid just didn't cut it though...

I'm no stranger to light measurement, this is my light meter. I know what beam angle I like so I just pick a reasonable working distance and take a measurement. Easy to compare.
Meter.JPG

Edit:
Looks like they kept the "Phantom" name for a much different offering. Confusing. The dive light that I am talking about is given in the pic below (that I stole from the internet).

OMS Phantom.jpg
 
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Bobby

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lowviz,
Thanks for the good words. Optics are really tied to the light source. We developed our optics for the LED's that we use so they are more or less tied to them. We believe we have the best balance between peripheral and penetration lighting. There are a number of older lights that really hit the sweet spot for their technology. The DR 24w HID is another that comes to mind. Really good beam balance IMHO. I may have one of the OMS phantom heads that you pictured in one of my old parts boxes. Before you ask I rather doubt I have all the pieces and parts to put it together if I even still have it. For our recent move I threw out two garbage cans of old light parts. I've been collecting bits for too many years and it all just gathers dust now. If I want to tinker I simply make up what I want rather than try to work it into an old head from another generation. :)
 

lowviz

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That light head doubled as a hammer! Not asking you to duplicate it.

My point is that you may be able to reclaim the off-axis light or maybe even defocus your LED's so that you can re-focus to get a wash or a spot by reflector focussing. No big deal, just a thought.

I love a light that can be focussed.

Disclaimer: Nothing like a wash light for quick and cheap video. :wink:
 

lowviz

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Old habit from when I used to shoot film. I'd take several pics at various beam angles. One would always be dead on.

A diffuser is fine but it is one more thing to fuss with and you only get a tight beam or a flood, nothing in between.
 

kelemvor

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I bet this is going to become an often referred to post. You might want to cross post or link to this over on candelpowerforums.com. It's an often debated topic and usually isn't so well articulated.

I tend to look for a lumens measurement precisely because of the problem in objectively comparing lux. Then I look at things like beam angle separately. I have to admit when shopping for lights, I often discounted products without a published lumen value. I think I would still do that if I were to buy another one today.

It would be a great world if dive gear (especially dive lights) could be used before purchase. More often than not, it cannot so you've got to compare in some other way as best you can. Even after purchase, most places won't accept gear returns if it's been wet. So buying and returning if it's not what you expected isn't an option either.

You've got a good reputation at UWLD, but aside from that, and without being able to try products in the water - it becomes a "trust me, my stuff is great" sales situation.
 

tbone1004

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To my knowledge, in the US, stocking dealers with demo units
Cave Adventurers, Dive Right in Scuba, North East Scuba Supply, Scuba Tiger, and I'm sure there are a handful of others. Not convenient to all obviously, but convenient to those where these lights are intended to be used. Cave Country, Great Lakes, etc. One of the nice things in the tech community at least is that most of us are quite willing to let guys try gear out. It is a rare occurrence that I get to a dive site and someone isn't asking about some sort of gear that I have and they take it for a test spin
 

lowviz

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...//... I tend to look for a lumens measurement precisely because of the problem in objectively comparing lux. Then I look at things like beam angle separately. ...
As you know, beam angle has everything to do with lumens. I have a laser pointer that will (by lumen specs) blow the socks off any dive light out there. Yes, a gross exaggeration but it makes a point for those who are less into lux and lumens.

...//... It would be a great world if dive gear (especially dive lights) could be used before purchase. ...
Next time you drive by Cave Adventurers...

...//... - it becomes a "trust me, my stuff is great" sales situation.
I see it as much more than that. You can talk to some companies and others couldn't care less about you want.

Look at Shearwater, a bunch of us here at SB made our opinions known as to how they implemented their electronic compass. Shearwater changed the programming in their Petrel 2 and made a lot of owners happy. IMHO, that really counts for something.

As for "trust me, my stuff is great" I'll sooner buy with regard to functionality. I don't mean that the gear needs to suffer from "functionitis" either. A million options that confuse the user is no benefit.

As to functionality, I'll give my opinion as to what I would like to buy. If you don't ask, they won't know:

At least an hour's worth of burn time on full intensity, focusable beam angle from pencil beam to full flood, continuing to turn the light's bezel past flood will engage an iris made of diffuser material. I'd save up and buy that. :)
 

kelemvor

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Well, customer service is a factor in my purchase decisions for sure. It's part of what attracted me to shearwater, and why I won't buy anything more from scubapro. Like I said I've heard nothing but good about UWLD.

My comments were mainly covering why I consider lumens an important value to know when evaluating any light before purchase. It's not the only factor to consider, as UWLD mentioned in the original post. I also said as much previously.

As you know, beam angle has everything to do with lumens. I have a laser pointer that will (by lumen specs) blow the socks off any dive light out there. Yes, a gross exaggeration but it makes a point for those who are less into lux and lumens.

Next time you drive by Cave Adventurers...
If I ever go dive jackson blue, I would definitely stop by.


It's just too bad there isn't some better third way to objectively measure light performance.
 
https://www.shearwater.com/products/teric/

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