Choosing a DIR-compatible light, probably canister, tight beam, mostly for PNW diving

[MikeRD03]

To use Bobby's example, 4000lm light with 120* angle is equivalent in penetrating power and intensity as a 2000lm light with a 60*angle

I am sorry, but you and Bobby are wrong. The surface is a squared number, so equivalent brighness/penetration of a 4000 Lumen/120° light would be 2000 Lumen with 102° and not 60°! Or said other wise - for double angle you need four times more light! (2²) The reason why video light are Lumen monsters.

And lux is always measured where the light comes out of the lighthead at 1m. So no problem here. But many light makers are lacking of this important number, so you should ask for it and don't let yourself fouled by accepting sayings like Lux ist not important. ;-)

Of course numbers can not describe the light distribution of a torch, but comparing Lux, Lumen (real) and full angle (50% brightness to 50% brightness) you have an idea in what direction a light is going. But most lights a lacking of all or at least one of these numbers.

 

[decompression]

Mike is now my "go to guy" for anything light related............I used to check my primary with my back up to see it the batteries were dead...[emoji2]


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[lucca brassi]

To use Bobby's example, 4000lm light with 120* angle is equivalent in penetrating power and intensity as a 2000lm light with a 60*angle

that mean even light without hotspot


4000 lm /120°/5 m distance = 50,93 lux

2000 lm /60°/5m distance =95,4 lux



4000 lm /120°/1 m distance = 1273.24 lux

2000 lm /60°/1m distance =2375.9 lux

 

[Bobby]

OK folks it seems I have been brought up a few times here & some of what I have said has been lost in translation. Lux is an important number when looking at the performance of a dive light (or any number for that matter). The issue with using Lux numbers is that there is not an industry standard. Yes 1m is an accepted measurement however there is a lot more that goes into getting an accurate Lux measurement that could be used for comparison between different manufacturers. A slight change in distance or angle will make a big difference in the Lux reading.

We have made a custom Lux box for checking our lights actual output as well as other manufacturers. The reason that we don't publish the numbers is because many manufacturers inflate Lumen numbers a good bit and it is even easier to make crazy Lux numbers. Years ago I spoke with people about Lux and it seemed only to confuse the issue. What I have said is that we use conservative Lumen numbers from the manufacturers to offer a level way of comparing light output. I have always recommended that folks dive our or any other light as the best way to know if it is the light for them.

It is also accurate saying that the expense for accurate Lumen measurement is vastly more expensive compared to the investment for Lux measurement. Just to have something that would be capable of taking reliable numbers for dive lights the investment for Lumen is around $50K USD. There are cheaper ways to do it however the accuracy is not possible. Lux has its own issues as well. An inexpensive Lux meter will be rather inaccurate and give a fairly wide range of readings even on lights that are putting out the same Lumen with the same optics. Our Lux meter is rather expensive and close to the top of the range in accuracy. Until there is a standard for accuracy for the meter and how the measurement is taken to control distance and angle Lux numbers, IMHO, only help confuse the issue. For those that really want it our LD-35, on our Lux box, puts out 110,000 Lux. That is at a distance of 1m with the beam angle controlled.

 

[MikeRD03]

I've heared it a lot of times, that numbers like lux and lumen are not published, cause they confuse customers. Well, it should be up to the customers to make the decision if they are useful or not. And if worried there are some fine forums like this one to clear things up. ;-) Btw, there are professional light measurement service provider out there, so no need to buy expensive equipment in case someone is interested to publish real world numbers. I use them on my own, too.

Regarding your LD-35 I have to admit I've never seen any Light Dude light here in Germany, so I never tested one before. (I do tests for my own interest and write articles for the German diving press) Based on my experiences I would expect from a presumed tripple XM-L light with a 50mm head and 2000 real Lumen output with something around 30.000 lux@1m. I don't know how and in what kind of box(?) you are testing, but, sorry Bobby, 110.000lux sounds way beyond physics. ;-)

 

[Bobby]

Mike,
Thanks you made my point rather clear with your post. If we believed that using Lux numbers would help we would. As I said earlier we believe that the best way to determine if ours or any other light is the best fit is to go dive it and look at what features come at what price point. Even though our Lumen output is higher than the numbers you used the point is that Lux numbers will vary considerably due to the lack of a standard. Please keep in mind that the only reason I came into this thread is because some of the things I have said were a little out of context. None of it was purposeful, I simply wanted to clarify.

BTW I grabbed an LD-35 off the shelf and took a quick Lux reading.

 

[eelnoraa]

Boddy, I wonder what would be a typical 21W HID lux value and lumen? how about your LD26? I recently dove with 21W HID and LD26 side by side. I notice a significant difference in beam characterstic. Before I say my observation, I want to see if the measured number matches my experience.

 

[Bobby]

*Note* I'm not bashing any manufacturer in the following post. I'm answering a question and giving an honest answer and only talking about types of lighting and not any manufacturers.

Elnorra,
I have a note book with measurements that we took when we put our first prototypes together and were testing them with other common lights on the market. Unfortunately we moved recently and I don't know where it is located so the best I can do is from memory. We used new HID lights with new ballasts and bulbs because of the rate of deterioration in light output for HID. Our LD-26 model was putting out the same numbers in Lux as a 35w HID. When we did in water comparisons we had both a 21w & 35w HID with us. The person doing the testing with me that day, which was a die hard HID fan BTW, decided to drop the 21w out of the mix rather quickly. We continued comparing the 35w HID and the LD-26 for over an hour. As far as numbers IIRC the LD-26, on our Lux box, was in the 75K range and as I said it was dead even with the 35w HID. The LD-15 from memory was about 20% higher than a 21w HID in Lux. In our comparison video, again IMHO, it is easy to see that the LD-15 puts out considerably more light than a 21w HID and even does a fair job when compared with a 35w HID.

We made every effort to get accurate data because this testing was what determined if we were going to manufacture our dive lights. We adjusted the focus on the HID's to ensure that while taking the reading we were getting the most concentrated beam from them. We took the time & measured the light output to allow the HID's to warm up to full temperature. We used new bulbs and ballasts & even had to switch out a few to ensure that they were operating optimally. Bottom line is that we made our best effort to get accurate data to make a valid decision regarding entering the market with our own products. Nothing has changed from that day in how we look at or talk about things.

 

[MikeRD03]

Hey Bobby, I don't doubt your Luxmeter is showing this number, but I think you're measuring it an odd way. ;-)
And I am wondering why you're measuring lux "in a box"? I do it in a wide room in order to reduce false metering from reflections.

btw, your web site here: http://uwlightdude.com/lumens-lux/ shows a clear misunderstanding of the relation between lux and lumen. When taken example 1 with 30° the brightness in example 2 is not doubled, in fact it is four times! Check one of the Lumen calculators in the web to verify and let me know ;-)

 

[Bobby]

Mike,
Thanks for letting me know about the error on our website. We have been very busy with the release of our new generation lights & a complete over haul of our website as well as running the day to day business. It is a simple mistake & not a lack of understanding, we will get it fixed.

The box is a simple design. It absorbs & keeps outside light from affecting the measurement while ensuring that the exact distance & angle is maintained. There are other published Lux numbers around that agree that our numbers are in line. I worked in the corporate lighting industry & do have some experience. No need to keep beating this back & forth, I simply wanted to clarify statements that were quoted in my name.

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