Replacement Lenses: Output Comparisons

I got around to trying out a bunch of replacement lenses in my "Lightbox apparatus" with a 4-D Mag. There are the results.

No Lens ---- 4000 (Baseline)
UCL Lens --- 3980
UCL LDF ---- 3950
Stock ------ 3800
Acrylite --- 3650
Writeright - 3650

So there you have it! This was a measure of the overall output from the 4-D with the various lenses in place, focused to the tightest point.

With my apparatus the UCL shows about a 5% improvement over the stock lens.

The UCL-LDF, although it diffuses the heck out of the beam, still lets almost all of the light get through!

The Acrylite and WriteRight perform about the same for overall light output through the lens.

The stock lens cuts out about 7% of the light coming from the reflector! Ouch!

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Quickbeam said:
I got around to trying out a bunch of replacement lenses in my "Lightbox apparatus" with a 4-D Mag. There are the results.

No Lens ---- 4000 (Baseline)
UCL Lens --- 3980
UCL LDF ---- 3950
Stock ------ 3800
Acrylite --- 3650
Writeright - 3650



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Doug
A comment on lab technique for this type of measurement. Where we are attempting to determine the small differences among different lenses, it is important that the light source be stable. For an unregulated light such as this, small voltage changes make significant changes in output. Fresh batteries would be worse as they drop steeply during the early part of the discharge. This could be best controlled by using partly discharged NiCds so that you are operating in the flat part of their discharge curve. Another problem is the variability of the contact resistance of the switch. The later could at least be checked by turning the light on and off and seeing the range of variability of the measurement.

I took all the measurements once, then took them all again. Removing and replacing the lenses and refocusing the light each time. The readings were quite stable. The light was on for less than 5 seconds per reading.

This isn't anywhere near lab-grade equipment, so I'm not even going to pretend that hyper-accurate techniques are required/needed. The readings did verify themselves as stated above when two separate readings were taken in two separate trials. That's good enough for me. /ubbthreads/images/graemlins/smile.gif

Anyone dissatisfied with the results can certainly do their own tests. These are the results I got with my equipment. YMMV.

BTW, they weren't tested in the order you see above - I placed them in the order of diminishing output, so the drop in numbers in the list was not due to battery depletion.

Thanks for this information. I am rather surprised that the glass diffusion lens let as much light pass as it did.I would have expected it to cut the light output somewhat more.

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Quickbeam said:

. . . The stock lens cuts out about 7% of the light coming from the reflector! Ouch!

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A few months ago I measured reflected light from the ceiling and found that the stock lens lowered the light intensity by 9 per cent. A little more ouch. /ubbthreads/images/graemlins/smile.gif

Quickbeam, thanks for posting these numbers. It's nice to see that the LDF on the UCL does not significantly degrade the light output.

Paul

All I wish to add to the discussion at this time is:

In MY experience in using Writeright and Acrylite (of which one or the other is absolutely NEEDED with a M*g!) I find Acrylite to do a noticeably better job of fixing a beam than Writeright!

Sure, using either one cuts some output. But as someone has as a tagline: There is nothing in the world as bothersome as a rotten beam. (or something to that effect!)

Quickbeam, this is very interesting to me. I replaced the stock lens on my Mag 3D with a UCL from Flashlightlens.com last spring and it seemed to be brighter, but I didn't know how much of that was just having a new, unscratched lens.

Do I understand correctly that, in your tests, the UCL passes 99.50% of the <font color="red"> QUPS </font> that get measured with no lens? So, one-half percent of the light-thingies (I'll be glad when that contest is finished) are....uh, hmmm...sumpin happens to 'em? /ubbthreads/images/graemlins/thinking.gif

Comparing my new G2 with FLL's UCL, side by side with a friend's stock G2, (both with brand new SF-123s) the difference is evident. Simply subjectively speaking of course. /ubbthreads/images/graemlins/grin.gif

Thanks for doing this. /ubbthreads/images/graemlins/thumbsup.gif

BC

[ QUOTE ]
Do I understand correctly that, in your tests, the UCL passes 99.50% of the light-thingies that get measured with no lens? So, one-half percent of the light-thingies (I'll be glad when that contest is finished) are....uh, hmmm...sumpin happens to 'em?

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Yup. Sumpin' happens to 'em! They're absorbed by the lens material and re-emitted as heat.

I was really surprised by the numbers, especiall the UCL-LDF - I was expecting a lot more light loss in the lens, but only about another 0.5% is lost to the coating (according to my non-calibrated, non-standardized, potentially wildly inaccurate set-up /ubbthreads/images/graemlins/wink.gif ).

I may have an idea of why the LDF passes so much more light than expected...

I'm pretty sure the LDF spreads the beam a little more than the acrylite, but the difference lies in the substrate. The LDF film is placed on the top of a UCL lens. Being that the UCL passes at least 99%, and the LDF film is a mere .007" (plus a few thousandths for the PSA) thick, this should allow a pretty good amount of the original source light through. Because of its thickness, the LDF film may account for around a percent or two loss (numbers above show less than 1%). The numbers above tell me that the light transmittance of straight acrylite is somewhere near that of polycarbonate. The diffusion characteristics of the acrylite texture would make that number look a little smaller due to the reduction of hot spots.

I'm not too familiar with acrylite (I need to buy a few lenses).

Does anyone else agree with this theory?

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flashlightlens.com said:
I may have an idea of why the LDF passes so much more light than expected...

I'm pretty sure the LDF spreads the beam a little more than the acrylite, but the difference lies in the substrate. The LDF film is placed on the top of a UCL lens. Being that the UCL passes at least 99%, and the LDF film is a mere .007" (plus a few thousandths for the PSA) thick, this should allow a pretty good amount of the original source light through. Because of its thickness, the LDF film may account for around a percent or two loss (numbers above show less than 1%).

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Chris,

I think that you likely have correctly identified beam angle errors as the source of the unexpected performance of the UCL with LDF. Doug has already stated that he has seen variations on the order of +/-5% [i.e., a range of 10%] due to beam angle alone. Since the UCL with LDF reads higher than expected, it appears that the Moo-box has a positive bias [relative to narrow beams] for beams spread to the extent that your LDF does. As soon as I read Doug's post here, I went to your site to order a UCL with LDF to see if I could replicate Doug's data. I do not know who supplies your LDF or it's beam angle, but looking at the spec sheet I have for the POC equivalent material we should have seen a reduction of 10-15% depending upon beam angle. BTW, I sent you an email asking about the supplier and beam angle of your LDF. You can answer in this thread instead if you choose.

Thanks Quick! Very interesting thread.