Stupid experiment does this measure anything?

Let's say you have a flashlight and some paper sheets, if you cover the light with "n" sheets then you will see a spot in the top sheet, you can keep doing this until no spot at all is noticeable in the top sheet. Is the number of sheets of paper that you need a measure of anything? Because -don't ask why- I was doing this experiment and found some puzzling results.

Luigi

Whatever you do, do not try this with the USL.

NotEnoughLight said:

Whatever you do, do not try this with the USL.

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:laughing: :laughing:

Oh lordy did I ever need that laugh today!

:naughty:

If you can figure out how much light is lost for each piece, the it may be usefull.

but you'd need the paper layers to be of uniform thickness, which they aren't.
repeat the experiment, randomly sorting the sheets of paper.
repeat with different lights


... never mind. What is it that you want to accomplish? Then you can decide which experimental design is suitable.

and what are these puzzling effects you talk about? Your observations may be a function of your setup.

There may be variability of opacity within each individual sheet, too. (i.e. you could possibly shine the light through two different areas of the same sheet of paper and observe different degrees of light transmission, due to variable thickness, local variance of density of the fibers, presence of dyes or other photo-opaque substances, etc.)

If you're using toilet (toliet?) paper, Craig Johnson might be interested in using your testing methodology.

NotEnoughLight said:

Whatever you do, do not try this with the USL.

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What is USL?? Tell me, Tell me, I want to get the joke too

Ultimate Stealth Light

Links to threads here:

Ultimate Stealth Light thread index

Check out the USL Field Test threads. There are some nice pictures of the USL being used to set fires and cook eggs.

Well let's say I have the sheets numbered from 1 to N and I always place them in the same order one in top of the other and I have a "circle" marked where the light will be placed. If one light is neutralized with 24 sheets of paper while other takes 42 what does this mean?

Luigi.

Hookd_On_Photons said:

There may be variability of opacity within each individual sheet, too. (i.e. you could possibly shine the light through two different areas of the same sheet of paper and observe different degrees of light transmission, due to variable thickness, local variance of density of the fibers, presence of dyes or other photo-opaque substances, etc.)

If you're using toilet (toliet?) paper, Craig Johnson might be interested in using your testing methodology.

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If you use some reasonable paper this should not be a problem. Pick up a pack of premium 98 brightness paper.

luigi said:

I was doing this experiment and found some puzzling results.

Luigi

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Please share with us!

luigi said:

Well let's say I have the sheets numbered from 1 to N and I always place them in the same order one in top of the other and I have a "circle" marked where the light will be placed. If one light is neutralized with 24 sheets of paper while other takes 42 what does this mean?

Luigi.

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Assuming the pages were all essentially the same and placed on the light in the same way (I suspect spaces between pages would have an effect so smash them down) then you would have a measure, repeatable by you, that would measure light penetration.
This probably relates in some way to the lumens. But the lens diameter and focusing might have to be all the same.

Since it would be hard to duplicate with another set of paper it would probably be useful only to you and as pointed out only good for lights that did not set the paper on fire (or degrade it in any way)

Yes, assuming the conditions are always the same the idea is to compare different lights not to get a measure of something.

I started with a E2E it needed 42 sheets of paper to dissapear completely.
Then I grabbed a HDS B60
In High mode it took 28 sheets of paper, In primary 23 in Low mode 13
Then I took a 1W Luxeon generic light 25 sheets of paper
Then an Inova X1: 20 sheets of paper
Then I took a MiniMag and to my desbelief it took 28 sheets of paper to black it out, of course not even closed the E2E but as much as the HDS B60 in high mode. I put both lights together with the stack on top and the light penetration is almost the same.

So my first guess is that this tests light "penetration" and can be useful to measure what will happen in fog/rain conditions Leds are clearly inferior to incandescents in this area I need some fog or rain to see if the MiniMag can tie with the HDS B60.

I have more lights to test but I stopped when I found this since I was in shock.

Luigi

Just curious, how do the "hot spots" and reach(throw) of each light compare? Was the minimag focused to its tightest spot?

Yes, it is a mostly valid comparison test. You have created the "luigi index". While it does not measure any absolute units, it is a relative comparison of your lights using your paper.

It does not necessarily tell you much, because a very narrow beam will penetrate more sheets than a very wide beam of the same absolute output.

I am not sure if we will see sheets per lumen numbers in widespread use anytime soon.

Flash has a good point. Still it might be considered a valid test of throw.
Hrmmm, gotta think about this a bit.

flashfan said:

Just curious, how do the "hot spots" and reach(throw) of each light compare? Was the minimag focused to its tightest spot?

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Yes the Minimag was focused to the tightest spot. All the lights started with new batteries as well.

The variance in transmission properties could be accounted for by preferential absorption or reflection of certain wavelengths by the paper (i.e. the spectral absorption properties), combined with the spectral emission profiles of particular flashlights.

In other words, if the paper absorbs radiation within a certain wavelength range especially well, and a flashlight emits much of its radiation within that particular range, the Luigi Index may differ significantly from another flashlight that emits radiation across a different range of wavelengths, even if the measured lumen output is similar.

Here is a graph depicting the reflectance of cellulose (100% cotton bond paper), as a function of wavelength:



(Reference for the graph depicted above, USGS Spectroscopy Lab)

So a flashlight beam with a spectral profile with a bias towards that 2.104 micrometer wavelength will be absorbed by cellulose more than one with a spectral profile with a bias towards wavelengths on either side of that dip.

And here are some mind-numbingly boring papers containing absorption/reflectivity graphs of various types of paper:

The Darkening and Bleaching of Paper by Various Wavelengths in the Visible and Ultraviolet

Comments on the Measurement of "Yellowness" in Pulp and Paper

Google is a very dangerous thing...

Hmmm... what does this imply about the validity of all those white-wall beamshots that are posted on CPF? :naughty:

I believe Hookd is correct. Compare LEDs only, and just incans in a separate test to see if there is a closer correlation between the brighter lights and number of sheets required.

Unique idea, though!