On the lens protection film

Hello *@*,

recently I saw a bunch of posts dealing with the matter whether or not to leave the thin plastic lens protection film on the ARC LS optics.

If you want your ARC LS to be as /ubbthreads/images/graemlins/cool.gif bright /ubbthreads/images/graemlins/cool.gif as possible my advice is: *DO* take it off. The reasons for this are simple physics:

When light (or for that matter any electromagnetic radiation) is incident upon the boundary between two media, some of the energy is reflected and some undergoes refraction and is transmitted. There are several physical laws that govern the direction, amplitude, and phase of the reflected electromagnetic energy, but if one of the media is air, which has an index of refraction close to 1, then at normal incidence (the light propagates perpendicular to the surface of the glass) the reflectance for each surface is given by:

R = [(n-1)/(n+1)]2

where n is the index of refraction of the glass.

For glass with an index of refraction of 1.5 and negligible absorption, approximately 92% of the light will be transmitted though the glass and approximately 8% will be reflected (4% from each glass/air surface).

In multi-element systems, losing 4% of the incident energy at each surface can result in a significant overall loss of energy. For example, the total loss for ten common glass optics (n = 1.5) is over 60%. Optics with higher indices of refraction will suffer even larger reflection losses. Losses are also greater at higher angles of incidence. To prevent reflection losses, anti-reflection coatings that significantly reduce the fraction of incident energy reflected from each surface must be applied to each surface.

I don't know the exact index of refraction of the plastic film on the ARC LS lens but I suspect it to be even higher than that of glass, so the loss of light will probably be >8%. The ARC LS is already losing a significant amount of light energy in the optics mounted on the Luxeon Star, so away with the evil lens film I say. /ubbthreads/images/graemlins/twak.gif

-Connor /ubbthreads/images/graemlins/wink2.gif

I took mine off, but only becuz it had some lint and dust under it.

I would like to find some palm pc protective film to put back on it, and my GPS screen.

How easily is the Arc lens scratched? Can keys and such, in my pocket scratch it?

My LS is an older one and didn't come with this protector. I am particular about scratches on lenses and clear faceplates, so immediately after buying my LS, I made one for it. I cut a round protector, using a dime for the template, out of the clear plastic sheeting used by some people to cover table cloths and furniture. I used the thinnest gauge they had. I compared the light output visually with and without and I couldn't see a difference, so I cleaned the collimator and plastic with alcohol, dried it and static cling keeps it on.
Later, Arc started using them and I guess most people take theirs off. Peter said you can leave it on. I hope testing with and without the protector will be part of the big LS Output test he is having done.
Connor, thanks for the scientific explanation. I agree that it must reduce the output. It certainly isn't increasing it. It must be a small amount because I couldn't see a significant reduction.

I've also used this plastic over cell phone screens, GPS screen, Maglight lens, etc. If it gets scratched, I pull it off and replace it. This plastic is pretty scratch resistant, though.

My first use of this stuff was on my Palm Pilot in 1997. I figured the screen would get all scratched up by the stylus without something over it. So I put a piece of this plastic over it and it worked great. It didn't affect operation at all, and my Palm Pilot is still like new. Oh, how I wish I had marketed the idea, because about a year or two later, Write Right came out. /ubbthreads/images/graemlins/frown.gif

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jtice said:
I would like to find some palm pc protective film to put back on it, and my GPS screen.

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I saw an LCD maintenace kit at Best Buy that included some cleaning wipes and the LCD protective film.

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gyverpete said:
Connor, thanks for the scientific explanation. I agree that it must reduce the output. It certainly isn't increasing it. It must be a small amount because I couldn't see a significant reduction.

I've also used this plastic over cell phone screens, GPS screen, Maglight lens, etc. If it gets scratched, I pull it off and replace it. This plastic is pretty scratch resistant, though.


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Hi gyverpete,

I agree that it makes perfect sense to use some protection films on PDAs, GPS, cell phone screens etc. because these thingies tend to scratch up rather quickly.

But for normal use on an ARC LS? I mean, we're all here because we want the brightest, meanest, smallest flashlights on this planet .. so it seems rather weird to me to lessen the output of it (even if it's only ~8%) willingly. /ubbthreads/images/graemlins/thinking.gif

The Lexan lens of the ARC LS is quite small in diameter and also recessed and thus hard to reach or to be scratched. With some minor attention paid on where you put the light I think it will be free of scratches for a long time.

Freedom for all photons - outlaw ARC LS lens protection films! /ubbthreads/images/graemlins/yellowlaugh.gif

-Connor /ubbthreads/images/graemlins/wink2.gif

I know this must be something asked before but why doesn`t arc put a glass lens instead of the lexan? SF does it on their led flashlights. Why don`t they too?

Just wondering, since I haven`t had time to search for it, a short answer would be ok.

Thnx!
Alex

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AlexGT said:
.. a short answer would be ok.


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$

Money? Hardly... the reason the LS does not have a glass lens but a (coated) Lexan lens is fragility. /ubbthreads/images/graemlins/wink.gif

It has everything to do with being as "bulletproof" as possible. /ubbthreads/images/graemlins/thumbsup.gif

btw, Even on the older models without protection and/or extra film the scratching hardly is a problem. /ubbthreads/images/graemlins/grin.gif The lens is recessed, so somewhat protected already, and if anything should happen a plastic polish will take care of most of the (mostly just optical) problems... /ubbthreads/images/graemlins/rolleyes.gif

Is the lens replacable by mere mortals? I see the PCB is held in by a ring, if you take it out can you replace the lens? I'm sure someone (flashlightlens.com) could make one available is this were the case.

bj

(I just got my LSH on the independence sale. Oh My God. It's really nice)

Let us say "it has been done..." /ubbthreads/images/graemlins/wink.gif

The threads are locked with Locktite, so perseverance would be needed. /ubbthreads/images/graemlins/rolleyes.gif
I am not sure, but maybe in the future the lens will be easily user-replacable.

I took the plastic lens protector off as soon as I read about it in the instructions. I didn't know then that you could also leave it on. So my LSH-P has no more film on the lens. I don't know where the little plastic disc is anymore, but I guess I don't need it anymore. /ubbthreads/images/graemlins/tongue.gif

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AlexGT said:
... SF does it on their led flashlights. Why don`t they too?


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B@rt said:
Money? Hardly... the reason the LS does not have a glass lens but a (coated) Lexan lens is fragility. /ubbthreads/images/graemlins/wink.gif

It has everything to do with being as "bulletproof" as possible. /ubbthreads/images/graemlins/thumbsup.gif


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I thought Pyrex ("glass") is more expensive and "bulletproof" than Lexan /ubbthreads/images/graemlins/rant.gif

Pyrex is heat resistant. Probably more expensive since more breakage can occur in manufacturing.

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RY said:
I thought Pyrex ("glass") is more expensive and "bulletproof" than Lexan /ubbthreads/images/graemlins/rant.gif

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Pyrex is more heat resistant than Lexan and possibly more scratch resistant.

Lexan on the other hand is much more shatter resistant, less breakable, thus more 'bulletproof'.

On a side note, layers of Lexan are laminated between layers of glass to make glass bullet resistant.
Of course, bullet resistant glass is usually refered to as 'bulletproof'.

Pat

Somewhere around here is a long piece I wrote on why we use Lexan...

Basically, we believe it is some of the best material around. The most important quality (beside transparency) is its ability to withstand shock.

Remember, the two military guys that visited a couple of weeks ago? One of the odd things they told me was they have broken several SF Pyrex lenses in training. Seems they chip, crack and plain shatter when the light gets used hard.

Lexan can absorb more shock. They don't make bullet resistant "glass" out of Pyrex, they make it out of Lexan.

Believe me, cost is the not issue.

Sure, you can scratch the lens. But it is also easy to polish. This combination of shock resistance and easy service make for a long-lasting light.

Why do some manufacturers use Pyrex? Maybe because they buy a bunch of them for their incandescent lines. The old incandescents need them because they produce so much heat.

Peter

The traditional complaint about Lexan and other polycarbonates is that they scratch easily (which also means the scratches can be polished out easily). Lexan is just about unbreakable. If you hit it really hard, it tends to deform rather then break, and then pop out of what ever is holding it in place. It makes a great replacement for windows if you don't care about the scratches. People can throw rocks at Lexan all day and all they will do is scratch the surface.

In another forum here I told the story about the fire department attacking the lexan panel of a door with fire axes. The panels never did break, but the panel did pop out of the door, in one piece. (While the security guard was watching the fire department go to work,hold the door key in his hand...)

We could have put the panel back in the door, but it was sufficiently beat up from the multiple encounters with the fire axes that we figured we'd just replace it.

Another thing: If the pyrex lens cracks even a tiny bit, you may loose your waterproofness. Dropping the light transfers shockwaves through the housing and into the edges of the lens.

That same amount of force will cause the Lexan to just flex and return to normal without exposing the internals to the elements.

Peter

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gyverpete said:
It must be a small amount because I couldn't see a significant reduction.

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I wonder. I took a walk last night with the new LS without the protector and it seemed to be noticeably brighter at longer distances. (Not WAY brighter, but enough that I think I noticed things across a 3-lane highway that I hadn't seen before.)

Not sure if it has to do with the number of bubbles under the cover (mine had many) or if it's just my imagination. I don't think it's my imagination, though, because I'd taken off the cover after a discussion and forgot I'd done so. On the walk, I kept thinking, "Hmm... looks brighter. Maybe there's a break-in period on the regulator or something." So I wasn't looking for the cover to be the answer and finding what I wanted.

As I await delivery of mine from Vicomtel I'm thinking I'm going to be taking the cover off. I don't see any horror stories from owners of horribly scratched lenses. Given the EDC carry nature of the Arc and the fact that it therefore has been in near countless pockets with God knows how many sharp keys, I find this abscence encouraging.

Has anyone had any real problems with scratches?

So, Lexan it is. BTW what is the best polish for lexan? something easy to find in a local store. Trying to remember that someone posted a carwax or gunk of somesort that does it, can`t remember the name. what was it?

Alex