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Lighting: Fiber Optics

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  • Member since
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  • From: Huron, SD
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Lighting: Fiber Optics
Posted by Bayfield Transfer Railway on Sunday, July 5, 2020 9:43 PM

When you cut a length of fiber optic, say to attach to an LED for a headlight, is it necessary to polish the strand as in a communications fiber?  How do you polish it if necessary?  Or just cut it clean and don't worry?

Disclaimer:  This post may contain humor, sarcasm, and/or flatulence.

Michael Mornard

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Posted by RR_Mel on Sunday, July 5, 2020 10:24 PM

I have used a lot of fiber optics and having worked with fiber optic communications I did go all out polishing the fiber but over the years of using it for lighting on my layout polishing doesn’t help.  For the last couple of years I just cut it with flush cut wire cutters and I can’t tell any difference in my lighting.

Lately I have switched from regular 3mm LEDs to SMD 1206 micro LEDs with just a drop of CA/Super Glue on the LED and attach the fiber.  The SMD chip LEDs work better than the larger 3mm and 5mm LEDs.



Mel



 
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Posted by Bayfield Transfer Railway on Sunday, July 5, 2020 10:35 PM

Thanks for sharing.

Disclaimer:  This post may contain humor, sarcasm, and/or flatulence.

Michael Mornard

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Posted by RR_Mel on Sunday, July 5, 2020 11:31 PM

I stock from very small fiber to 3mm and just cut it with either wire cutters or a #11 blade.  I tried some 3mm Side Glow Fiber for passenger car lighting and while it worked wide angle 3mm LEDs work better.

I switched over to LED lighting for my HO vehicles but prefer incandescent lighting.  The 1mm incandescent micro bulbs are no longer available.  For 18 wheel tractor marker lights I bundle five .05mm fibers to a single amber 1206 LED using a short piece ⅛” D Styrene tubing.




Mel


 
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I'm beginning to realize that aging is not for wimps.
 

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Posted by Overmod on Monday, July 6, 2020 12:13 AM

The cement used to join the fiber end to the LED will couple the fiber optically without need for a formed lens, and this is likely true whether the fiber is glass or plastic core.

You're not concerned with many of the issues with high-speed polyspectral laser effects in the fiber, so precise termination and lensing are minor issues (by comparison with communications good practice)

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Posted by hon30critter on Monday, July 6, 2020 12:41 AM

Overmod
The cement used to join the fiber end to the LED will couple the fiber optically without need for a formed lens, and this is likely true whether the fiber is glass or plastic core.

Hi Overmod,

Are you referring to a specific cement for fiberoptics or cements in general like epoxy?

Thanks,

Dave

I'm just a dude with a bad back having a lot of fun with model trains, and finally building a layout!

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Posted by Overmod on Monday, July 6, 2020 4:57 AM

hon30critter
Are you referring to a specific cement for fiberoptics or cements in general like epoxy?

Probably anything that bonds to both the core end and the emitting face of the LED and dries reasonably clear.  I'm not certain as to the effect of 'matching' the refractive index of fiber core and cured adhesive (e.g. using one of the 'glass glue' products.

Epoxy in general requires a certain amount between the mating faces to form the strongest join, whereas something like cyanoacrylate not provided with filler benefits from very thin gap.  In both cases though the adhesion to the cut end should eliminate significant tendency for light to scatter or reflect from the cleaved end of the fiber.     

 

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Posted by SeeYou190 on Monday, July 6, 2020 8:35 AM

Overmod
Probably anything that bonds to both the core end and the emitting face of the LED and dries reasonably clear.

What brand of cement have you used that gives good results?

I have never attached fiber optic strands to the light source.

-Kevin

Wink Happily modeling my STRATTON & GILLETTE RAILROAD. A Class A line located in a personal fantasy world of semi-plausible nonsense on Tuesday, August 3rd, 1954.

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Posted by hon30critter on Tuesday, July 7, 2020 12:13 AM

SeeYou190
What brand of cement have you used that gives good results?

Hi Kevin,

If I can share my experience, I have used 90 minute epoxy with what I think are good results. I haven't tried CA because I was worried about it fracturing the fibres.

The challenge with epoxy is that it has to be held in place until it is completely hardened. If you let go of the fibre optic strand too soon, even when the epoxy seems to be stiff, the strand may still wander away from the focal point of the LED or lens. In my experience, the fibre optic strand has to be exactly centered on the lens or the LED or the amount of light transmitted will decrease significantly.

One trick to using fibre optic cables is to flare the end of the cable using a hot soldering iron or an open flame. This is particularly effective when forming headlight or tail light lenses. Here are a couple of older examples:

Dave

I'm just a dude with a bad back having a lot of fun with model trains, and finally building a layout!

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Posted by rrinker on Tuesday, July 7, 2020 7:42 AM

If you are using a regular 5mm LED< you can drill into the LED case slightly to inset the fiber. Then the only glue is on the outside, not between the end of the fiber and the light source. If you hold an LED up to the light, you should be able to see the little whisker wire into the top of the die inside - just don't drill down that far! The LED case is epoxy, so go slow.

                                 --Randy


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Posted by RR_Mel on Tuesday, July 7, 2020 7:57 AM

 

Dave

I’ve always used Super Glue/CA for attaching fiber to LEDs and never had a single problem.  When I bundle several fibers to a single LED I use a short (3/16”) piece of Evergreen Styrene Tubing as a holder.  I insert the ends into the tubing with a little over flow then apply the CA to the long side of the fibers and let the CA flow down inside the tube.

When it is fully anchored I use a #11 blade to trim the LED side of the fiber/tube flat then a drop of CA on the finished end and stick it to the LED.

If the bundle is large (5 or so) I power up the LED and tweak the fiber against the LED as the CA hardens to get max and even light out of the fiber ends.  Hold it for about a minute and your done.

Early on I used to heat the ends of the fiber for size and while that worked I have found using the correct size fiber cut clean looks better.

I use 2mm fiber for HO headlights (7”) .08mm for taillights (4”) and .05mm for marker lights.

Clean fiber cuts make for more realistic usable light from the fibers with less input.

 EDIT:

The SMD 1206 LEDs work much better then regular LEDs and their flat surface makes it easier too.


Mel


 
My Model Railroad   
http://melvineperry.blogspot.com/
 
Bakersfield, California
 
I'm beginning to realize that aging is not for wimps.
 

 

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Posted by woodone on Tuesday, July 7, 2020 8:43 AM

I have been using Bondic light activated glue. Then cover with heat shrink. The Bondic is clear so polishing the cable is not necessary.

The shrink reinforces the LED to the cable, and reduces light bleed.

 

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