Model Railroading > Light ‘Em Up! (Part 2) - Bending Light

I’ve always been fascinated with fiber optics.  The ability to transmit light through a “pipe”, has countless applications.  For the purposes of this project, its ability to create a pinpoint of light (remote from the light source) will be leveraged.  Because the Light Details have relatively low light intensity (vs. a ditch light), the high intensity of direct illumination from a LED is not required.
 
In Hot Water
The larger the diameter of a fiber, the more light it can transmit.  However, it becomes less flexible as the diameter increases.  When trying to navigate the fiber within the innards of a Tunnel Motor, trying to keep it out of sight, flexibility is a valuable asset.  If fiber needs to be used in tight spaces, a Pro Tip is to use hot water to bend it as shown in this Darwin video:
     youtube.com/watch?v=M5R1PqsjW58&t=7s
         (Cut-n-paste that into our browser.)
 
After removing it from the hot water, the fiber will cool, and the bend is permanent.
 
There are other heat sources that can be used to create the bend, but there is a narrow range of temperature where the fiber becomes flexible.  After that, it will melt and collapse.  Hot water provides not only a constant temperature, but heats all sides evenly, vs. just heating the side facing the heat source.
 
Gone Fishing
Though fishing line looks similar to fiber optics, it isn’t the same stuff.  It can transmit some light, but if paint is applied to the outside, light transmission diminishes significantly.  I’m all for saving a few bucks, but for 30’ @ $7, I played it safe and went with what will give me the greatest chance of long-term success. 
    https:/dwarvin.com/collections/ho-scale
I ordered the 4 smallest diameters.  The 1.5mm was too large for this project, but I may find a use for it on a future project.  The 1mm was a possibility, but probably more than necessary.  The 0.75mm was more flexible and could transmit a reasonable amount of light.  The 0.5mm was super flexible, and would be the easiest to hide.
 
Who's Your Buddy?
The 0.25mm is the fiber size supplied with the Step Lights from NixTrainz (the Decoder Buddy creator):
     https://nicknixtrainz.com/product-category/locolights/
The Step/Ground Light housings are 3D printed in clear resin.  There is a (3D printed) hole in the center of the fixture, thru which the fiber optic is threaded.  (This is a testament to the level of accuracy possible with 3D printed parts!)  I had to ream the hole with a drill bit to get the minuscule 0.25mm fiber to fit. The fact that there was already a pilot hole made this possible.  Without the 3D printed hole, it would be a struggle to drill a hole along the centerline of such a small part.

The outside of the fixture needs to be painted to prevent light bleed.  After experimenting with these, I will 3D print my own in black resin, to save a step (as well as eliminate the risk the paint will flake-off and create light bleed issues). 
 
Bulbs
If the end of the fiber is heated, it will ball-up.  This creates a very good representation of an incandescent bulb.  Provide light at the other end of the fiber, and the bulb will glow, projecting a prototypical amount of light.  (After heating the end, if the ball is too big or lop-sided, snip it off and try again.)  Let it cool.  Thread the other end thru the bottom of the Step Light fixture, and out the top.  Apply a bit of glue to the neck of the bulb.  Pull the fiber until it contacts the inside of the Step Light fixture.  Let the glue set.
 
The shape of the end of the fiber affects the pattern of light it projects.  If the end of the fiber is sheared-off clean, with a pair of sharp scissors, then it throws a sharp wedge of light.  If the end is melted into a bulb, then the light is spread-out in a wider and softer pattern.  This softer pattern looked the most realistic.  It casts light similar to a flood light (vs. a spot light).
 
Bendy-Straws
As an experiment, 3 strands of fiber (0.5mm fiber, 0.75mm, and 1mm diameter), were cut and bent to approximately 90-degrees. 
 
All used the same LED as the light source.  All were the same length, so the light had to travel the same distance.  The amount of light that was transmitted was reduced as the diameter became smaller.  However, the differences in light output were not as large as I anticipated.  I was pleasantly surprised to find that even the dinky 0.05mm fiber, with a tight bend, still transmitted a reasonable amount of light.  It is of particular interest because the 0.05mm would be the easiest to flex and hide in the shell. 
 
The 0.25mm fiber was compared with the 0.5mm fiber.  The 0.25mm fared reasonably well when kept straight.  However, with a sharp 90-degree bend, the light transmission suffered.  (A more gentle bend would help.)  There was enough light to be able to see it, but not enough intensity to illuminate the area. Possibly a candidate for a Step Light, but not a Ground Light. 
 
Darwin does not offer 0.25mm fiber.  I did find one site that offered it at 75 cents a foot, which was a bit steep.  Though I certainly don’t need 100 meters of it, Amazon had a deal on 0.25mm fiber I couldn’t refuse:
https://www.amazon.com/dp/B07Y1NMX4H?smid=A3L06Z631RS16Y&ref_=chk_typ_imgToDp&th=1

I knew fiber optic could transmit light, but was not sure if the smaller diameter fiber would perform well.  I had not used 0.25mm fiber before, and was encouraged by this round of tests.  

Dave
 



Edited 8 time(s). Last edit at 02/26/25 09:01 by tmotor.

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Thanks, this is a steps above what I have done with FO.
One use was to add clearaance and running lights to a bus and some trucks on our club layout.
The other is to use for a  short light tube to a headlight, I bore out the body light hole to 1/16" (0.0625") which works well with a 1 mm FO line or 3/64" for 1.5mm line.  (See pix)
For my locomotive ground lights I just place (with Goo) a pre-wired 402 LED behind the steps and run it through 82k resistance.  This makes it all but invisible under most "day" lighting conditons but quite pleasant to see at "dusk" or night.
I have had poor luck making the "bulb" end, but find that the end created with a sprue cutter makes a pretty good light, with a drop of clear canopy cement on the end to make it a rounded surface.



Edited 1 time(s). Last edit at 02/26/25 11:53 by railstiesballast.

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Greetings railstiesballast!

> Thanks, this is a steps above what I have done
> with FO.
> One use was to add clearaance and running lights
> to a bus and some trucks on our club layout.
> The other is to use for a  short light tube to a
> headlight, I bore out the body light hole to 1/16"
> (0.0625") which works well with a 1 mm FO line or
> 3/64" for 1.5mm line.  (See pix)
Perfect application for fiber optics!

> For my locomotive ground lights I just place (with
> Goo) a pre-wired 402 LED behind the steps and run
> it through 82k resistance. 
NICE!
Very clean install.
Everything is in-line, and compact.

> This makes it all but
> invisible under most "day" lighting conditons but
> quite pleasant to see at "dusk" or night.
EXCELLENT!
Just something subtle.  :-)
That is what I'm shooting for as well.

> I have had poor luck making the "bulb" end, but
> find that the end created with a sprue cutter
> makes a pretty good light, with a drop of clear
> canopy cement on the end to make it a rounded
> surface.
I will give that a try.  Sounds like I would have a higher success rate, especially with the dinky stuff.

Thank you for posting the images and sharing your expert advice.  :-D
Take care and God bless!
Dave

How much light comes through the side of the fiber optic, rather than the end?  I'm wondering if it would be suitable for making lighted switchstands in HO, using a short length of fiber lit by an LED below track level under the switchstand.

Pennsy3750:
I hink it would be too flimsy for even a short switch stand. If you want a fine scale switch stand that is lighted, use a piece of stainless steel micro tubing and place two pieces of coated magnet wire inside to light your lamp.The stainless steel tibing is solderable and comes in very small diameters right down to hyperdermic needles (too small for our needs.) But don't solder the tubing with the magnet wiring in it.

Victor Baird

Posted from Android



Edited 1 time(s). Last edit at 02/28/25 11:17 by wabash2800.

Greetings pennsy3750!

> How much light comes through the side of the fiber
> optic, rather than the end? 
Not a lot comes out the sides.  A coat of paint will take care of it.

> I'm wondering if it
> would be suitable for making lighted switchstands
> in HO, using a short length of fiber lit by an LED
> below track level under the switchstand.
That would be a GREAT application for fiber optics!
The fiber could be inserted just at the base of the shaft, and light the goes up the shaft to the marker lights on top.  That way if the stand is to operate, it is free to rotate.

Take care and God bless!
Dave
 

tmotor Wrote:
-------------------------------------------------------
> The fiber could be inserted just at the base of
> the shaft, and light the goes up the shaft to the
> marker lights on top

That's what I had in mind.  Assuming I find a marker light casting to sit on top of the shaft, would enough light shine through the side of the fiber?  It doesn't have to be super bright; just enough to tell its lit in a darkened room.

Sorry, I thought you meant to just mount the switch lamp on top of the strand of fiber optic. Dave,
would that be rigid enough? You could thread the fiber optic strand up through the micro tubing.

Victor Baird

Posted from Android



Edited 2 time(s). Last edit at 02/28/25 17:42 by wabash2800.

pennsy3750 Wrote:
-------------------------------------------------------
> How much light comes through the side of the fiber
> optic, rather than the end?  I'm wondering if it
> would be suitable for making lighted switchstands
> in HO, using a short length of fiber lit by an LED
> below track level under the switchstand.

Very little, unless you crack the outside.  I did that on my layout in college to try and create a sparkle effect in my waterfall.  It was a fun little experiment.  I also used fiber optics to light my deck mounted ditch lights for my GP60M that I kitbashed in college, that turned out pretty well.  Have it buried in a box somewhere, eventually it will get a DCC decoder and LEDs.

Nathan

Greetings pennsy3750!

> > The fiber could be inserted just at the base of
> > the shaft, and light the goes up the shaft to the
> > marker lights on top
> That's what I had in mind.  Assuming I find a
> marker light casting to sit on top of the shaft,
> would enough light shine through the side of the
> fiber?  It doesn't have to be super bright; just
> enough to tell its lit in a darkened room.
If the part is 3D printed in clear resin, then chances are very good.  The housing would be painted black, and the lenses would be Red and Green.
If the part is cast plastic or metal, then it would need to be hollow with Red and Green lenses.  That should work.
The best thing to do is buy one and try it.

Take care and God bless!
Dave



Edited 1 time(s). Last edit at 03/01/25 00:36 by tmotor.

Greetings Victor!

> Sorry, I thought you meant to just mount the
> switch lamp on top of the strand of fiber optic.
In that scenario, you are correct.

> Dave,
> would that be rigid enough?
Just about all fiber optics come in a roll.  This puts a natural curve in the material.  The larger diameter fiber (such as 0.75mm) could support an enclosure, but it would take some skill to remove the slight bend.

> You could thread the
> fiber optic strand up through the micro tubing.
Agreed.
The tubing is a great idea!  It is generally in straight sections.  The tubing you mentioned is available in ridiculously small tubing, like hypodermic needle sizes.  If the end of the fiber is at the base, the hollow center allows light to pass thru.  If too much light is lost, then the fiber can be shoved thru the tube until it reaches the enclosure with the lenses.

Take care and God bless!
Dave

Greetings Nathan!

> Very little, unless you crack the outside.  I did
> that on my layout in college to try and create a
> sparkle effect in my waterfall.  It was a fun
> little experiment.  
That is a VERY cool idea!  Having multiple fibers of various lengths, glued as the water fall.  the other end of the fibers point at a rotating disk.  On the other side of the disk is the light source.  The disk has perforations.  As the disk rotates, the light comes thru the penetrations, illuminating the fiber in the waterfall.  NICE!!  :-D

> I also used fiber optics to
> light my deck mounted ditch lights for my GP60M
> that I kitbashed in college, that turned out
> pretty well.  Have it buried in a box somewhere,
> eventually it will get a DCC decoder and LEDs.
Before the advent of the dinky SMD LEDs, that was the only option.  

Take care and God bless!
Dave

Dave:

Any idea what the smallest diameter of fibre optic strand available? Without looking too hard, I'm finding .030 (thirty thousands) which would be too thick for an HO stand, IMO. If nothing can be found smaller than that, I still advocate using very fine micro-tubing and running two coated magnet wires to a surface mounted LED inside a swath lamp casting (with colored lenses). If I were going to that much trouble for a scale size switch stand, I'd make it pivot from side to side when the swath is thrown. Bill Daraby wrote an article on how he did that some years ago in Model Railroader?

Victor Baird

Greetings Victor!

> Any idea what the smallest diameter of fibre optic
> strand available? Without looking too hard, I'm
> finding .030 (thirty thousands) which would be too
> thick for an HO stand,
The smallest I've found is 0.25mm, which is 0.00984252"
It is like a human hair!  :-O

> IMO. If nothing can be
> found smaller than that, I still advocate using
> very fine micro-tubing and running two coated
> magnet wires to a surface mounted LED inside a
> swath lamp casting (with colored lenses).
That could work.
The LED could also be at the base, and use the interior of the tube as a light pipe to illuminate the marker lights.

> If I
> were going to that much trouble for a scale size
> switch stand, I'd make it pivot from side to side
> when the swath is thrown.
Having it actually operate would be SWEET!  :-D

> Bill Daraby wrote an
> article on how he did that some years ago in Model
> Railroader?
I bet someone has written an article on this application.

Take care and God bless!
Dave