Light focusing tube

[Jan Panteltje]

On a sunny day (Tue, 13 Aug 2019 05:28:48 -0700 (PDT)) it happened
klaus.kragelund@gmail.com wrote in
<c842a656-a090-4cbd-80b0-89603d6d4631@googlegroups.com>:

On Tuesday, 13 August 2019 02:10:32 UTC+2, George Herold wrote:
On Monday, August 12, 2019 at 5:21:25 PM UTC-4, Klaus Kragelund wrote:
Hi

I need a light focusing tube, to turn a green led with viewing angle of
120 degrees down to a small spot

I was thinking about light reflective mylar, but am open to suggestions?


This is for test equipment, so anything goes =F0=9F=98=8A

Regards

Klaus

Huh, we use to electroplate copper onto SS cones... very long tapers,
a few degrees.. to focus FIR (say 10-100 um) onto a detector.
One grad student designed a parabolic reflector..
that did better. This is not for imaging, but just gathering as many
photons as possible.

What about a lens?

Lens could be an option, but has to be indifferent to the length from the object,
so it is robust against production changes

I did this once, optical fiber in hole drilled in normal LED:
http://panteltje.com/pub/optical_fiber_in_LED_IMG_0138.JPG
VERY small spot close to the end of the fibre.
Just one of those experiments, probably not of much use in this case.

 

[Martin Brown]

On 13/08/2019 13:32, klaus.kragelund@gmail.com wrote:

On Tuesday, 13 August 2019 10:43:37 UTC+2, Martin Brown wrote:
On 12/08/2019 22:21, Klaus Kragelund wrote:
Hi

I need a light focusing tube, to turn a green led with viewing angle of 120 degrees down to a small spot

Why not use an LED with a much narrower viewing angle?
15 degrees is relatively common eg

https://www.rapidonline.com/truopto-ospg5111a-vw-5mm-3-3v-green-led-high-brightness-15-55-1816

At that low beam divergence it might already be good enough on its own
or with a small lens in front.


Yes, could help to find an alternative LED with more focus from the get go

I have just seen that you are using a 5W unit. Some of them have clip on
kits to add a plastic parabolic collimator that might do what you want.

Generally the ones used in "please don't hit me lamps" on police cars etc.

https://uk.rs-online.com/web/p/products/6656735/?grossPrice=Y&cm_mmc=UK-PLA-DS3A-_-bing-_-PLA_UK_EN_Displays_And_Optoelectronics-_-Led_Lighting_System_Components%7CLed_Reflectors-_-PRODUCT+GROUP&matchtype=e&pla-4574655567267318&msclkid=1bc025289b3b137ab95b787a23b0b724&gclid=CPChlsf3_-MCFYMcGwodW1oDNA&gclsrc=ds

Sorry about the wacky long URL. Google clip on reflector LED.

--
Regards,
Martin Brown

 

[Rick C]

On Tuesday, August 13, 2019 at 8:29:53 AM UTC-4, klaus.k...@gmail.com wrote:

On Tuesday, 13 August 2019 02:31:50 UTC+2, Rick C wrote:
On Monday, August 12, 2019 at 6:15:09 PM UTC-4, klaus.k...@gmail.com wrote:
On Monday, 12 August 2019 23:48:51 UTC+2, pcdh...@gmail.com wrote:
How small a spot?


The emitting LED chip is 1mm2, the receiving LED has a housing of 1mm2, but a chip of about 0.1mm2. So I would be happy to have the spot of just less than 5mm2. I am ballparking here, I would like the spot to be bigger than the receiving LED, so that I can have production equipment that does not need to be top notch to "cover" the receiving LED in photons

Does this require nothing in between? Can you use a light pipe? They are common to illuminate front panels from LEDs on the board behind. If the path is straight the light pipe just becomes a plastic cylinder. They make them in many shapes and sizes with various attachments.

Light pipe is a good idea. Don't know how much light is lost in a pipe, found no numbers in the datasheets I looked into

They work with total internal reflection, so I think very little. Look at one in operation. You don't see much light lost extraneously. A light pipe does not act as a collimator. They essentially make the light appear as if it is coming from a closer point. But light at too wide an angle is outside the angle of total reflection so is not conveyed.

--

Rick C.

+ Get 1,000 miles of free Supercharging
+ Tesla referral code - https://ts.la/richard11209

 

[Rick C]

On Tuesday, August 13, 2019 at 8:28:52 AM UTC-4, klaus.k...@gmail.com wrote:

On Tuesday, 13 August 2019 02:10:32 UTC+2, George Herold wrote:
On Monday, August 12, 2019 at 5:21:25 PM UTC-4, Klaus Kragelund wrote:
Hi

I need a light focusing tube, to turn a green led with viewing angle of 120 degrees down to a small spot

I was thinking about light reflective mylar, but am open to suggestions?

This is for test equipment, so anything goes 😊

Regards

Klaus

Huh, we use to electroplate copper onto SS cones... very long tapers,
a few degrees.. to focus FIR (say 10-100 um) onto a detector.
One grad student designed a parabolic reflector..
that did better. This is not for imaging, but just gathering as many
photons as possible.

What about a lens?

Lens could be an option, but has to be indifferent to the length from the object, so it is robust against production changes

It is unclear what "object" is here. If the variable distance object is the receiver, you could use two lenses. The first focuses the light to a small diameter point and the second lens makes the light into a parallel beam from that point. Then the beam will have low divergence over a range of distance.

If the "object" is the light source and the lens is on the receiver, you are screwed I think. You can't use a lens.

--

Rick C.

-- Get 1,000 miles of free Supercharging
-- Tesla referral code - https://ts.la/richard11209

 

[Rick C]

On Tuesday, August 13, 2019 at 8:34:10 AM UTC-4, klaus.k...@gmail.com wrote:

On Tuesday, 13 August 2019 11:04:13 UTC+2, piglet wrote:
On 12/08/2019 10:21 pm, Klaus Kragelund wrote:
Hi

I need a light focusing tube, to turn a green led with viewing angle of 120 degrees down to a small spot

I was thinking about light reflective mylar, but am open to suggestions?

This is for test equipment, so anything goes 😊

Regards

Klaus


A long metal tube shiny on the inside?

piglet

Yes, that is what I was looking for when talking about the reflective mylar

Maybe a problem with the extreme angles (120 degrees), that just bounces back and forth between the inner sides of the tube, and when it escapes the end of the tube it still has 120 degrees?

Yes, exactly. A light pipe will be the same, but 120 degree light most likely won't be reflected to the destination end at all. lol

--

Rick C.

-+ Get 1,000 miles of free Supercharging
-+ Tesla referral code - https://ts.la/richard11209

 

[Martin Brown]

On 13/08/2019 01:10, George Herold wrote:

On Monday, August 12, 2019 at 5:21:25 PM UTC-4, Klaus Kragelund wrote:
Hi

I need a light focusing tube, to turn a green led with viewing angle of 120 degrees down to a small spot

I was thinking about light reflective mylar, but am open to suggestions?

This is for test equipment, so anything goes 😊

Regards

Klaus

Huh, we use to electroplate copper onto SS cones... very long tapers,
a few degrees.. to focus FIR (say 10-100 um) onto a detector.
One grad student designed a parabolic reflector..
that did better. This is not for imaging, but just gathering as many
photons as possible.

Its a classic approach when using photomultipliers in huge tanks of
liquid neutrino detectors to catch as many photons as possible with the
smallest number of tubes. Also for non-focussing solar concentrators.

The analytic solution for a device that causes every ray path that
enters the front aperture to hit the target (eventually) is a pair of
parabolas placed so that they each have their focus at the base of the
other.

https://www.sciencedirect.com/sdfe/pdf/download/eid/1-s2.0-0038092X77900615/first-page-pdf

Is a reasonable introduction.

--
Regards,
Martin Brown

 

[Jeff Liebermann]

On Mon, 12 Aug 2019 14:21:21 -0700 (PDT), Klaus Kragelund
<klauskvik@hotmail.com> wrote:

I need a light focusing tube, to turn a green led with viewing angle of 120 degrees down to a small spot
I was thinking about light reflective mylar, but am open to suggestions?
This is for test equipment, so anything goes ?

Fiberoptic light pipe:
<https://www.mouser.com/Optoelectronics/LED-Indication/LED-Light-Pipes/_/N-b1d20?P=1yzug3o>
The 60 degree entry angle worries me. I guess try it and see if the
pipe grabs all the light, or just get a wide diameter fat pipe. There
are adapaters to install a lens on the end.
<https://www.google.com/search?q=fiber+optic+light+pipes+led&tbm=isch>
Some interesting stuff:
<https://i-fiberoptics.com/engineering.php?summary=104&cat=light-pipe-kits>



--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

 

[Jon Elson]

On Mon, 12 Aug 2019 14:21:21 -0700, Klaus Kragelund wrote:

Hi

I need a light focusing tube, to turn a green led with viewing angle of
120 degrees down to a small spot

Many years ago, I wanted to build a laser photoplotter, for making PCB
artwork. After fooling around with LEDS and conical concentrator schemes
for a while, I got the first red lasers when they came onto the surplus
market (kind of dates the project). I used a 3 mm sphere lens almost
touching the front of the laser to collimated the laser as well as I
could. Then, I put a pinhole in front of the sphere lens, to get rid of
light off the edge. Then, I had a 13 mm F.L. microfiche objective lens
to focus onto the film. My rig actually has a double-meniscus lens in
the middle, to make the spot smaller. I'm not sure that is actually
needed, but it all works. It can produce a 670 nm red spot so much
smaller than the .001" stepover that I have to slightly defocus the thing
so the raster lines merge together.

Jon

 

[Mike Coon]

In article <53fc3aaa-937c-4995-a31c-f2a6a72e8673@googlegroups.com>,
gnuarm.deletethisbit@gmail.com says...

Light pipe is a good idea. Don't know how much light is lost in a
pipe, found no numbers in the datasheets I looked into

They work with total internal reflection, so I think very little.
Look at one in operation. You don't see much light lost extraneously.

But that is only one source of loss; there is also absorption. You won't
be able to see that. Presumably a pipe made for the purpose will be a
good quality optical material...

Mike.

 

[Jon Elson]

On Tue, 13 Aug 2019 05:29:49 -0700, klaus.kragelund wrote:

Light pipe is a good idea. Don't know how much light is lost in a pipe,
found no numbers in the datasheets I looked into

You could get some Lucite/Plexiglas rod, and heat the middle of it until
it softens, then pull the ends. This will neck down the middle. Then,
cut at the desired small-end diameter and polish. But, some physics
papers claim that you cannot concentrate light this way. I'm not
convinced.

Jon

 

[John Larkin]

On Tue, 13 Aug 2019 05:27:55 -0700 (PDT), klaus.kragelund@gmail.com
wrote:

On Tuesday, 13 August 2019 01:55:38 UTC+2, jla...@highlandtechnology.com wrote:
On Mon, 12 Aug 2019 14:21:21 -0700 (PDT), Klaus Kragelund
klauskvik@hotmail.com> wrote:

Hi

I need a light focusing tube, to turn a green led with viewing angle of 120 degrees down to a small spot

I was thinking about light reflective mylar, but am open to suggestions?

This is for test equipment, so anything goes ?

Regards

Klaus

Are you trying to change the way the LED looks, or are you trying to
project a spot onto some distant surface?


Project a spot

You probably need a flat-face LED and a lens. I don't think a tube
would work.

How about a laser? Pointer type red lasers are absurdly cheap.

 

[George Herold]

On Tuesday, August 13, 2019 at 2:46:49 PM UTC-4, Jon Elson wrote:

On Tue, 13 Aug 2019 05:29:49 -0700, klaus.kragelund wrote:


Light pipe is a good idea. Don't know how much light is lost in a pipe,
found no numbers in the datasheets I looked into
You could get some Lucite/Plexiglas rod, and heat the middle of it until
it softens, then pull the ends. This will neck down the middle. Then,
cut at the desired small-end diameter and polish. But, some physics
papers claim that you cannot concentrate light this way. I'm not
convinced.

If there is a tapper in the tube and it becomes a cone, then for
short wavelengths, (compared to the tube size) you can use
ray tracing, with angle of incidence = reflection, when you try
and focus this way you have to 'give up' some light.


(for a reflecting cone it's a battle between the angle,
number of reflections, and the loss per reflection..
Photons entering at large angles have to reflect too many

At some wavelength fiber/ glass may become 'better' than
a metal reflector.

Our tapered tubes where for collecting light from a source that
had already been collimated (sp) and sent through a FIR scanning
interferometer. With an extended source (LED into ~120 deg)*
collecting ~1/2 the photons is hard enough...
if you want to focus them you've got to give up more.

George H.
*Hey LED's are giving up 1/2 their photons to the back...
anyone putting a reflector in the back?
(might be a little cooler too?)

Jon

 

[Jan Panteltje]

On a sunny day (Tue, 13 Aug 2019 17:28:52 -0700 (PDT)) it happened George
Herold <gherold@teachspin.com> wrote in
<0a838f8f-356a-4ecf-b117-26449bc37c54@googlegroups.com>:

*Hey LED's are giving up 1/2 their photons to the back...
anyone putting a reflector in the back?
(might be a little cooler too?)

Open up a LED, some have a small hollow mirror like structure that the
emitting part is mounted on:

..)-----------
| __________

 

[George Herold]

On Tuesday, August 13, 2019 at 3:27:35 PM UTC-4, John Larkin wrote:

On Tue, 13 Aug 2019 05:27:55 -0700 (PDT), klaus.kragelund@gmail.com
wrote:

On Tuesday, 13 August 2019 01:55:38 UTC+2, jla...@highlandtechnology.com wrote:
On Mon, 12 Aug 2019 14:21:21 -0700 (PDT), Klaus Kragelund
klauskvik@hotmail.com> wrote:

Hi

I need a light focusing tube, to turn a green led with viewing angle of 120 degrees down to a small spot

I was thinking about light reflective mylar, but am open to suggestions?

This is for test equipment, so anything goes ?

Regards

Klaus

Are you trying to change the way the LED looks, or are you trying to
project a spot onto some distant surface?


Project a spot


You probably need a flat-face LED and a lens. I don't think a tube
would work.

How about a laser? Pointer type red lasers are absurdly cheap.

Lasers are way better than LED's as light sources.
Above threshold, except for losses at the end reflectors,
every extra electron turns into a photon...
hmm, I think that's right?

George H.

 

Jan Panteltje <pNaOnStPeAlMtje@yahoo.com> wrote in
news:qivo1q$lvc$1@dont-email.me:

On a sunny day (Tue, 13 Aug 2019 17:28:52 -0700 (PDT)) it happened
George Herold <gherold@teachspin.com> wrote in
0a838f8f-356a-4ecf-b117-26449bc37c54@googlegroups.com>:

*Hey LED's are giving up 1/2 their photons to the back...
anyone putting a reflector in the back?
(might be a little cooler too?)

Open up a LED, some have a small hollow mirror like structure that
the emitting part is mounted on:

.)-----------
| __________

Those are the lame low current traditional design jobs that have
been around for decades.

The high output high wattage jobs are not configured that way (no
tiny dish) and all their light is directed forward.

$1.82 each

<https://www.digikey.com/product-detail/en/cree-inc/XPEBRO-L1-0000-
00D01/XPEBRO-L1-0000-00D01CT-ND/5806148>

 

[whit3rd]

On Monday, August 12, 2019 at 3:15:09 PM UTC-7, klaus.k...@gmail.com wrote:

The emitting LED chip is 1mm2, the receiving LED has a housing of 1mm2, but a chip of about 0.1mm2. So I would be happy to have the spot of just less than 5mm2.

A nominal 120 degrees of spread includes most of the light, so a 5mm 'pencil' beam
would result from a lens greater-or-equal to 5mm diameter, at a distance of its focal
length (so the lens acts as a collimator). Minimum focal distance would be the
distance at which 120 degree spread from a point hits the 5mm diameter, about
(5mm * cot(120deg/2) )/2 =1.44 millimeters

That doesn't seem practical (it'll waste lots of light if you let it spread farther), but
it gives you a pencil beam for a long working distance. A light pipe will put the
5mm spot at end B after cementing the LED to end A, but light spreads at the
120 degrees starting at end B (so do you really want a light pipe butted against
the receiver?).

A laser with a telescope-like 'beam expander' can give collimated light, too, but
it's nice to have some diffusion (because the 'spot' might have more light/dark
modulation than you'd like, and only the small receiver area is sensed, not the average).

The best light concentration, alas, results from focusing NOT to a pencil beam, but
to an image of the emitting die (and that, too, doesn't usually look like a
uniform illuminated spot).

 

[nuny@bid.nes]

On Tuesday, August 13, 2019 at 5:28:52 AM UTC-7, klaus.k...@gmail.com wrote:

On Tuesday, 13 August 2019 02:10:32 UTC+2, George Herold wrote:
On Monday, August 12, 2019 at 5:21:25 PM UTC-4, Klaus Kragelund wrote:
Hi

I need a light focusing tube, to turn a green led with viewing angle
of 120 degrees down to a small spot

I was thinking about light reflective mylar, but am open to suggestions?

This is for test equipment, so anything goes 😊

Regards

Klaus

Huh, we use to electroplate copper onto SS cones... very long tapers,
a few degrees.. to focus FIR (say 10-100 um) onto a detector.
One grad student designed a parabolic reflector..
that did better. This is not for imaging, but just gathering as many
photons as possible.

What about a lens?

Lens could be an option, but has to be indifferent to the length from
the object, so it is robust against production changes

Sounds more and more like you need a cheap laser diode w/driver then, not an LED. Does the spot of light *have* to be green?


Mark L. Fergerson

 

[Jasen Betts]

On 2019-08-13, klaus.kragelund@gmail.com <klaus.kragelund@gmail.com> wrote:

On Tuesday, 13 August 2019 09:31:26 UTC+2, Jasen Betts wrote:
On 2019-08-12, Klaus Kragelund <klauskvik@hotmail.com> wrote:
Hi

I need a light focusing tube, to turn a green led with viewing angle of 120 degrees down to a small spot

Which LED, how small?

Can you use an SMD LED instead?

I cannot use a smaller LED. This one is a 5W++ one, so has a certain size

I guess you need some sort of lens then, but you cannot focus the spot any
smaller than the LED die because entropy.

--
When I tried casting out nines I made a hash of it.

 

[Carl]

On Tuesday, August 13, 2019 at 5:28:52 AM UTC-7, klaus.k...@gmail.com
wrote:
On Tuesday, 13 August 2019 02:10:32 UTC+2, George Herold wrote:
On Monday, August 12, 2019 at 5:21:25 PM UTC-4, Klaus Kragelund wrote:
Hi

I need a light focusing tube, to turn a green led with viewing angle
of 120 degrees down to a small spot

I was thinking about light reflective mylar, but am open to
suggestions?

This is for test equipment, so anything goes 😊

Regards

Klaus

Huh, we use to electroplate copper onto SS cones... very long tapers,
a few degrees.. to focus FIR (say 10-100 um) onto a detector.
One grad student designed a parabolic reflector..
that did better. This is not for imaging, but just gathering as many
photons as possible.

What about a lens?

Lens could be an option, but has to be indifferent to the length from
the object, so it is robust against production changes

Sounds to me like you are down to either an acrylic cylindrical light tube
in contact with led and detector and just take whatever spot you get on the
detector, or define what you mean by "indifferent to the length from the
object" to see if the depth of focus you can get from a collimation lens is
sufficient and accept that the spot will always be larger than your
detector.

--
Regards,
Carl Ijames

 

[Jan Panteltje]

I wrote

Open up a LED, some have a small hollow mirror like structure that the
emitting part is mounted on:

.)-----------
| __________

Like this:
http://panteltje.com/pub/white_LED_back_reflector_IXIMG_0143.JPG
and
http://panteltje.com/pub/white_LED_back_reflector_IXIMG_0144.JPG