DIY reflector paint

[Klaus Kragelund]

Hi

I have a prototype setup where I need to turn a 145 degree intensity field from a LED into a parallel field

There is no readily available lenses so I was thinking about 3D printing PLA to make a custom reflector

But then I need reflective paint. What can I use, a chrome paint or?

Cheers

Klaus

 

Klaus Kragelund <klauskvik@hotmail.com> wrote in
news:d0dfbdd7-6d0d-4a36-a526-05ca49283a1c@googlegroups.com:

Hi

I have a prototype setup where I need to turn a 145 degree
intensity field from a LED into a parallel field

There is no readily available lenses so I was thinking about 3D
printing PLA to make a custom reflector

But then I need reflective paint. What can I use, a chrome paint
or?

Cheers

Klaus

Nothing hand applied would be good.

Do a youtube search for aluminum sputtering or mirroring. Or Bismuth
or... other. But there are metallization videos out there I am
sure.

And model car makers used to chrome plastic trees full of 'parts'
for our models. So it can't be too hard to metallize it.
Electroplating follows the surface it is put on though so your 3D
printed part would have to have some good surfaces on it where you
want the mirroring to be or you would have to post process them
before you 'chrome' it.

 

[Phil Hobbs]

On 2020-02-07 13:01, Klaus Kragelund wrote:

Hi

I have a prototype setup where I need to turn a 145 degree intensity
field from a LED into a parallel field

There is no readily available lenses so I was thinking about 3D
printing PLA to make a custom reflector

But then I need reflective paint. What can I use, a chrome paint or?

Cheers

Klaus

A paraboloidal mirror is your friend. You can also get a LED reflector:

ASSY REFLECTOR LUMAWISE 10DEG 43MM SNAP 1-2154430-1 TE Conn $3

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

[Rick C]

On Friday, February 7, 2020 at 1:01:34 PM UTC-5, Klaus Kragelund wrote:

Hi

I have a prototype setup where I need to turn a 145 degree intensity field from a LED into a parallel field

There is no readily available lenses so I was thinking about 3D printing PLA to make a custom reflector

But then I need reflective paint. What can I use, a chrome paint or?

What about total internal reflection? Is that viable in this case? Can you get the geometry to work?

--

Rick C.

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

 

[Dave Platt]

In article <d0dfbdd7-6d0d-4a36-a526-05ca49283a1c@googlegroups.com>,
Klaus Kragelund <klauskvik@hotmail.com> wrote:

Hi

I have a prototype setup where I need to turn a 145 degree intensity field from a LED into a parallel field

There is no readily available lenses so I was thinking about 3D printing PLA to make a custom reflector

But then I need reflective paint. What can I use, a chrome paint or?

It sounds as if what you want to do, is something vaguely similar to
what Bausch & Lomb did with their "Nicholas" illuminator for their
stereo microscopes. If I recall correctly the B&L Nicholas
illuminator uses both lenses, and a reflective tube to collimate the
beam.

Any sort of paint I can think of, is going to turn your reflector
surface into a diffuser... the unevenness of the paint surface is
going to be quite a few wavelengths. You'll get a lot of light coming
off of it at angles which result in a "sort of parallel" field,
overall... that may or may not be adequate for your application. If
you just need effective illumination, maybe so... if you're expecting
sharp-edged shadows, probably not.

If you really do need a well-collimated beam, you're going to need
something approaching an optically-accurate reflective surface. To me
that suggests "smooth it carefully, buff on some graphite, and then
electroplate it". A commercial silver-plating company might be able
to deposit-and-polish.

I suspect that a lens-based approach is likely to be easier to get
working properly. Sure you can't find anything in Edmund's catalog
which could be pressed into service?

 

[Phil Hobbs]

On 2020-02-07 14:26, Dave Platt wrote:

In article <d0dfbdd7-6d0d-4a36-a526-05ca49283a1c@googlegroups.com>,
Klaus Kragelund <klauskvik@hotmail.com> wrote:
Hi

I have a prototype setup where I need to turn a 145 degree intensity field from a LED into a parallel field

There is no readily available lenses so I was thinking about 3D printing PLA to make a custom reflector

But then I need reflective paint. What can I use, a chrome paint or?

It sounds as if what you want to do, is something vaguely similar to
what Bausch & Lomb did with their "Nicholas" illuminator for their
stereo microscopes. If I recall correctly the B&L Nicholas
illuminator uses both lenses, and a reflective tube to collimate the
beam.

Any sort of paint I can think of, is going to turn your reflector
surface into a diffuser... the unevenness of the paint surface is
going to be quite a few wavelengths. You'll get a lot of light coming
off of it at angles which result in a "sort of parallel" field,
overall... that may or may not be adequate for your application. If
you just need effective illumination, maybe so... if you're expecting
sharp-edged shadows, probably not.

If you really do need a well-collimated beam, you're going to need
something approaching an optically-accurate reflective surface. To me
that suggests "smooth it carefully, buff on some graphite, and then
electroplate it". A commercial silver-plating company might be able
to deposit-and-polish.

I suspect that a lens-based approach is likely to be easier to get
working properly. Sure you can't find anything in Edmund's catalog
which could be pressed into service?

Lenses are heartbreakingly inefficient for this job, trust me. A
large-aperture paraboloid with the LED at the focus (pointing at the
mirror) is the ticket.

LEDs are spatially incoherent, and so radiate into a hemisphere (pi
steradians projected solid angle). The projected solid angle of a lens
with a given numerical aperture is pi*NA**2. (A hemisphere corresponds
to NA=1.) So the light collection efficiency of a lens is just NA**2.

A super-large aperture lens, such as 25 mm FL, 25 mm diameter, has an NA
of 0.5, meaning that it collects only a quarter of the light. It also
has horrible aberrations, so the collimated beam quality is poor. Most
lens-based condenser systems are much less efficient than that--a 100 mm
FL lens of 25 mm diameter collects only 1/64 of the light.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

[Klaus Kragelund]

On Friday, February 7, 2020 at 7:37:04 PM UTC+1, Phil Hobbs wrote:

On 2020-02-07 13:01, Klaus Kragelund wrote:
Hi

I have a prototype setup where I need to turn a 145 degree intensity
field from a LED into a parallel field

There is no readily available lenses so I was thinking about 3D
printing PLA to make a custom reflector

But then I need reflective paint. What can I use, a chrome paint or?

Cheers

Klaus


A paraboloidal mirror is your friend. You can also get a LED reflector:

ASSY REFLECTOR LUMAWISE 10DEG 43MM SNAP 1-2154430-1 TE Conn $3

The LED I am using is this one:

https://www.lumileds.com/uploads/265/DS68-pdf

I have tried parabolic reflector, but due to the construction of the PCB I could not position the LED in the focus point


Maybe I should redo the setup, since I think you are right, the off the shelf reflector is a lot easier

Cheers

Klaus

 

[John Larkin]

On Fri, 7 Feb 2020 10:01:25 -0800 (PST), Klaus Kragelund
<klauskvik@hotmail.com> wrote:

Hi

I have a prototype setup where I need to turn a 145 degree intensity field from a LED into a parallel field

There is no readily available lenses so I was thinking about 3D printing PLA to make a custom reflector

But then I need reflective paint. What can I use, a chrome paint or?

Cheers

Klaus

3D printing is slow and makes gritty surfaces.

Maybe press aluminum foil into a mold?

Vacuum forming can be cool. I wonder if you could vac form aluminized
plastic.

There's probably a suitable cheap reflector already available
somewhere. Maybe in a car tail-light or something.



--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

 

[Klaus Kragelund]

On Friday, February 7, 2020 at 8:39:16 PM UTC+1, Phil Hobbs wrote:

On 2020-02-07 14:26, Dave Platt wrote:
In article <d0dfbdd7-6d0d-4a36-a526-05ca49283a1c@googlegroups.com>,
Klaus Kragelund <klauskvik@hotmail.com> wrote:
Hi

I have a prototype setup where I need to turn a 145 degree intensity field from a LED into a parallel field

There is no readily available lenses so I was thinking about 3D printing PLA to make a custom reflector

But then I need reflective paint. What can I use, a chrome paint or?

It sounds as if what you want to do, is something vaguely similar to
what Bausch & Lomb did with their "Nicholas" illuminator for their
stereo microscopes. If I recall correctly the B&L Nicholas
illuminator uses both lenses, and a reflective tube to collimate the
beam.

Any sort of paint I can think of, is going to turn your reflector
surface into a diffuser... the unevenness of the paint surface is
going to be quite a few wavelengths. You'll get a lot of light coming
off of it at angles which result in a "sort of parallel" field,
overall... that may or may not be adequate for your application. If
you just need effective illumination, maybe so... if you're expecting
sharp-edged shadows, probably not.

If you really do need a well-collimated beam, you're going to need
something approaching an optically-accurate reflective surface. To me
that suggests "smooth it carefully, buff on some graphite, and then
electroplate it". A commercial silver-plating company might be able
to deposit-and-polish.

I suspect that a lens-based approach is likely to be easier to get
working properly. Sure you can't find anything in Edmund's catalog
which could be pressed into service?


Lenses are heartbreakingly inefficient for this job, trust me. A
large-aperture paraboloid with the LED at the focus (pointing at the
mirror) is the ticket.

LEDs are spatially incoherent, and so radiate into a hemisphere (pi
steradians projected solid angle). The projected solid angle of a lens
with a given numerical aperture is pi*NA**2. (A hemisphere corresponds
to NA=1.) So the light collection efficiency of a lens is just NA**2.

A super-large aperture lens, such as 25 mm FL, 25 mm diameter, has an NA
of 0.5, meaning that it collects only a quarter of the light. It also
has horrible aberrations, so the collimated beam quality is poor. Most
lens-based condenser systems are much less efficient than that--a 100 mm
FL lens of 25 mm diameter collects only 1/64 of the light.

We did try with a lense and a fiberoptic cable. The loss was horific. So like you say, I will need to try another solution and the reflector looks good

 

[John Larkin]

On Fri, 7 Feb 2020 14:39:04 -0500, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

On 2020-02-07 14:26, Dave Platt wrote:
In article <d0dfbdd7-6d0d-4a36-a526-05ca49283a1c@googlegroups.com>,
Klaus Kragelund <klauskvik@hotmail.com> wrote:
Hi

I have a prototype setup where I need to turn a 145 degree intensity field from a LED into a parallel field

There is no readily available lenses so I was thinking about 3D printing PLA to make a custom reflector

But then I need reflective paint. What can I use, a chrome paint or?

It sounds as if what you want to do, is something vaguely similar to
what Bausch & Lomb did with their "Nicholas" illuminator for their
stereo microscopes. If I recall correctly the B&L Nicholas
illuminator uses both lenses, and a reflective tube to collimate the
beam.

Any sort of paint I can think of, is going to turn your reflector
surface into a diffuser... the unevenness of the paint surface is
going to be quite a few wavelengths. You'll get a lot of light coming
off of it at angles which result in a "sort of parallel" field,
overall... that may or may not be adequate for your application. If
you just need effective illumination, maybe so... if you're expecting
sharp-edged shadows, probably not.

If you really do need a well-collimated beam, you're going to need
something approaching an optically-accurate reflective surface. To me
that suggests "smooth it carefully, buff on some graphite, and then
electroplate it". A commercial silver-plating company might be able
to deposit-and-polish.

I suspect that a lens-based approach is likely to be easier to get
working properly. Sure you can't find anything in Edmund's catalog
which could be pressed into service?


Lenses are heartbreakingly inefficient for this job, trust me. A
large-aperture paraboloid with the LED at the focus (pointing at the
mirror) is the ticket.

LEDs are spatially incoherent, and so radiate into a hemisphere (pi
steradians projected solid angle). The projected solid angle of a lens
with a given numerical aperture is pi*NA**2. (A hemisphere corresponds
to NA=1.) So the light collection efficiency of a lens is just NA**2.

A super-large aperture lens, such as 25 mm FL, 25 mm diameter, has an NA
of 0.5, meaning that it collects only a quarter of the light. It also
has horrible aberrations, so the collimated beam quality is poor. Most
lens-based condenser systems are much less efficient than that--a 100 mm
FL lens of 25 mm diameter collects only 1/64 of the light.

Cheers

Phil Hobbs

Might a Fresnel be better here?

--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

 

[Cursitor Doom]

On Fri, 7 Feb 2020 10:01:25 -0800 (PST), Klaus Kragelund
<klauskvik@hotmail.com> wrote:

Hi

I have a prototype setup where I need to turn a 145 degree intensity field from a LED into a parallel field

There is no readily available lenses so I was thinking about 3D printing PLA to make a custom reflector

But then I need reflective paint. What can I use, a chrome paint or?

That stuff is garbage. IME there's nothing better than carefully cut
and pasted strips of kitchen foil. Unless you want to splash out and
get the thing professionally silvered, of course.

 

[Jasen Betts]

On 2020-02-07, Klaus Kragelund <klauskvik@hotmail.com> wrote:

Hi

I have a prototype setup where I need to turn a 145 degree intensity field from a LED into a parallel field

pull a lens from one of theose $3 flashlights, they can project an image of the die on the wall.

> There is no readily available lenses so I was thinking about 3D printing PLA to make a custom reflector

then what?

> But then I need reflective paint. What can I use, a chrome paint or?

you pretty much have to use metal to make a mirror.

If you have a vacuum chamber you can deposit aluminium, if not there's
a chemical silver process.

--
Jasen.

 

[Phil Hobbs]

On 2020-02-07 15:37, John Larkin wrote:

On Fri, 7 Feb 2020 14:39:04 -0500, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 2020-02-07 14:26, Dave Platt wrote:
In article <d0dfbdd7-6d0d-4a36-a526-05ca49283a1c@googlegroups.com>,
Klaus Kragelund <klauskvik@hotmail.com> wrote:
Hi

I have a prototype setup where I need to turn a 145 degree intensity field from a LED into a parallel field

There is no readily available lenses so I was thinking about 3D printing PLA to make a custom reflector

But then I need reflective paint. What can I use, a chrome paint or?

It sounds as if what you want to do, is something vaguely similar to
what Bausch & Lomb did with their "Nicholas" illuminator for their
stereo microscopes. If I recall correctly the B&L Nicholas
illuminator uses both lenses, and a reflective tube to collimate the
beam.

Any sort of paint I can think of, is going to turn your reflector
surface into a diffuser... the unevenness of the paint surface is
going to be quite a few wavelengths. You'll get a lot of light coming
off of it at angles which result in a "sort of parallel" field,
overall... that may or may not be adequate for your application. If
you just need effective illumination, maybe so... if you're expecting
sharp-edged shadows, probably not.

If you really do need a well-collimated beam, you're going to need
something approaching an optically-accurate reflective surface. To me
that suggests "smooth it carefully, buff on some graphite, and then
electroplate it". A commercial silver-plating company might be able
to deposit-and-polish.

I suspect that a lens-based approach is likely to be easier to get
working properly. Sure you can't find anything in Edmund's catalog
which could be pressed into service?


Lenses are heartbreakingly inefficient for this job, trust me. A
large-aperture paraboloid with the LED at the focus (pointing at the
mirror) is the ticket.

LEDs are spatially incoherent, and so radiate into a hemisphere (pi
steradians projected solid angle). The projected solid angle of a lens
with a given numerical aperture is pi*NA**2. (A hemisphere corresponds
to NA=1.) So the light collection efficiency of a lens is just NA**2.

A super-large aperture lens, such as 25 mm FL, 25 mm diameter, has an NA
of 0.5, meaning that it collects only a quarter of the light. It also
has horrible aberrations, so the collimated beam quality is poor. Most
lens-based condenser systems are much less efficient than that--a 100 mm
FL lens of 25 mm diameter collects only 1/64 of the light.

Cheers

Phil Hobbs

Might a Fresnel be better here?

It's really hard to make a Fresnel lens faster than NA=0.5. Higher
refractive index helps with the NA, but the Fresnel reflections get
quadratically worse.

Cheers

Phil Hobbs


--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

On Friday, February 7, 2020 at 3:41:24 PM UTC-5, John Larkin wrote:

On Fri, 7 Feb 2020 10:01:25 -0800 (PST), Klaus Kragelund
klauskvik@hotmail.com> wrote:

Hi

I have a prototype setup where I need to turn a 145 degree intensity field from a LED into a parallel field

There is no readily available lenses so I was thinking about 3D printing PLA to make a custom reflector

But then I need reflective paint. What can I use, a chrome paint or?

Cheers

Klaus

3D printing is slow and makes gritty surfaces.

Maybe press aluminum foil into a mold?

Vacuum forming can be cool. I wonder if you could vac form aluminized
plastic.

There's probably a suitable cheap reflector already available
somewhere. Maybe in a car tail-light or something.



--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

Agree 3D printing using FDM is coarse, stereo lithography is much smoother and has post processing options. Check out Shapeways.com or many other 3D prototype vendors.

 

[Klaus Kragelund]

On Friday, February 7, 2020 at 11:44:43 PM UTC+1, alan.ye...@gmail.com wrote:

On Friday, February 7, 2020 at 3:41:24 PM UTC-5, John Larkin wrote:
On Fri, 7 Feb 2020 10:01:25 -0800 (PST), Klaus Kragelund
klauskvik@hotmail.com> wrote:

Hi

I have a prototype setup where I need to turn a 145 degree intensity field from a LED into a parallel field

There is no readily available lenses so I was thinking about 3D printing PLA to make a custom reflector

But then I need reflective paint. What can I use, a chrome paint or?

Cheers

Klaus

3D printing is slow and makes gritty surfaces.

Maybe press aluminum foil into a mold?

Vacuum forming can be cool. I wonder if you could vac form aluminized
plastic.

There's probably a suitable cheap reflector already available
somewhere. Maybe in a car tail-light or something.



--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

Agree 3D printing using FDM is coarse, stereo lithography is much smoother and has post processing options. Check out Shapeways.com or many other 3D prototype vendors.

We have 100k dollar 3D printers in our facility, so we do not have problems with coarse surfaces. Cheaper machines for simple prototypes outputs samples that can be sanded lightly to provide smooth surfaces

Cheers

Klaus

 

[Mikko OH2HVJ]

Klaus Kragelund <klauskvik@hotmail.com> writes:

Hi

I have a prototype setup where I need to turn a 145 degree intensity field from a LED into a parallel field

There is no readily available lenses so I was thinking about 3D printing PLA to make a custom reflector

Have you checked www.ledil.com ? The selection is huge and many are
available from they usual suspects. They've got both lenses and
reflectors and the search engine is quite nice.

--
mikko

 

[whit3rd]

On Friday, February 7, 2020 at 10:01:34 AM UTC-8, Klaus Kragelund wrote:

Hi

I have a prototype setup where I need to turn a 145 degree intensity field from a LED into a parallel field

There is no readily available lenses so I was thinking about 3D printing PLA to make a custom reflector

Huh? Hit up a thrift store, get any old point-and-shoot film camera, and plop the LED into the
middle of the focal plane where the film used to go. It might not capture all the light, but
from anything similar to a point source, it'll give you collimation.

Or if you want a wider beam, toys like this
<https://www.amazon.com/Discovery-Projector-Walls-Ceiling-Markers/dp/B077VYGHYZ/ref=sr_1_16>
are basically an LED, a Fresnel collimating lens, and a projection lens to focus the image
of a transparency onto the ceiling.

 

[Martin Brown]

On 07/02/2020 18:01, Klaus Kragelund wrote:

Hi

I have a prototype setup where I need to turn a 145 degree intensity field from a LED into a parallel field

There is no readily available lenses so I was thinking about 3D printing PLA to make a custom reflector

Your best bet for a lens is one off those cheap LED torches which will
almost generate a parallel beam image of the chip. Approx 15mm diameter.

Take the lens off something like this one (other brands are available).

https://www.ebay.co.uk/itm/Police-20000LM-T6-LED-18650-Super-Bright-Zoom-Flashlight-Powerful-Lamp-Torches/143469769858

The one I have is almost good enough collimation to point at stars with.
You could certainly point at a whole constellations.

--
Regards,
Martin Brown

 

[Martin Brown]

On 07/02/2020 19:39, Phil Hobbs wrote:

On 2020-02-07 14:26, Dave Platt wrote:
In article <d0dfbdd7-6d0d-4a36-a526-05ca49283a1c@googlegroups.com>,
Klaus Kragelund  <klauskvik@hotmail.com> wrote:
Hi

I have a prototype setup where I need to turn a 145 degree intensity
field from a LED into a parallel field

Wouldn't it be easier to start with an LED that emits a tighter beam?

That is with the light output already roughly collimated by the shape of
the water clear plastic on top of the die. You can get tiny reflectors
that fit around certain designs of power LED - modifying one of them to
fit your particular device might be easier than starting from scratch.

There is no readily available lenses so I was thinking about 3D
printing PLA to make a custom reflector

But then I need reflective paint. What can I use, a chrome paint or?

It sounds as if what you want to do, is something vaguely similar to
what Bausch & Lomb did with their "Nicholas" illuminator for their
stereo microscopes.  If I recall correctly the B&L Nicholas
illuminator uses both lenses, and a reflective tube to collimate the
beam.

Any sort of paint I can think of, is going to turn your reflector
surface into a diffuser... the unevenness of the paint surface is
going to be quite a few wavelengths.  You'll get a lot of light coming
off of it at angles which result in a "sort of parallel" field,
overall... that may or may not be adequate for your application.  If
you just need effective illumination, maybe so... if you're expecting
sharp-edged shadows, probably not.

If you really do need a well-collimated beam, you're going to need
something approaching an optically-accurate reflective surface.  To me
that suggests "smooth it carefully, buff on some graphite, and then
electroplate it".  A commercial silver-plating company might be able
to deposit-and-polish.

If it is a one off then classic wet silver deposition chemistry isn't
too hard and will give an optical quality finish if the original surface
is suitably polished. Old amateur telescope books have the method.

I suspect that a lens-based approach is likely to be easier to get
working properly.  Sure you can't find anything in Edmund's catalog
which could be pressed into service?


Lenses are heartbreakingly inefficient for this job, trust me.  A
large-aperture paraboloid with the LED at the focus (pointing at the
mirror) is the ticket.

Yes but even then you are up against the finite size of the die.

Doing something clever at the receptor end to capture as much of the
incident light as possible might be more rewarding.

LEDs are spatially incoherent, and so radiate into a hemisphere (pi
steradians projected solid angle).  The projected solid angle of a lens
with a given numerical aperture is pi*NA**2. (A hemisphere corresponds
to NA=1.)  So the light collection efficiency of a lens is just NA**2.

A super-large aperture lens, such as 25 mm FL, 25 mm diameter, has an NA
of 0.5, meaning that it collects only a quarter of the light.  It also
has horrible aberrations, so the collimated beam quality is poor.  Most
lens-based condenser systems are much less efficient than that--a 100 mm
FL lens of 25 mm diameter collects only 1/64 of the light.

The 15mm diameter cast aspheric lenses on the cheapo LED torches don't
do too badly at collimating a parallel beam from a power LED. I grant
you that maybe half the light output isn't in the beam itself but it is
pretty good and you can project an image of the LED die onto clouds.

A decent monochromatic laser with lens collimation is way better.

The OP's requirements are ultimately up against laws of thermodynamics.

--
Regards,
Martin Brown

 

[Phil Hobbs]

On 2020-02-10 04:17, Martin Brown wrote:

On 07/02/2020 19:39, Phil Hobbs wrote:
On 2020-02-07 14:26, Dave Platt wrote:
In article <d0dfbdd7-6d0d-4a36-a526-05ca49283a1c@googlegroups.com>,
Klaus Kragelund  <klauskvik@hotmail.com> wrote:
Hi

I have a prototype setup where I need to turn a 145 degree intensity
field from a LED into a parallel field

Wouldn't it be easier to start with an LED that emits a tighter beam?

That is with the light output already roughly collimated by the shape of
the water clear plastic on top of the die. You can get tiny reflectors
that fit around certain designs of power LED - modifying one of them to
fit your particular device might be easier than starting from scratch.

There is no readily available lenses so I was thinking about 3D
printing PLA to make a custom reflector

But then I need reflective paint. What can I use, a chrome paint or?

It sounds as if what you want to do, is something vaguely similar to
what Bausch & Lomb did with their "Nicholas" illuminator for their
stereo microscopes.  If I recall correctly the B&L Nicholas
illuminator uses both lenses, and a reflective tube to collimate the
beam.

Any sort of paint I can think of, is going to turn your reflector
surface into a diffuser... the unevenness of the paint surface is
going to be quite a few wavelengths.  You'll get a lot of light coming
off of it at angles which result in a "sort of parallel" field,
overall... that may or may not be adequate for your application.  If
you just need effective illumination, maybe so... if you're expecting
sharp-edged shadows, probably not.

If you really do need a well-collimated beam, you're going to need
something approaching an optically-accurate reflective surface.  To me
that suggests "smooth it carefully, buff on some graphite, and then
electroplate it".  A commercial silver-plating company might be able
to deposit-and-polish.

If it is a one off then classic wet silver deposition chemistry isn't
too hard and will give an optical quality finish if the original surface
is suitably polished. Old amateur telescope books have the method.

I suspect that a lens-based approach is likely to be easier to get
working properly.  Sure you can't find anything in Edmund's catalog
which could be pressed into service?


Lenses are heartbreakingly inefficient for this job, trust me.  A
large-aperture paraboloid with the LED at the focus (pointing at the
mirror) is the ticket.

Yes but even then you are up against the finite size of the die.

You can't make a perfectly collimated beam from a LED, but good ones are
brighter than most thermal sources, so it isn't a bad place to start.

Doing something clever at the receptor end to capture as much of the
incident light as possible might be more rewarding.

LEDs are spatially incoherent, and so radiate into a hemisphere (pi
steradians projected solid angle).  The projected solid angle of a
lens with a given numerical aperture is pi*NA**2. (A hemisphere
corresponds to NA=1.)  So the light collection efficiency of a lens is
just NA**2.

A super-large aperture lens, such as 25 mm FL, 25 mm diameter, has an
NA of 0.5, meaning that it collects only a quarter of the light.  It
also has horrible aberrations, so the collimated beam quality is
poor.  Most lens-based condenser systems are much less efficient than
that--a 100 mm FL lens of 25 mm diameter collects only 1/64 of the light.

The 15mm diameter cast aspheric lenses on the cheapo LED torches don't
do too badly at collimating a parallel beam from a power LED. I grant
you that maybe half the light output isn't in the beam itself but it is
pretty good and you can project an image of the LED die onto clouds.

"pretty good" isn't too quantitative.

A decent monochromatic laser with lens collimation is way better.

Sure, because its phase space volume is a single mode. Much much easier.

The OP's requirements are ultimately up against laws of thermodynamics.

Yes, but the arguments are a bit subtler there since a LED is not
exactly a thermal source.

Cheers

Phil Hobbs



--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com