entendu confusion

[b***@4dtechnology.com]

Hello,

I have a high brightness LED that is approximately Lambertian with a
1.5mm source size radius. My object space NA is .25, this obviously
limits the amount of light I can get into my system.

I can get a concentrating optic that turns the +/-90 deg output of the
LED to about a +/- 10 degree output.

This is great but here is my confusion. Normally I would say you can
not get an increase in the amount of light in the system without
increasing the system NA, since you can not increase the radiance.

Shouldn't the apparent source size now increase since the source
divergence has decreased?

I'm sure I am thinking about this incorrectly.

Any clarification on this matter would be appreciated.

Brad

[Salmon Egg]

In article

Post by b***@4dtechnology.com
Hello,
I have a high brightness LED that is approximately Lambertian with a
1.5mm source size radius. My object space NA is .25, this obviously
limits the amount of light I can get into my system.
I can get a concentrating optic that turns the +/-90 deg output of the
LED to about a +/- 10 degree output.
This is great but here is my confusion. Normally I would say you can
not get an increase in the amount of light in the system without
increasing the system NA, since you can not increase the radiance.
Shouldn't the apparent source size now increase since the source
divergence has decreased?
I'm sure I am thinking about this incorrectly.
Any clarification on this matter would be appreciated.
Brad

It depends upon how you are using the light. For example, if the point
is to carry out a simple photochemical reaction, it will be the total
absorbed energy that counts rather than anything that depends upon
radiance directly.

Bill

[Phil Hobbs]

Post by Salmon Egg
In article

Post by b***@4dtechnology.com
Hello,
I have a high brightness LED that is approximately Lambertian with a
1.5mm source size radius. My object space NA is .25, this obviously
limits the amount of light I can get into my system.
I can get a concentrating optic that turns the +/-90 deg output of the
LED to about a +/- 10 degree output.
This is great but here is my confusion. Normally I would say you can
not get an increase in the amount of light in the system without
increasing the system NA, since you can not increase the radiance.
Shouldn't the apparent source size now increase since the source
divergence has decreased?
I'm sure I am thinking about this incorrectly.
Any clarification on this matter would be appreciated.
Brad

It depends upon how you are using the light. For example, if the point
is to carry out a simple photochemical reaction, it will be the total
absorbed energy that counts rather than anything that depends upon
radiance directly.
Bill

You still can't increase the radiance of a thermal (or other completely
incoherent) source. If the concentrator has high efficiency, it will
increase the apparent area of the source. Otherwise you could use it to
build a perpetual motion machine.

Cheers

Phil Hobbs

[Salmon Egg]

Post by Phil Hobbs

Post by Salmon Egg
It depends upon how you are using the light. For example, if the point
is to carry out a simple photochemical reaction, it will be the total
absorbed energy that counts rather than anything that depends upon
radiance directly.
Bill

You still can't increase the radiance of a thermal (or other completely
incoherent) source. If the concentrator has high efficiency, it will
increase the apparent area of the source. Otherwise you could use it to
build a perpetual motion machine.

Large numerical aperture can help increase the transfer efficiency of
light. But once the light enters and gets absorbed the reaction chamber
mentioned above, the original radiance level is of no consequence.

Bill

[Phil Hobbs]

Post by Salmon Egg

Post by Phil Hobbs

Post by Salmon Egg
It depends upon how you are using the light. For example, if the point
is to carry out a simple photochemical reaction, it will be the total
absorbed energy that counts rather than anything that depends upon
radiance directly.
Bill

You still can't increase the radiance of a thermal (or other completely
incoherent) source. If the concentrator has high efficiency, it will
increase the apparent area of the source. Otherwise you could use it to
build a perpetual motion machine.

Large numerical aperture can help increase the transfer efficiency of
light. But once the light enters and gets absorbed the reaction chamber
mentioned above, the original radiance level is of no consequence.
Bill

Maybe sometimes, but not so in general...there's often an important
difference between increasing the local irradiance and increasing the
irradiated area.

Cheers

Phil Hobbs

[Salmon Egg]

Post by Phil Hobbs

Post by Salmon Egg
Large numerical aperture can help increase the transfer efficiency of
light. But once the light enters and gets absorbed the reaction chamber
mentioned above, the original radiance level is of no consequence.
Bill

Maybe sometimes, but not so in general...there's often an important
difference between increasing the local irradiance and increasing the
irradiated area.

I did mention simple chemical reactions. There can be nonlinear effects
or multiphoton effects. I doubt that it makes much about curing of
optical cement by ultraviolet radiation that depends upon radiance
rather than total absorbed energy. The same applies to silver
photography over the range of reciprocity. Exposure would be much more
complicated if you did not depend upon the total number of photons
absorbed by a silver halide crystal.

Bill

[s***@lw4u.com]

Post by b***@4dtechnology.com
Shouldn't the apparent source size now increase since the source
divergence has decreased?

Correct.

Spencer
========================
LIGHT WORKS, LLC
http://www.LW4U.com

[Boxman]

Post by b***@4dtechnology.com
Hello,
I have a high brightness LED that is approximately Lambertian with a
1.5mm source size radius.  My object space NA is .25, this obviously
limits the amount of light I can get into my system.
I can get a concentrating optic that turns the +/-90 deg output of the
LED to about a +/- 10 degree output.
This is great but here is my confusion.  Normally I would say you can
not get an increase in the amount of light in the system without
increasing the system NA, since you can not increase the radiance.
Shouldn't the apparent source size now increase since the source
divergence has decreased?
I'm sure I am thinking about this incorrectly.
Any clarification on this matter would be appreciated.
Brad

If you look at just the concentrating optic system - If it is designed
to match the etendue of the LED (i.e. most efficient transfer) then
the diameter of the optic won't be any smaller than what the 2D
etendue equation would require.

In your example, the etendue of your source is area source*solid angle
which will be pi*1.5^2 (area)*pi(solid angle for lambertian) = 22.184
sr/mm^2. The etendue of the concentrating optic if designed for
optimium transfer would be equal (or greater than) the source. The
solid angle from your concentrating optic is pi*sin^2(theta) where
theta is half angle or in your case =0.09 sr. The area of your
concentrating optic would then have to be 246 mm^2 or have a radius
of about 9 mm or overall diameter of 18 mm to have equal etendue, thus
assuring highest transfer efficiency.

In that case then, the etendue of your concentrated optic is still the
same as the etendue of your original source, but your source area at
the exit of the concentrator optic has increased while your solid
angle decreased. The theoretical collection into your 0.25NA system
won't have changed.

[Clo-Clo]

<***@4dtechnology.com> wrote

snip snip snip

You just got learned answers from respected experts.

But you really meant "étendue confusion", note spelling.

[Helpful person]

Post by b***@4dtechnology.com
Hello,
I have a high brightness LED that is approximately Lambertian with a
1.5mm source size radius.  My object space NA is .25, this obviously
limits the amount of light I can get into my system.
I can get a concentrating optic that turns the +/-90 deg output of the
LED to about a +/- 10 degree output.
This is great but here is my confusion.  Normally I would say you can
not get an increase in the amount of light in the system without
increasing the system NA, since you can not increase the radiance.
Shouldn't the apparent source size now increase since the source
divergence has decreased?
I'm sure I am thinking about this incorrectly.
Any clarification on this matter would be appreciated.
Brad

As Spencer said you are exactly correct. Reducing the NA increases
the apparent source size by the same ratio. Don't get confused by
other irrelevent discussions.

www.richardfisher.com

[Richard J Kinch]

Post by b***@4dtechnology.com
This is great but here is my confusion. Normally I would say you can
not get an increase in the amount of light in the system without
increasing the system NA, since you can not increase the radiance.

Does the "concentrating optic" alter the NA?

[Bob May]

Ultimately.

--
Bob May

rmay at nethere.com
http: slash /nav.to slash bobmay
http: slash /bobmay dot astronomy.net