sphere standards and standard spheres dr. richard young optronic laboratories, inc

Optronic Laboratories, Inc.Optronic Laboratories, Inc.

Sphere Standards and Sphere Standards and Standard SpheresStandard Spheres


Dr. Richard YoungDr. Richard Young





Sphere ApplicationsSphere ApplicationsSphere ApplicationsSphere ApplicationsStandard SpheresStandard Spheres

Total flux measurementsTotal flux measurements• All the light from a lamp is measured

Irradiance measurementsIrradiance measurements• Light at a surface is measured

Sphere standardsSphere standards Large uniform source is used for Large uniform source is used for

calibration of instrumentscalibration of instruments

Standard SpheresStandard Spheres Total flux measurementsTotal flux measurements

• All the light from a lamp is measured

Irradiance measurementsIrradiance measurements• Light at a surface is measured

Sphere standardsSphere standards Large uniform source is used for Large uniform source is used for

calibration of instrumentscalibration of instruments


Total FluxTotal FluxTotal FluxTotal FluxAn integrating sphere has several An integrating sphere has several

interesting properties:interesting properties: Any part of the sphere surface “sees” all Any part of the sphere surface “sees” all

other parts of the sphere surface equally.other parts of the sphere surface equally.• This means a detector at any point on the

surface can measure the total power in the entire sphere.

Reflections from the sphere wall add to Reflections from the sphere wall add to the lamp power, giving more power the lamp power, giving more power inside the sphere than the lamp is inside the sphere than the lamp is generating.generating.

An integrating sphere has several An integrating sphere has several interesting properties:interesting properties: Any part of the sphere surface “sees” all Any part of the sphere surface “sees” all

other parts of the sphere surface equally.other parts of the sphere surface equally.• This means a detector at any point on the

surface can measure the total power in the entire sphere.

Reflections from the sphere wall add to Reflections from the sphere wall add to the lamp power, giving more power the lamp power, giving more power inside the sphere than the lamp is inside the sphere than the lamp is generating.generating.


Total FluxTotal FluxTotal FluxTotal Flux The lamp is placed The lamp is placed

in the center.in the center. A baffle prevents A baffle prevents

direct light hitting direct light hitting the detector.the detector.

The sphere walls The sphere walls and baffle are and baffle are highly reflective.highly reflective.

The lamp is placed The lamp is placed in the center.in the center.

A baffle prevents A baffle prevents direct light hitting direct light hitting the detector.the detector.

The sphere walls The sphere walls and baffle are and baffle are highly reflective.highly reflective.

LampLamp

BaffleBaffle

DetectorDetector


Total FluxTotal FluxTotal FluxTotal Flux Light from the Light from the

lamp hits the lamp hits the sphere wall equally sphere wall equally in almost all in almost all directions…directions…

Light from the Light from the lamp hits the lamp hits the sphere wall equally sphere wall equally in almost all in almost all directions…directions…


Total FluxTotal FluxTotal FluxTotal Flux Light from the Light from the

lamp hits the lamp hits the sphere wall equally sphere wall equally in almost all in almost all directions…directions…

But there are But there are variations in variations in sphere response.sphere response.

Light from the Light from the lamp hits the lamp hits the sphere wall equally sphere wall equally in almost all in almost all directions…directions…

But there are But there are variations in variations in sphere response.sphere response.

Shadow area

Shadow area

Partial Shadow area

Partial Shadow area


Total FluxTotal FluxTotal FluxTotal Flux In these shadow In these shadow

areas, the “first areas, the “first strike” strike” (light (light directly from the directly from the lamp)lamp) is not fully is not fully measured.measured.

A sphere cannot A sphere cannot have PERFECT have PERFECT response.response.

In these shadow In these shadow areas, the “first areas, the “first strike” strike” (light (light directly from the directly from the lamp)lamp) is not fully is not fully measured.measured.

A sphere cannot A sphere cannot have PERFECT have PERFECT response.response.

Shadow area

Shadow area

Partial Shadow area

Partial Shadow area


Total FluxTotal FluxTotal FluxTotal FluxAlthough perfect response is not Although perfect response is not

attainable with this design, practical attainable with this design, practical spheres can come very close.spheres can come very close.

How close they come depends on How close they come depends on attention to small details of design.attention to small details of design.

Although perfect response is not Although perfect response is not attainable with this design, practical attainable with this design, practical spheres can come very close.spheres can come very close.

How close they come depends on How close they come depends on attention to small details of design.attention to small details of design.

“An expert is someone who knows some of the worst mistakes that can be made in his subject

and how to avoid them.” - W. Heisenberg

“An expert is someone who knows some of the worst mistakes that can be made in his subject

and how to avoid them.” - W. Heisenberg


Total FluxTotal FluxTotal FluxTotal Flux Response is best Response is best

viewed on a radar viewed on a radar graph.graph.

Response varies Response varies with sphere size with sphere size and reflectivity.and reflectivity.

If a reflectivity of If a reflectivity of 95% is used… 95% is used…

Response is best Response is best viewed on a radar viewed on a radar graph.graph.



0

0.2

0.4

0.6

0.8

1

0.5 m sphere0.5 m sphere









0

0.2

0.4

0.6

0.8

1



Total FluxTotal FluxTotal FluxTotal Flux A reflectivity of A reflectivity of

98% or more is 98% or more is more common for more common for US manufactured US manufactured spheres.spheres.

A reflectivity of A reflectivity of 98% or more is 98% or more is more common for more common for US manufactured US manufactured spheres.spheres.

0

0.2

0.4

0.6

0.8

1


Total FluxTotal FluxTotal FluxTotal Flux Some European Some European

standards standards recommend 80% recommend 80% reflectivity.reflectivity.

But this gives large But this gives large geometric errors.geometric errors.

Some European Some European standards standards recommend 80% recommend 80% reflectivity.reflectivity.

But this gives large But this gives large geometric errors.geometric errors.0

0.2

0.4

0.6

0.8

1

Note the higher response in placesNote the higher

response in places


Total FluxTotal FluxTotal FluxTotal Flux This high response This high response

is caused by is caused by reflections from reflections from the detector side of the detector side of the baffle.the baffle.

This high response This high response is caused by is caused by reflections from reflections from the detector side of the detector side of the baffle.the baffle.


Total FluxTotal FluxTotal FluxTotal Flux This high response This high response

is caused by is caused by reflections from reflections from the detector side of the detector side of the baffle.the baffle.

It is present in all It is present in all spheres, but some spheres, but some are much worse are much worse than others.than others.

This high response This high response is caused by is caused by reflections from reflections from the detector side of the detector side of the baffle.the baffle.

It is present in all It is present in all spheres, but some spheres, but some are much worse are much worse than others.than others.


Total FluxTotal FluxTotal FluxTotal Flux All the prior sphere All the prior sphere

responses had one responses had one thing in common:thing in common: The detector had a The detector had a

cosine collector on cosine collector on it.it.

If we remove the If we remove the cosine collector…cosine collector…

All the prior sphere All the prior sphere responses had one responses had one thing in common:thing in common: The detector had a The detector had a

cosine collector on cosine collector on it.it.

If we remove the If we remove the cosine collector…cosine collector…

Radial Response Map

0.0

0.2

0.4

0.6

0.8

1.0

1.21

2 3 45 6 7

89 1 01 1 1 2

1 31 4 1 5

1 61 7

1 81 9

2 02 1

2 2

2 32 42 5

2 6

2 72 8

2 9

3 03 1

3 2

3 3

3 43 5

3 6

3 7

3 83 9

4 0

4 1

4 2

4 3

4 4

4 5

4 6

4 7

4 8

4 9

5 0

5 1

5 25 3

5 4

5 5

5 6

5 7

5 8

5 9

6 0

6 1

6 2

6 3

6 4

6 5

6 6

6 76 8

6 9

7 0

7 1

7 2

7 3

7 4

7 5

7 6

7 7

7 8

7 9

8 0

8 1

8 28 3

8 4

8 5

8 6

8 7

8 8

8 9

9 0

9 1

9 2

9 3

9 4

9 5

9 6

9 79 8

9 9

1 0 0

1 0 1

1 0 2

1 0 3

1 0 4

1 0 5

1 0 6

1 0 7

1 0 8

1 0 9

1 1 0

1 1 1

1 1 21 1 3

1 1 4

1 1 5

1 1 6

1 1 7

1 1 8

1 1 9

1 2 0

1 2 1

1 2 2

1 2 3

1 2 4

1 2 5

1 2 6

1 2 71 2 8

1 2 9

1 3 0

1 3 1

1 3 2

1 3 3

1 3 4

1 3 5

1 3 6

1 3 7

1 3 8

1 3 9

1 4 0

1 4 1

1 4 21 4 3

1 4 4

1 4 5

1 4 6

1 4 7

1 4 8

1 4 9

1 5 0

1 5 1

1 5 2

1 5 3

1 5 4

1 5 5

1 5 61 5 7

1 5 8

1 5 9

1 6 01 6 1

1 6 2

1 6 3

1 6 41 6 5

1 6 6

1 6 71 6 8

1 6 91 7 0

1 7 11 7 2

1 7 31 7 4

1 7 51 7 6

1 7 71 7 8

1 7 91 8 01 8 1

1 8 21 8 31 8 4

1 8 51 8 61 8 71 8 81 8 91 9 0

1 9 11 9 21 9 3

1 9 4

1 9 51 9 61 9 71 9 81 9 92 0 0

2 0 12 0 22 0 32 0 42 0 5

2 0 62 0 72 0 8

2 0 92 1 0

2 1 12 1 2

2 1 32 1 4

2 1 5

2 1 62 1 72 1 8

2 1 9

2 2 02 2 1

2 2 2

2 2 32 2 4

2 2 5

2 2 6

2 2 72 2 8

2 2 9

2 3 0

2 3 12 3 2

2 3 3

2 3 4

2 3 5

2 3 6

2 3 7

2 3 8

2 3 9

2 4 0

2 4 1

2 4 2

2 4 3

2 4 4

2 4 52 4 6

2 4 7

2 4 8

2 4 9

2 5 0

2 5 1

2 5 2

2 5 3

2 5 4

2 5 5

2 5 6

2 5 7

2 5 8

2 5 9

2 6 02 6 1

2 6 2

2 6 3

2 6 4

2 6 5

2 6 6

2 6 7

2 6 8

2 6 9

2 7 0

2 7 1

2 7 2

2 7 3

2 7 4

2 7 52 7 6

2 7 7

2 7 8

2 7 9

2 8 0

2 8 1

2 8 2

2 8 3

2 8 4

2 8 5

2 8 6

2 8 7

2 8 8

2 8 9

2 9 02 9 1

2 9 2

2 9 3

2 9 4

2 9 5

2 9 6

2 9 7

2 9 8

2 9 9

3 0 0

3 0 1

3 0 2

3 0 3

3 0 4

3 0 53 0 6

3 0 7

3 0 8

3 0 9

3 1 0

3 1 1

3 1 2

3 1 3

3 1 4

3 1 5

3 1 6

3 1 7

3 1 8

3 1 9

3 2 03 2 1

3 2 2

3 2 3

3 2 4

3 2 5

3 2 6

3 2 7

3 2 8

3 2 9

3 3 0

3 3 1

3 3 2

3 3 3

3 3 4

3 3 53 3 6

3 3 7

3 3 8

3 3 9

3 4 0

3 4 1

3 4 2

3 4 3

3 4 4

3 4 5

3 4 6

3 4 7

3 4 8

3 4 93 5 0

3 5 1

3 5 2

3 5 33 5 4

3 5 5

3 5 6

3 5 73 5 8

3 5 9

3 6 03 6 1

3 6 23 6 3

3 6 43 6 5

3 6 63 6 7

3 6 83 6 9

3 7 03 7 1

3 7 23 7 33 7 4

3 7 53 7 63 7 7

3 7 83 7 93 8 03 8 1 3 8 23 8 3

3 8 43 8 53 8 6

Cosine collectorremoved

EquatorialAngle

The response of The response of even the best even the best sphere is destroyedsphere is destroyed


Total FluxTotal FluxTotal FluxTotal FluxMany Sources are highly directionalMany Sources are highly directionalMany Sources are highly directionalMany Sources are highly directional

Fluorescent LampsFluorescent Lamps


Total FluxTotal FluxTotal FluxTotal FluxMany Sources are highly directionalMany Sources are highly directionalMany Sources are highly directionalMany Sources are highly directional

LEDsLEDs


Total FluxTotal FluxTotal FluxTotal Flux A sphere has areas A sphere has areas

of uniform of uniform response (green).response (green).

And non-uniform And non-uniform areas (red).areas (red).

If the source is If the source is highly directional, highly directional, it should be it should be pointed at a green pointed at a green area for the best area for the best results.results.

A sphere has areas A sphere has areas of uniform of uniform response (green).response (green).

And non-uniform And non-uniform areas (red).areas (red).

If the source is If the source is highly directional, highly directional, it should be it should be pointed at a green pointed at a green area for the best area for the best results.results.


Total FluxTotal FluxTotal FluxTotal Flux The green area is The green area is

bigger for larger bigger for larger spheres.spheres.

The red area is The red area is bigger for larger bigger for larger baffles.baffles.

The green area is The green area is bigger for larger bigger for larger spheres.spheres.

The red area is The red area is bigger for larger bigger for larger baffles.baffles.


Total FluxTotal FluxTotal FluxTotal FluxGeometrically, the highest Geometrically, the highest

accuracies are obtained by orienting accuracies are obtained by orienting lamps so the maximum output is lamps so the maximum output is directed at areas of uniform directed at areas of uniform response.response.

Highly reflective coatings give much Highly reflective coatings give much lower geometrical errors, regardless lower geometrical errors, regardless of orientation, than less reflective of orientation, than less reflective coatings.coatings.

Geometrically, the highest Geometrically, the highest accuracies are obtained by orienting accuracies are obtained by orienting lamps so the maximum output is lamps so the maximum output is directed at areas of uniform directed at areas of uniform response.response.

Highly reflective coatings give much Highly reflective coatings give much lower geometrical errors, regardless lower geometrical errors, regardless of orientation, than less reflective of orientation, than less reflective coatings.coatings.


Total FluxTotal FluxTotal FluxTotal FluxHowever,However,Anything placed inside spheres, Anything placed inside spheres,

including lamps, holders, sockets including lamps, holders, sockets and cables, can absorb light and and cables, can absorb light and change the sphere throughput.change the sphere throughput.

The higher the reflectivity of the The higher the reflectivity of the sphere, the bigger the change to sphere, the bigger the change to throughput when something is throughput when something is placed inside.placed inside.

However,However,Anything placed inside spheres, Anything placed inside spheres,

including lamps, holders, sockets including lamps, holders, sockets and cables, can absorb light and and cables, can absorb light and change the sphere throughput.change the sphere throughput.

The higher the reflectivity of the The higher the reflectivity of the sphere, the bigger the change to sphere, the bigger the change to throughput when something is throughput when something is placed inside.placed inside.


Total FluxTotal FluxTotal FluxTotal Flux

0.01%

0.10%

1.00%

10.00%

100.00%

0.00001% 0.0001% 0.001% 0.01% 0.1%

Object in Sphere as % of Sphere Volume

% C

han

ge

in S

ph

ere

Th

rou

gh

pu

t

99%

98%

97%

95%

90%

80%

CoatingReflectivity

Here, the effective reflectivity is changed by just 0.25%

Here, the effective reflectivity is changed by just 0.25%


Total FluxTotal FluxTotal FluxTotal FluxThis example is for a black spherical This example is for a black spherical

object in the center of the sphere.object in the center of the sphere.Actual changes will depend on the Actual changes will depend on the

object’s reflectance, shape and object’s reflectance, shape and position in the sphere, and can be position in the sphere, and can be larger than shown.larger than shown.

This example is for a black spherical This example is for a black spherical object in the center of the sphere.object in the center of the sphere.

Actual changes will depend on the Actual changes will depend on the object’s reflectance, shape and object’s reflectance, shape and position in the sphere, and can be position in the sphere, and can be larger than shown.larger than shown.


Total FluxTotal FluxTotal FluxTotal FluxThe lamp used in calibration and the The lamp used in calibration and the

lamp to be measured are rarely the lamp to be measured are rarely the same.same.

Different changes in throughput Different changes in throughput between these lamps will mean between these lamps will mean results will be wrong unless results will be wrong unless throughput changes are also throughput changes are also measured.measured.

The lamp used in calibration and the The lamp used in calibration and the lamp to be measured are rarely the lamp to be measured are rarely the same.same.

Different changes in throughput Different changes in throughput between these lamps will mean between these lamps will mean results will be wrong unless results will be wrong unless throughput changes are also throughput changes are also measured.measured.


Total FluxTotal FluxTotal FluxTotal Flux An auxiliary lamp, An auxiliary lamp,

which is housed which is housed permanently in the permanently in the sphere, is used to sphere, is used to measure changes measure changes in throughput.in throughput.

An auxiliary lamp, An auxiliary lamp, which is housed which is housed permanently in the permanently in the sphere, is used to sphere, is used to measure changes measure changes in throughput.in throughput.

Auxiliary Lamp

Auxiliary Lamp


Total FluxTotal FluxTotal FluxTotal Flux The auxiliary lamp The auxiliary lamp

is powered up is powered up while the standard while the standard or test lamp is in or test lamp is in the sphere.the sphere. But not switched But not switched

on.on. The ratio of signals The ratio of signals

is the change in is the change in throughput.throughput. This is part of the This is part of the

calibration calibration procedure.procedure.

The auxiliary lamp The auxiliary lamp is powered up is powered up while the standard while the standard or test lamp is in or test lamp is in the sphere.the sphere. But not switched But not switched

on.on. The ratio of signals The ratio of signals

is the change in is the change in throughput.throughput. This is part of the This is part of the

calibration calibration procedure.procedure.

Auxiliary Lamp

Auxiliary Lamp


Total FluxTotal FluxTotal FluxTotal FluxGood total flux measurements Good total flux measurements

require:require: A large high reflectivity sphere.A large high reflectivity sphere. Small, well designed, baffles.Small, well designed, baffles. A cosine collection detector at the A cosine collection detector at the

sphere wall.sphere wall. An auxiliary lamp.An auxiliary lamp.

Good total flux measurements Good total flux measurements require:require: A large high reflectivity sphere.A large high reflectivity sphere. Small, well designed, baffles.Small, well designed, baffles. A cosine collection detector at the A cosine collection detector at the

sphere wall.sphere wall. An auxiliary lamp.An auxiliary lamp.


Total FluxTotal FluxTotal FluxTotal Flux It also helps to have:It also helps to have:

Uniform measurement procedures.Uniform measurement procedures.• e.g. keep a constant time between

powering up a lamp and measuring it.

Dedicated software to guide the user Dedicated software to guide the user through calibration and through calibration and measurement.measurement.

Accurate power supplies for lamps.Accurate power supplies for lamps. NIST traceable calibration lamps.NIST traceable calibration lamps. ““Heisenberg” experts for support.Heisenberg” experts for support.

It also helps to have:It also helps to have: Uniform measurement procedures.Uniform measurement procedures.

• e.g. keep a constant time between powering up a lamp and measuring it.

Dedicated software to guide the user Dedicated software to guide the user through calibration and through calibration and measurement.measurement.

Accurate power supplies for lamps.Accurate power supplies for lamps. NIST traceable calibration lamps.NIST traceable calibration lamps. ““Heisenberg” experts for support.Heisenberg” experts for support.


IrradianceIrradianceIrradianceIrradiance Irradiance is the Irradiance is the

light flux falling light flux falling onto a surface.onto a surface.

The light can come The light can come from any direction, from any direction, and may be from and may be from multiple sources.multiple sources.

Irradiance is the Irradiance is the light flux falling light flux falling onto a surface.onto a surface.

The light can come The light can come from any direction, from any direction, and may be from and may be from multiple sources.multiple sources.

The total light The total light hitting the surface hitting the surface must be measured.must be measured.


IrradianceIrradianceIrradianceIrradiance The apparent area of a surface changes The apparent area of a surface changes

with angle.with angle. The apparent area of a surface changes The apparent area of a surface changes

with angle.with angle.

This is called the cosine law.This is called the cosine law. A measurement device that follows the A measurement device that follows the

cosine law is called a cosine collector.cosine law is called a cosine collector.

This is called the cosine law.This is called the cosine law. A measurement device that follows the A measurement device that follows the

cosine law is called a cosine collector.cosine law is called a cosine collector.


IrradianceIrradianceIrradianceIrradiance An integrating An integrating

sphere with an sphere with an input port makes input port makes an excellent cosine an excellent cosine collector…collector…

Provided certain Provided certain design rules are design rules are followed.followed.

An integrating An integrating sphere with an sphere with an input port makes input port makes an excellent cosine an excellent cosine collector…collector…

Provided certain Provided certain design rules are design rules are followed.followed.


IrradianceIrradianceIrradianceIrradiance The first rule is:The first rule is:

If light does not If light does not obey the cosine obey the cosine law when entering law when entering the sphere, there the sphere, there is little the sphere is little the sphere can do to can do to compensate.compensate.

This is easier said This is easier said than done because than done because a sphere has 2 a sphere has 2 sides – the inside sides – the inside and the outside.and the outside.

The first rule is:The first rule is: If light does not If light does not

obey the cosine obey the cosine law when entering law when entering the sphere, there the sphere, there is little the sphere is little the sphere can do to can do to compensate.compensate.


Magnify


IrradianceIrradianceIrradianceIrradiance The first rule is:The first rule is:

If light does not If light does not obey the cosine obey the cosine law when entering law when entering the sphere, there the sphere, there is little the sphere is little the sphere can do to can do to compensate.compensate.


The first rule is:The first rule is: If light does not If light does not

obey the cosine obey the cosine law when entering law when entering the sphere, there the sphere, there is little the sphere is little the sphere can do to can do to compensate.compensate.


InsideInside

OutsideOutside


IrradianceIrradianceIrradianceIrradiance This creates a This creates a

“tube” effect that “tube” effect that stops some of the stops some of the light at higher light at higher angles entering the angles entering the sphere directly.sphere directly.

This creates a This creates a “tube” effect that “tube” effect that stops some of the stops some of the light at higher light at higher angles entering the angles entering the sphere directly.sphere directly.

Some light is blocked

Some light is blocked


IrradianceIrradianceIrradianceIrradiance So, as the angle is changed, the cosine So, as the angle is changed, the cosine

response gets worse and worse.response gets worse and worse. So, as the angle is changed, the cosine So, as the angle is changed, the cosine

response gets worse and worse.response gets worse and worse.

A circle obeys the cosine lawA circle obeys the cosine law

A tube does not obey the cosine lawA tube does not obey the cosine law


IrradianceIrradianceIrradianceIrradiance The answer is The answer is

simple.simple. Make the outside Make the outside

of the sphere flat of the sphere flat to meet the inside to meet the inside at the port.at the port.

The answer is The answer is simple.simple. Make the outside Make the outside

of the sphere flat of the sphere flat to meet the inside to meet the inside at the port.at the port.

Thus eliminating Thus eliminating the “tube”.the “tube”.


IrradianceIrradianceIrradianceIrradiance So now the light So now the light

enters the sphere enters the sphere obeying the cosine obeying the cosine law.law.

So now the light So now the light enters the sphere enters the sphere obeying the cosine obeying the cosine law.law.

Rule #2: add a baffle to prevent

direct light hitting the detector

Rule #2: add a baffle to prevent

direct light hitting the detector


IrradianceIrradianceIrradianceIrradiance So now the light So now the light

enters the sphere enters the sphere obeying the cosine obeying the cosine law.law.

So now the light So now the light enters the sphere enters the sphere obeying the cosine obeying the cosine law.law.

Rule #3: the detector must also

obey the cosine law

Rule #3: the detector must also

obey the cosine law

And the sphere And the sphere can be used for can be used for irradiance irradiance measurementsmeasurements


Sphere StandardsSphere StandardsSphere StandardsSphere Standards If we replace the If we replace the

detector with a detector with a lamp, this sphere lamp, this sphere is now a source is now a source instead of a instead of a collection optic. collection optic.

If we replace the If we replace the detector with a detector with a lamp, this sphere lamp, this sphere is now a source is now a source instead of a instead of a collection optic. collection optic.


Sphere StandardsSphere StandardsSphere StandardsSphere Standards The uniformity of The uniformity of

the sphere output the sphere output depends on the depends on the way the light way the light enters the sphere.enters the sphere.

Cosine diffusers at Cosine diffusers at the input give the input give uniform output but uniform output but throw away a lot of throw away a lot of light.light.

The uniformity of The uniformity of the sphere output the sphere output depends on the depends on the way the light way the light enters the sphere.enters the sphere.

Cosine diffusers at Cosine diffusers at the input give the input give uniform output but uniform output but throw away a lot of throw away a lot of light.light.


Sphere StandardsSphere StandardsSphere StandardsSphere Standards It is difficult to It is difficult to

achieve high light achieve high light levels and good levels and good uniformity.uniformity. Especially if the Especially if the

output level also output level also needs to be needs to be variable.variable.

One option is to One option is to change the design.change the design.

It is difficult to It is difficult to achieve high light achieve high light levels and good levels and good uniformity.uniformity. Especially if the Especially if the

output level also output level also needs to be needs to be variable.variable.

One option is to One option is to change the design.change the design.


Sphere StandardsSphere StandardsSphere StandardsSphere Standards By making sure the By making sure the

input light only hits input light only hits the baffle, the the baffle, the output light is output light is randomized.randomized.

By making sure the By making sure the input light only hits input light only hits the baffle, the the baffle, the output light is output light is randomized.randomized.

If the input light If the input light level varies, so level varies, so does the output.does the output.

To track changes To track changes we add a monitor.we add a monitor.


Sphere StandardsSphere StandardsSphere StandardsSphere Standards This monitor is This monitor is

baffled so it only baffled so it only sees the output sees the output light, not the input.light, not the input.

This monitor is This monitor is baffled so it only baffled so it only sees the output sees the output light, not the input.light, not the input.

So it can be So it can be calibrated to show calibrated to show the output levels the output levels directly.directly.


Sphere StandardsSphere StandardsSphere StandardsSphere Standards The amount of The amount of

light entering the light entering the sphere can be sphere can be controlled by controlled by varying a slit.varying a slit.

The amount of The amount of light entering the light entering the sphere can be sphere can be controlled by controlled by varying a slit.varying a slit.


Sphere StandardsSphere StandardsSphere StandardsSphere Standards Non-imaging Non-imaging

collection mirrors collection mirrors can increase the can increase the light intensity.light intensity.

Non-imaging Non-imaging collection mirrors collection mirrors can increase the can increase the light intensity.light intensity.

Provided the Provided the beam is beam is approximately approximately uniform and over-uniform and over-fills the largest fills the largest slit.slit.


Sphere StandardsSphere StandardsSphere StandardsSphere StandardsSlits can be linear (1D)Slits can be linear (1D)

The width variesThe width variesOr area (2D)Or area (2D)

The width and height vary togetherThe width and height vary together

Slits can be linear (1D)Slits can be linear (1D) The width variesThe width varies

Or area (2D)Or area (2D) The width and height vary togetherThe width and height vary together


Sphere StandardsSphere StandardsSphere StandardsSphere Standards A 2D slit provides better control over a A 2D slit provides better control over a

wide range of levels than a linear (1D) slit.wide range of levels than a linear (1D) slit. A 2D slit provides better control over a A 2D slit provides better control over a

wide range of levels than a linear (1D) slit.wide range of levels than a linear (1D) slit.

1.0E-06

1.0E-05

1.0E-04

1.0E-03

1.0E-02

1.0E-01

1.0E+00

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

Normalized slit width

No

rma

lize

d o

utp

ut

1D slit 2D slit

With a 1D slit, the output drops almost vertically at small slit widths

With a 1D slit, the output drops almost vertically at small slit widths


Sphere StandardsSphere StandardsSphere StandardsSphere Standards Expressed another way, the slit resolution Expressed another way, the slit resolution

needed to change the output by 1%…needed to change the output by 1%… Expressed another way, the slit resolution Expressed another way, the slit resolution

needed to change the output by 1%…needed to change the output by 1%…

1.0E-08

1.0E-07

1.0E-06

1.0E-05

1.0E-04

1.0E-03

1.0E-02

1.0E-06 1.0E-05 1.0E-04 1.0E-03 1.0E-02 1.0E-01 1.0E+00

Normalized output

No

rma

lize

d c

ha

ng

e i

n s

lit

for

1%

ch

an

ge

in

ou

tpu

t

1D slit 2D slit

At a resolution of 10-5, the 1D slit cannot control the output below below 3 decadesAt a resolution of 10-5, the 1D slit cannot control the output below below 3 decades

2D slits can give up to 1000 times

better control than 1D slits

2D slits can give up to 1000 times

better control than 1D slits

2D slits are clearly superior for high dynamic

range sources

2D slits are clearly superior for high dynamic

range sources


Sphere StandardsSphere StandardsSphere StandardsSphere StandardsBy careful design and material selection, By careful design and material selection,

one can achieve:one can achieve: High uniformity of outputHigh uniformity of output High maximum levels of outputHigh maximum levels of output Very stable operationVery stable operation 6 or more decades of light level 6 or more decades of light level

adjustmentadjustment Direct reading of the outputDirect reading of the output Easy adjustability and setting to any levelEasy adjustability and setting to any level An almost constant spectrum at all levelsAn almost constant spectrum at all levels

By careful design and material selection, By careful design and material selection, one can achieve:one can achieve: High uniformity of outputHigh uniformity of output High maximum levels of outputHigh maximum levels of output Very stable operationVery stable operation 6 or more decades of light level 6 or more decades of light level

adjustmentadjustment Direct reading of the outputDirect reading of the output Easy adjustability and setting to any levelEasy adjustability and setting to any level An almost constant spectrum at all levelsAn almost constant spectrum at all levels

sphere standards and standard spheres dr. richard young optronic laboratories, inc

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