Richard Young Richard Young Optronic Laboratories Kathleen Muray Kathleen Muray INPHORA Carolyn...
-
Upload
clemence-morgan -
Category
Documents
-
view
217 -
download
0
Transcript of Richard Young Richard Young Optronic Laboratories Kathleen Muray Kathleen Muray INPHORA Carolyn...
CIE 2CIE 2ndnd Expert Symposium on LEDs Expert Symposium on LEDs
Quantifying Quantifying
Photometric Spectral Photometric Spectral
Mismatch Uncertainties Mismatch Uncertainties
in LED Measurementsin LED Measurements
Quantifying Quantifying
Photometric Spectral Photometric Spectral
Mismatch Uncertainties Mismatch Uncertainties
in LED Measurementsin LED Measurements
Richard Young Richard Young Optronic Laboratories
Kathleen Muray Kathleen Muray INPHORA
Carolyn Jones Carolyn Jones CJ Enterprises
Richard Young Richard Young Optronic Laboratories
Kathleen Muray Kathleen Muray INPHORA
Carolyn Jones Carolyn Jones CJ Enterprises
CIE 2CIE 2ndnd Expert Symposium on LEDs Expert Symposium on LEDs
IntroductionIntroductionPhotometer relative responses
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
350 400 450 500 550 600 650 700 750 800
Wavelength [nm]
Rel
ativ
e re
spo
nse
Photopic
Photometer 1
Photometer 2
Photometer 3
Ideally, Ideally, photometer photometer response response
should match should match the photopic the photopic
curvecurve
Ideally, Ideally, photometer photometer response response
should match should match the photopic the photopic
curvecurve
We can see mis-We can see mis-matches at low matches at low response better response better on a logarithmic on a logarithmic
plot.plot.
We can see mis-We can see mis-matches at low matches at low response better response better on a logarithmic on a logarithmic
plot.plot.
CIE 2CIE 2ndnd Expert Symposium on LEDs Expert Symposium on LEDs
IntroductionIntroductionPhotometer relative responses
0.00001
0.0001
0.001
0.01
0.1
1
350 400 450 500 550 600 650 700 750 800
Wavelength [nm]
Re
lati
ve
re
sp
on
se
Photopic
Photometer 1
Photometer 2
Photometer 3
They often They often deviate in the deviate in the
BlueBlue
They often They often deviate in the deviate in the
BlueBlue
Photometers use Photometers use filter/detector filter/detector
combinations to combinations to approximate photopic approximate photopic
responseresponse
Photometers use Photometers use filter/detector filter/detector
combinations to combinations to approximate photopic approximate photopic
responseresponse
This approximation can This approximation can sometimes be quite good, sometimes be quite good,
but is never perfect.but is never perfect.
This approximation can This approximation can sometimes be quite good, sometimes be quite good,
but is never perfect.but is never perfect.
And in And in the Redthe RedAnd in And in
the Redthe Red
The highest The highest response and response and
best fit are best fit are normally normally
around 555 nmaround 555 nm
The highest The highest response and response and
best fit are best fit are normally normally
around 555 nmaround 555 nmThis plot shows 3 This plot shows 3 photometers.photometers.
This plot shows 3 This plot shows 3 photometers.photometers.
Photometer 1Photometer 1Photometer 1Photometer 1Photometer 2Photometer 2Photometer 2Photometer 2Photometer 3Photometer 3Photometer 3Photometer 3
CIE 2CIE 2ndnd Expert Symposium on LEDs Expert Symposium on LEDs
IntroductionIntroduction
If the photometer is calibrated with a white If the photometer is calibrated with a white light source, such as illuminant A:light source, such as illuminant A: Correct measurements will only be made if Correct measurements will only be made if
the test source is also illuminant A.the test source is also illuminant A.The errors in measuring other sources The errors in measuring other sources
depend on:depend on: The accuracy of matching the photometer The accuracy of matching the photometer
response to the photopic curve.response to the photopic curve. The difference between the test source and The difference between the test source and
illuminant A.illuminant A.
If the photometer is calibrated with a white If the photometer is calibrated with a white light source, such as illuminant A:light source, such as illuminant A: Correct measurements will only be made if Correct measurements will only be made if
the test source is also illuminant A.the test source is also illuminant A.The errors in measuring other sources The errors in measuring other sources
depend on:depend on: The accuracy of matching the photometer The accuracy of matching the photometer
response to the photopic curve.response to the photopic curve. The difference between the test source and The difference between the test source and
illuminant A.illuminant A.
CIE 2CIE 2ndnd Expert Symposium on LEDs Expert Symposium on LEDs
IntroductionIntroduction
If the photometer response is very close to If the photometer response is very close to photopic:photopic: There is little error, relaxing the need for There is little error, relaxing the need for
similarity between calibration and test similarity between calibration and test sources.sources.
If the test source is very close to illuminant If the test source is very close to illuminant A:A: There will be little error, relaxing the There will be little error, relaxing the
accuracy requirements of the photometer accuracy requirements of the photometer response.response.
If the photometer response is very close to If the photometer response is very close to photopic:photopic: There is little error, relaxing the need for There is little error, relaxing the need for
similarity between calibration and test similarity between calibration and test sources.sources.
If the test source is very close to illuminant If the test source is very close to illuminant A:A: There will be little error, relaxing the There will be little error, relaxing the
accuracy requirements of the photometer accuracy requirements of the photometer response.response.
CIE 2CIE 2ndnd Expert Symposium on LEDs Expert Symposium on LEDs
IntroductionIntroduction
However, an LED is so different from However, an LED is so different from illuminant A that the photometer needs to illuminant A that the photometer needs to match the photopic response curve match the photopic response curve veryvery closely.closely.
A “goodness of fit” parameter, fA “goodness of fit” parameter, f11’, has ’, has been used for many years as the selection been used for many years as the selection parameter for photometers.parameter for photometers. It is intended to apply to white light sources It is intended to apply to white light sources
and DOES NOT WORK for LEDs (with the and DOES NOT WORK for LEDs (with the possible exception of white LEDs).possible exception of white LEDs).
However, an LED is so different from However, an LED is so different from illuminant A that the photometer needs to illuminant A that the photometer needs to match the photopic response curve match the photopic response curve veryvery closely.closely.
A “goodness of fit” parameter, fA “goodness of fit” parameter, f11’, has ’, has been used for many years as the selection been used for many years as the selection parameter for photometers.parameter for photometers. It is intended to apply to white light sources It is intended to apply to white light sources
and DOES NOT WORK for LEDs (with the and DOES NOT WORK for LEDs (with the possible exception of white LEDs).possible exception of white LEDs).
CIE 2CIE 2ndnd Expert Symposium on LEDs Expert Symposium on LEDs
IntroductionIntroduction
To remind you how fTo remind you how f11’ is defined:’ is defined:To remind you how fTo remind you how f11’ is defined:’ is defined:
0
0
*
'
dV
dVs
= frel
1
Where:Where:Where:Where:
)s(
d )s( S
d )V( S = rel
0relA,
0
A,
rel
)(s*
Illuminant AIlluminant AIlluminant AIlluminant A
Publication CIE 69-1987: Methods of Publication CIE 69-1987: Methods of characterizing illuminance meters and characterizing illuminance meters and
luminance meters: Performance, luminance meters: Performance, characteristics and specificationscharacteristics and specifications
Publication CIE 69-1987: Methods of Publication CIE 69-1987: Methods of characterizing illuminance meters and characterizing illuminance meters and
luminance meters: Performance, luminance meters: Performance, characteristics and specificationscharacteristics and specifications
The calculation requires The calculation requires the photometer relative the photometer relative
response.response.
The calculation requires The calculation requires the photometer relative the photometer relative
response.response.
CIE 2CIE 2ndnd Expert Symposium on LEDs Expert Symposium on LEDs
IntroductionIntroductionPhotometer relative responses
0.00001
0.0001
0.001
0.01
0.1
1
350 400 450 500 550 600 650 700 750 800
Wavelength [nm]
Re
lati
ve
re
sp
on
se
Photopic
Photometer 1
Photometer 2
Photometer 3
LEDs are generally LEDs are generally narrow band, and are very narrow band, and are very
unlike illuminant Aunlike illuminant A
LEDs are generally LEDs are generally narrow band, and are very narrow band, and are very
unlike illuminant Aunlike illuminant A
Measurements of LEDs Measurements of LEDs can therefore have large can therefore have large errors associated with errors associated with white light calibrations.white light calibrations.
Measurements of LEDs Measurements of LEDs can therefore have large can therefore have large errors associated with errors associated with white light calibrations.white light calibrations.
Especially in Especially in the Bluethe Blue
Especially in Especially in the Bluethe Blue
And in And in the Redthe RedAnd in And in
the Redthe Red
CIE 2CIE 2ndnd Expert Symposium on LEDs Expert Symposium on LEDs
IntroductionIntroduction
If the relative spectral distribution of the If the relative spectral distribution of the LED LED andand photometer response are known, photometer response are known, the measured photopic value can be the measured photopic value can be corrected for the difference between the corrected for the difference between the calibration source and the LED.calibration source and the LED. This is called the spectral mismatch This is called the spectral mismatch
correction factor, F (also known as color correction factor, F (also known as color correction factor in some older documents).correction factor in some older documents).
When the calibration source is illuminant A, When the calibration source is illuminant A, the spectral mismatch factor is given the the spectral mismatch factor is given the symbol F*.symbol F*.
If the relative spectral distribution of the If the relative spectral distribution of the LED LED andand photometer response are known, photometer response are known, the measured photopic value can be the measured photopic value can be corrected for the difference between the corrected for the difference between the calibration source and the LED.calibration source and the LED. This is called the spectral mismatch This is called the spectral mismatch
correction factor, F (also known as color correction factor, F (also known as color correction factor in some older documents).correction factor in some older documents).
When the calibration source is illuminant A, When the calibration source is illuminant A, the spectral mismatch factor is given the the spectral mismatch factor is given the symbol F*.symbol F*.
CIE 2CIE 2ndnd Expert Symposium on LEDs Expert Symposium on LEDs
Spectral Mismatch FactorsSpectral Mismatch FactorsLED relative spectral distributions
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
350 400 450 500 550 600 650 700 750 800
Wavelength [nm]
Re
lati
ve
In
ten
sit
y
Here are the spectral Here are the spectral distributions for a range of distributions for a range of
LEDsLEDs
Here are the spectral Here are the spectral distributions for a range of distributions for a range of
LEDsLEDs
We can therefore calculate the We can therefore calculate the spectral mismatch factors for spectral mismatch factors for
Photometer 1.Photometer 1.
We can therefore calculate the We can therefore calculate the spectral mismatch factors for spectral mismatch factors for
Photometer 1.Photometer 1.
CIE 2CIE 2ndnd Expert Symposium on LEDs Expert Symposium on LEDs
Spectral Mismatch FactorsSpectral Mismatch FactorsF* for a photometer measuring LEDs
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
2.2
400 450 500 550 600 650 700
LED Peak Wavelength [nm]
F*
Photometer 1
IDEAL
Actual LEDs
LED measurements using this LED measurements using this photometer, can be multiplied photometer, can be multiplied by the appropriate F* to give by the appropriate F* to give
corrected results.corrected results.
LED measurements using this LED measurements using this photometer, can be multiplied photometer, can be multiplied by the appropriate F* to give by the appropriate F* to give
corrected results.corrected results.
CIE 2CIE 2ndnd Expert Symposium on LEDs Expert Symposium on LEDs
Spectral Mismatch FactorsSpectral Mismatch Factors
Can we calculate the spectral mismatch Can we calculate the spectral mismatch factors without measuring a whole range factors without measuring a whole range of LEDs?of LEDs? Although spectral distributions of LEDs are Although spectral distributions of LEDs are
often asymmetric, they have a similarity of often asymmetric, they have a similarity of shape that might be reproduced by shape that might be reproduced by calculation.calculation.
To keep the calculation simple and To keep the calculation simple and relevant, it should be based on information relevant, it should be based on information readily available: peak wavelength and full-readily available: peak wavelength and full-width-at-half-maximum (FWHM).width-at-half-maximum (FWHM).
Can we calculate the spectral mismatch Can we calculate the spectral mismatch factors without measuring a whole range factors without measuring a whole range of LEDs?of LEDs? Although spectral distributions of LEDs are Although spectral distributions of LEDs are
often asymmetric, they have a similarity of often asymmetric, they have a similarity of shape that might be reproduced by shape that might be reproduced by calculation.calculation.
To keep the calculation simple and To keep the calculation simple and relevant, it should be based on information relevant, it should be based on information readily available: peak wavelength and full-readily available: peak wavelength and full-width-at-half-maximum (FWHM).width-at-half-maximum (FWHM).
CIE 2CIE 2ndnd Expert Symposium on LEDs Expert Symposium on LEDs
Spectral Mismatch FactorsSpectral Mismatch Factors
Using a Gaussian curve within the FWHM Using a Gaussian curve within the FWHM limits and an exponential curve outside, limits and an exponential curve outside, the LED spectrum is represented the LED spectrum is represented reasonably well.reasonably well.
Using a Gaussian curve within the FWHM Using a Gaussian curve within the FWHM limits and an exponential curve outside, limits and an exponential curve outside, the LED spectrum is represented the LED spectrum is represented reasonably well.reasonably well.
CIE 2CIE 2ndnd Expert Symposium on LEDs Expert Symposium on LEDs
Spectral Mismatch FactorsSpectral Mismatch Factors
Mathematically, for Mathematically, for LL H H
[[LL is the lower and is the lower and HH is the upper FWHM is the upper FWHM limit, limit, pp is the peak wavelength] is the peak wavelength]
Mathematically, for Mathematically, for LL H H
[[LL is the lower and is the lower and HH is the upper FWHM is the upper FWHM limit, limit, pp is the peak wavelength] is the peak wavelength]
2
25.0ln4
FWHM
p
e
CIE 2CIE 2ndnd Expert Symposium on LEDs Expert Symposium on LEDs
Spectral Mismatch FactorsSpectral Mismatch Factors
For For L L and and H H > >
[[LL is the lower and is the lower and HH is the upper FWHM is the upper FWHM
limit, limit, pp is the peak wavelength] is the peak wavelength]
For For L L and and H H > >
[[LL is the lower and is the lower and HH is the upper FWHM is the upper FWHM
limit, limit, pp is the peak wavelength] is the peak wavelength]
FWHM
p
e
5.0ln4
2
CIE 2CIE 2ndnd Expert Symposium on LEDs Expert Symposium on LEDs
F* for a photometer measuring LEDs
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
2.2
400 450 500 550 600 650 700
LED Peak Wavelength [nm]
F*
Photometer 1
IDEAL
Actual LEDs
So, here are the F* factors So, here are the F* factors calculated from real LED calculated from real LED
spectra again…spectra again…
So, here are the F* factors So, here are the F* factors calculated from real LED calculated from real LED
spectra again…spectra again…
F* for a photometer measuring LEDs
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
2.2
400 450 500 550 600 650 700
LED Peak Wavelength [nm]
F*
Photometer 1
IDEAL
Actual LEDs
Calculated LEDs
……and here are the predicted and here are the predicted F* values using the modelled F* values using the modelled LED spectra (shown in red).LED spectra (shown in red).
……and here are the predicted and here are the predicted F* values using the modelled F* values using the modelled LED spectra (shown in red).LED spectra (shown in red).
Spectral Mismatch FactorsSpectral Mismatch Factors
CIE 2CIE 2ndnd Expert Symposium on LEDs Expert Symposium on LEDs
Spectral Mismatch FactorsSpectral Mismatch Factors
The agreement between real and modelled The agreement between real and modelled LED spectral calculations means we can LED spectral calculations means we can express F* as a smooth curve rather than express F* as a smooth curve rather than individual points.individual points.
We don’t have to do all those LED spectral We don’t have to do all those LED spectral measurements.measurements.
We can express F* for different FWHM We can express F* for different FWHM values at each peak wavelength.values at each peak wavelength. And then something interesting happens…And then something interesting happens…
The agreement between real and modelled The agreement between real and modelled LED spectral calculations means we can LED spectral calculations means we can express F* as a smooth curve rather than express F* as a smooth curve rather than individual points.individual points.
We don’t have to do all those LED spectral We don’t have to do all those LED spectral measurements.measurements.
We can express F* for different FWHM We can express F* for different FWHM values at each peak wavelength.values at each peak wavelength. And then something interesting happens…And then something interesting happens…
CIE 2CIE 2ndnd Expert Symposium on LEDs Expert Symposium on LEDs
Spectral Mismatch FactorsSpectral Mismatch FactorsF* for a photometer measuring LEDs
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
2.2
400 450 500 550 600 650 700
LED Peak Wavelength [nm]
F*
Photometer 1IDEAL
20 nm FWHM
30 nm FWHM
40 nm FWHM
50 nm FWHM
70 nm FWHM
Actual LEDs
Calculated LEDs
We see that the F* curve We see that the F* curve has places where FWHM has places where FWHM
hardly mattershardly matters
We see that the F* curve We see that the F* curve has places where FWHM has places where FWHM
hardly mattershardly matters
And other places where And other places where F* changes rapidly with F* changes rapidly with
FWHMFWHM
And other places where And other places where F* changes rapidly with F* changes rapidly with
FWHMFWHM
There are wavelength There are wavelength ranges where F* ranges where F* changes rapidlychanges rapidly
There are wavelength There are wavelength ranges where F* ranges where F* changes rapidlychanges rapidly
And other ranges where And other ranges where F* hardly changes at allF* hardly changes at allAnd other ranges where And other ranges where F* hardly changes at allF* hardly changes at all
CIE 2CIE 2ndnd Expert Symposium on LEDs Expert Symposium on LEDs
Spectral Mismatch FactorsSpectral Mismatch Factors
LEDs differ in peak wavelength and LEDs differ in peak wavelength and FWHM, so if we want to describe how F* FWHM, so if we want to describe how F* changes for real LEDs:changes for real LEDs: We must include a wavelength componentWe must include a wavelength component We must include a FWHM componentWe must include a FWHM component
LEDs differ in peak wavelength and LEDs differ in peak wavelength and FWHM, so if we want to describe how F* FWHM, so if we want to describe how F* changes for real LEDs:changes for real LEDs: We must include a wavelength componentWe must include a wavelength component We must include a FWHM componentWe must include a FWHM component
CIE 2CIE 2ndnd Expert Symposium on LEDs Expert Symposium on LEDs
Spectral Mismatch FactorsSpectral Mismatch Factors
The mathematical model for the LED The mathematical model for the LED spectra works for this photometer, but spectra works for this photometer, but does it work for all?does it work for all?
The mathematical model for the LED The mathematical model for the LED spectra works for this photometer, but spectra works for this photometer, but does it work for all?does it work for all?
CIE 2CIE 2ndnd Expert Symposium on LEDs Expert Symposium on LEDs
Spectral Mismatch FactorsSpectral Mismatch FactorsF* for a photometer measuring LEDs
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
2.2
400 450 500 550 600 650 700
LED Peak Wavelength [nm]
F*
Photometer 2IDEAL
20 nm FWHM
30 nm FWHM
40 nm FWHM
50 nm FWHM
70 nm FWHM
Actual LEDs
Calculated LEDs
It seems to work even better It seems to work even better for Photometer 2 than it did for Photometer 2 than it did
for Photometer 1.for Photometer 1.
It seems to work even better It seems to work even better for Photometer 2 than it did for Photometer 2 than it did
for Photometer 1.for Photometer 1.
CIE 2CIE 2ndnd Expert Symposium on LEDs Expert Symposium on LEDs
F* for a photometer measuring LEDs
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
2.2
400 450 500 550 600 650 700
LED Peak Wavelength [nm]
F*
Photometer 3IDEAL
20 nm FWHM
30 nm FWHM
40 nm FWHM
50 nm FWHM
70 nm FWHM
Actual LEDs
Calculated LEDs
Spectral Mismatch FactorsSpectral Mismatch Factors
Photometer 3 Photometer 3 shows some shows some
differences as the differences as the F* value increasesF* value increases
Photometer 3 Photometer 3 shows some shows some
differences as the differences as the F* value increasesF* value increases
This is because the mathematical This is because the mathematical model is symmetric and the LED model is symmetric and the LED spectrum is not. These LEDs are spectrum is not. These LEDs are
narrow band and highly narrow band and highly asymmetric, combined with a asymmetric, combined with a
poor photopic fit of the detectorpoor photopic fit of the detector
This is because the mathematical This is because the mathematical model is symmetric and the LED model is symmetric and the LED spectrum is not. These LEDs are spectrum is not. These LEDs are
narrow band and highly narrow band and highly asymmetric, combined with a asymmetric, combined with a
poor photopic fit of the detectorpoor photopic fit of the detector
However, it still matches the However, it still matches the general shape of the F* curve, general shape of the F* curve,
which is all that is required in this which is all that is required in this paper.paper.
However, it still matches the However, it still matches the general shape of the F* curve, general shape of the F* curve,
which is all that is required in this which is all that is required in this paper.paper.
CIE 2CIE 2ndnd Expert Symposium on LEDs Expert Symposium on LEDs
Spectral Mismatch FactorsSpectral Mismatch Factors
The point of this presentation is not to replace The point of this presentation is not to replace LED spectral measurement in the calculation of LED spectral measurement in the calculation of spectral mismatch factors.spectral mismatch factors. Though it seems to do a good job of this.Though it seems to do a good job of this.
The point is, when testing LEDs in a production The point is, when testing LEDs in a production environment, there are small changes in peak environment, there are small changes in peak wavelength and FWHM between devices of the wavelength and FWHM between devices of the same type.same type. And measuring the spectrum, or even peak And measuring the spectrum, or even peak
wavelength, to get a new F* for each device is not wavelength, to get a new F* for each device is not practical.practical.
The point of this presentation is not to replace The point of this presentation is not to replace LED spectral measurement in the calculation of LED spectral measurement in the calculation of spectral mismatch factors.spectral mismatch factors. Though it seems to do a good job of this.Though it seems to do a good job of this.
The point is, when testing LEDs in a production The point is, when testing LEDs in a production environment, there are small changes in peak environment, there are small changes in peak wavelength and FWHM between devices of the wavelength and FWHM between devices of the same type.same type. And measuring the spectrum, or even peak And measuring the spectrum, or even peak
wavelength, to get a new F* for each device is not wavelength, to get a new F* for each device is not practical.practical.
CIE 2CIE 2ndnd Expert Symposium on LEDs Expert Symposium on LEDs
Spectral Mismatch FactorsSpectral Mismatch Factors
At this point it is worth noting that if a calibrated At this point it is worth noting that if a calibrated LED is used to calibrate the photometer rather LED is used to calibrate the photometer rather than a white light source, the photometer will than a white light source, the photometer will already read correctly for that LED.already read correctly for that LED. It is equivalent to calibrating It is equivalent to calibrating andand applying the F* applying the F*
factor in one process.factor in one process.
All other LEDs will still need a spectral mismatch All other LEDs will still need a spectral mismatch factor, F, to correct the measurement result.factor, F, to correct the measurement result. And that includes the production devices.And that includes the production devices.
At this point it is worth noting that if a calibrated At this point it is worth noting that if a calibrated LED is used to calibrate the photometer rather LED is used to calibrate the photometer rather than a white light source, the photometer will than a white light source, the photometer will already read correctly for that LED.already read correctly for that LED. It is equivalent to calibrating It is equivalent to calibrating andand applying the F* applying the F*
factor in one process.factor in one process.
All other LEDs will still need a spectral mismatch All other LEDs will still need a spectral mismatch factor, F, to correct the measurement result.factor, F, to correct the measurement result. And that includes the production devices.And that includes the production devices.
CIE 2CIE 2ndnd Expert Symposium on LEDs Expert Symposium on LEDs
Spectral Mismatch FactorsSpectral Mismatch FactorsF* for a photometer measuring LEDs
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
2.2
400 450 500 550 600 650 700
LED Peak Wavelength [nm]
F*
Photometer 3
IDEAL
20 nm FWHM
30 nm FWHM
40 nm FWHM
50 nm FWHM
70 nm FWHM
Let us take a closer Let us take a closer look at some of these look at some of these
F* values.F* values.
Let us take a closer Let us take a closer look at some of these look at some of these
F* values.F* values.
MagnifyMagnifyMagnifyMagnify
CIE 2CIE 2ndnd Expert Symposium on LEDs Expert Symposium on LEDs
F* for a photometer measuring LEDs
1.0
1.2
1.4
1.6
1.8
2.0
2.2
430 435 440 445 450 455 460 465 470 475 480
LED Peak Wavelength [nm]
F*
Photometer 3
IDEAL
20 nm FWHM
30 nm FWHM
40 nm FWHM
50 nm FWHM
70 nm FWHM
Spectral Mismatch FactorsSpectral Mismatch Factors
When we apply the F* When we apply the F* factor, we are effectively factor, we are effectively
offsetting the curve at offsetting the curve at one wavelengthone wavelength
When we apply the F* When we apply the F* factor, we are effectively factor, we are effectively
offsetting the curve at offsetting the curve at one wavelengthone wavelength
This means that This means that measurements of LEDs measurements of LEDs
that have a slightly that have a slightly different wavelength still different wavelength still have an associated errorhave an associated error
This means that This means that measurements of LEDs measurements of LEDs
that have a slightly that have a slightly different wavelength still different wavelength still have an associated errorhave an associated error
The size of the error The size of the error depends on how different depends on how different
the wavelength is and the wavelength is and how quickly the F* factor how quickly the F* factor changes in that region.changes in that region.
The size of the error The size of the error depends on how different depends on how different
the wavelength is and the wavelength is and how quickly the F* factor how quickly the F* factor changes in that region.changes in that region.
CIE 2CIE 2ndnd Expert Symposium on LEDs Expert Symposium on LEDs
ffLEDLED
We can define a “goodness of fit” We can define a “goodness of fit” parameter, like fparameter, like f11’ but specifically applying ’ but specifically applying
to LEDs – fto LEDs – fLEDLED..
The fThe fLED LED parameter is “the average absolute parameter is “the average absolute
spectral mismatch error over a wavelength spectral mismatch error over a wavelength region relative to the central wavelength of region relative to the central wavelength of that region.”that region.”
We can define a “goodness of fit” We can define a “goodness of fit” parameter, like fparameter, like f11’ but specifically applying ’ but specifically applying
to LEDs – fto LEDs – fLEDLED..
The fThe fLED LED parameter is “the average absolute parameter is “the average absolute
spectral mismatch error over a wavelength spectral mismatch error over a wavelength region relative to the central wavelength of region relative to the central wavelength of that region.”that region.”
NOTE: It is NOTE: It is NOTNOT a correction factor to a correction factor to be applied, but it be applied, but it ISIS an indicator of the an indicator of the
suitability and quality of the suitability and quality of the photometer for measurement of any photometer for measurement of any
single color LED.single color LED.
NOTE: It is NOTE: It is NOTNOT a correction factor to a correction factor to be applied, but it be applied, but it ISIS an indicator of the an indicator of the
suitability and quality of the suitability and quality of the photometer for measurement of any photometer for measurement of any
single color LED.single color LED.
CIE 2CIE 2ndnd Expert Symposium on LEDs Expert Symposium on LEDs
ffLEDLED
There is one value of fThere is one value of fLEDLED for each for each wavelength and FWHM, but because we can wavelength and FWHM, but because we can effectively model the LED spectral effectively model the LED spectral distribution, it can be easily calculated from distribution, it can be easily calculated from the photometer response.the photometer response.
ffLEDLED has two components. has two components. Errors introduced by measuring LEDs at Errors introduced by measuring LEDs at
different wavelengths to the calibration –wdifferent wavelengths to the calibration –wLEDLED.. Errors introduced by measuring LEDs at Errors introduced by measuring LEDs at
different FWHMs to the calibration – hdifferent FWHMs to the calibration – hLEDLED..
There is one value of fThere is one value of fLEDLED for each for each wavelength and FWHM, but because we can wavelength and FWHM, but because we can effectively model the LED spectral effectively model the LED spectral distribution, it can be easily calculated from distribution, it can be easily calculated from the photometer response.the photometer response.
ffLEDLED has two components. has two components. Errors introduced by measuring LEDs at Errors introduced by measuring LEDs at
different wavelengths to the calibration –wdifferent wavelengths to the calibration –wLEDLED.. Errors introduced by measuring LEDs at Errors introduced by measuring LEDs at
different FWHMs to the calibration – hdifferent FWHMs to the calibration – hLEDLED..
CIE 2CIE 2ndnd Expert Symposium on LEDs Expert Symposium on LEDs
wwLEDLED
Mathematically, the F* value for an LED at Mathematically, the F* value for an LED at the central wavelength, c, is:the central wavelength, c, is: Where Where s(s()) is the photometer response and is the photometer response and SScc
LEDLED(() is the LED spectral distribution.) is the LED spectral distribution.
Mathematically, the F* value for an LED at Mathematically, the F* value for an LED at the central wavelength, c, is:the central wavelength, c, is: Where Where s(s()) is the photometer response and is the photometer response and SScc
LEDLED(() is the LED spectral distribution.) is the LED spectral distribution.
dsSdVS
dVSdsSF
LEDcA
LEDcA
c..
..*
CIE 2CIE 2ndnd Expert Symposium on LEDs Expert Symposium on LEDs
wwLEDLED
Similarly, the F* value for an LED at some Similarly, the F* value for an LED at some other wavelength, p, is:other wavelength, p, is: Where Where s(s()) is the photometer response and is the photometer response and SSpp
LEDLED(() is the LED spectral distribution.) is the LED spectral distribution.
Similarly, the F* value for an LED at some Similarly, the F* value for an LED at some other wavelength, p, is:other wavelength, p, is: Where Where s(s()) is the photometer response and is the photometer response and SSpp
LEDLED(() is the LED spectral distribution.) is the LED spectral distribution.
dsSdVS
dVSdsSF
LEDpA
LEDpA
p..
..*
CIE 2CIE 2ndnd Expert Symposium on LEDs Expert Symposium on LEDs
The error when measuring an LED at The error when measuring an LED at wavelength p using the Fwavelength p using the Fcc* value at * value at
wavelength c is:wavelength c is:
The error when measuring an LED at The error when measuring an LED at wavelength p using the Fwavelength p using the Fcc* value at * value at
wavelength c is:wavelength c is:
NOTE: This equation no longer contains a reference to NOTE: This equation no longer contains a reference to the calibration source, so it does not matter if it was the calibration source, so it does not matter if it was
calibrated with white light or a calibrated LED.calibrated with white light or a calibrated LED.
p,cp,c depends only on the photometer and the LED depends only on the photometer and the LED
spectral distributions. If the modelled spectral spectral distributions. If the modelled spectral distributions are used, it is purely a photometer distributions are used, it is purely a photometer
characteristic.characteristic.
NOTE: This equation no longer contains a reference to NOTE: This equation no longer contains a reference to the calibration source, so it does not matter if it was the calibration source, so it does not matter if it was
calibrated with white light or a calibrated LED.calibrated with white light or a calibrated LED.
p,cp,c depends only on the photometer and the LED depends only on the photometer and the LED
spectral distributions. If the modelled spectral spectral distributions. If the modelled spectral distributions are used, it is purely a photometer distributions are used, it is purely a photometer
characteristic.characteristic.
dsSdVS
dVSdsSLEDp
LEDc
LEDp
LEDc
cp..
..1,
wwLEDLED
*
*1,
c
pcp F
F
CIE 2CIE 2ndnd Expert Symposium on LEDs Expert Symposium on LEDs
wwLEDLED
Recall the definition of fRecall the definition of fLEDLED:: ““the average absolute spectral mismatch the average absolute spectral mismatch
error over a wavelength region relative to error over a wavelength region relative to the central wavelength of that region.”the central wavelength of that region.”
We can now define wWe can now define wLEDLED in mathematical in mathematical
terms:terms:
Recall the definition of fRecall the definition of fLEDLED:: ““the average absolute spectral mismatch the average absolute spectral mismatch
error over a wavelength region relative to error over a wavelength region relative to the central wavelength of that region.”the central wavelength of that region.”
We can now define wWe can now define wLEDLED in mathematical in mathematical
terms:terms:
12
.
)(
2
1
,
pp
dp
cw
p
p
cp
LED
Where p1 and p2 Where p1 and p2 are the are the
wavelength wavelength limits of the limits of the
regionregion
Where p1 and p2 Where p1 and p2 are the are the
wavelength wavelength limits of the limits of the
regionregion
CIE 2CIE 2ndnd Expert Symposium on LEDs Expert Symposium on LEDs
wwLEDLED
So wSo wLEDLED can be calculated for any central can be calculated for any central
wavelength and FWHM.wavelength and FWHM. It should be shown as wIt should be shown as wLEDLED(c,FWHM) to reflect (c,FWHM) to reflect
this.this. Since it is independent of calibration source, a Since it is independent of calibration source, a
full photometer response curve is not required.full photometer response curve is not required. 3 FWHMs around the central wavelength should 3 FWHMs around the central wavelength should
be sufficient.be sufficient.
The photometer response The photometer response doesdoes need to be done need to be done at 1nm intervals or smaller for good results.at 1nm intervals or smaller for good results.
So wSo wLEDLED can be calculated for any central can be calculated for any central
wavelength and FWHM.wavelength and FWHM. It should be shown as wIt should be shown as wLEDLED(c,FWHM) to reflect (c,FWHM) to reflect
this.this. Since it is independent of calibration source, a Since it is independent of calibration source, a
full photometer response curve is not required.full photometer response curve is not required. 3 FWHMs around the central wavelength should 3 FWHMs around the central wavelength should
be sufficient.be sufficient.
The photometer response The photometer response doesdoes need to be done need to be done at 1nm intervals or smaller for good results.at 1nm intervals or smaller for good results.
CIE 2CIE 2ndnd Expert Symposium on LEDs Expert Symposium on LEDs
wwLEDLED
We still need to define the wavelength We still need to define the wavelength “region” in order to calculate “region” in order to calculate wwLEDLED(c,FWHM).(c,FWHM).
Based on data for over 900 LEDs in 63 Based on data for over 900 LEDs in 63 batches, covering most of the visible batches, covering most of the visible range, we propose range, we propose ± 5 nm around the ± 5 nm around the central wavelength.central wavelength.
We still need to define the wavelength We still need to define the wavelength “region” in order to calculate “region” in order to calculate wwLEDLED(c,FWHM).(c,FWHM).
Based on data for over 900 LEDs in 63 Based on data for over 900 LEDs in 63 batches, covering most of the visible batches, covering most of the visible range, we propose range, we propose ± 5 nm around the ± 5 nm around the central wavelength.central wavelength.
CIE 2CIE 2ndnd Expert Symposium on LEDs Expert Symposium on LEDs
wwLEDLED4
30
44
0
45
0
46
0
47
0
48
0
49
0
50
0
51
0
52
0
53
0
54
0
55
0
56
0
57
0
58
0
59
0
60
0
61
0
62
0
63
0
64
0
65
0
66
0-5 -4 -3 -2 -1 0 1 2 3 4 5
-11%-10%-9%-8%-7%-6%-5%-4%-3%-2%-1%0%1%2%3%4%5%6%7%8%9%10%
p,c
CentralWavelength [nm]
c-p
-11%--10% -10%--9% -9%--8% -8%--7%-7%--6% -6%--5% -5%--4% -4%--3%-3%--2% -2%--1% -1%-0% 0%-1%1%-2% 2%-3% 3%-4% 4%-5%5%-6% 6%-7% 7%-8% 8%-9%9%-10%
The first stage is to calculate The first stage is to calculate p,cp,c
over the region.over the region.The first stage is to calculate The first stage is to calculate p,cp,c
over the region.over the region.
This is the result This is the result for photometer 1 for photometer 1 at 20 nm FWHM.at 20 nm FWHM.
This is the result This is the result for photometer 1 for photometer 1 at 20 nm FWHM.at 20 nm FWHM.
CIE 2CIE 2ndnd Expert Symposium on LEDs Expert Symposium on LEDs
wLED values for photometer 1 vs central wavelength & FWHM
0%
1%
2%
3%
4%
5%
6%
7%
400 450 500 550 600 650
Central Wavelength [nm]
wLE
D
10 nm
15 nm
20 nm
25 nm
30 nm
35 nm
40 nm
45 nm
50 nm
55 nm
60 nm
65 nm
70 nm
wwLEDLED
The next stage is to The next stage is to calculate wcalculate wLEDLED values. values.The next stage is to The next stage is to
calculate wcalculate wLEDLED values. values.
These results These results show that wshow that wLEDLED
varies strongly varies strongly with FWHM.with FWHM.
These results These results show that wshow that wLEDLED
varies strongly varies strongly with FWHM.with FWHM.
CIE 2CIE 2ndnd Expert Symposium on LEDs Expert Symposium on LEDs
Using similar reasoning to wUsing similar reasoning to wLEDLED
calculationscalculations The error when measuring an LED at FWHM The error when measuring an LED at FWHM
h using the Fh using the FHH* value at FWHM H, both at * value at FWHM H, both at peak wavelength c is:peak wavelength c is:
Using similar reasoning to wUsing similar reasoning to wLEDLED
calculationscalculations The error when measuring an LED at FWHM The error when measuring an LED at FWHM
h using the Fh using the FHH* value at FWHM H, both at * value at FWHM H, both at peak wavelength c is:peak wavelength c is:
dsSdVS
dVSdsSLED
hcLED
Hc
LEDhc
LEDHc
Hh..
..1
,,
,,
,
hhLEDLED
*
*1
,
,,
Hc
hcHh F
F
CIE 2CIE 2ndnd Expert Symposium on LEDs Expert Symposium on LEDs
hhLEDLED
We can define hWe can define hLEDLED in similar mathematical in similar mathematical
terms to wterms to wLEDLED::
We can define hWe can define hLEDLED in similar mathematical in similar mathematical
terms to wterms to wLEDLED::
12
.
),(
2
1
,
hh
dh
Hch
h
h
Hh
LED
Where h1 and h2 Where h1 and h2 are are ± 5 nm limits ± 5 nm limits
around the around the central FWHM central FWHM
value, Hvalue, H
Where h1 and h2 Where h1 and h2 are are ± 5 nm limits ± 5 nm limits
around the around the central FWHM central FWHM
value, Hvalue, H
CIE 2CIE 2ndnd Expert Symposium on LEDs Expert Symposium on LEDs
hhLEDLEDhLED values for photometer 1 vs central wavelength & FWHM
0%
1%
2%
3%
4%
5%
6%
400 450 500 550 600 650
Region central wavelength [nm]
fLE
D
10 nm
15 nm
20 nm
25 nm
30 nm
35 nm
40 nm
45 nm
50 nm
55 nm
60 nm
65 nm
70 nm
Like wLike wLEDLED, h, hLEDLED is is
strongly dependent strongly dependent on FWHM.on FWHM.
Like wLike wLEDLED, h, hLEDLED is is
strongly dependent strongly dependent on FWHM.on FWHM.
CIE 2CIE 2ndnd Expert Symposium on LEDs Expert Symposium on LEDs
hhLEDLED
So now we have the two components:So now we have the two components: wwLEDLED(c,H) gives the error for peak (c,H) gives the error for peak
wavelength change.wavelength change. hhLED LED (c,H) gives the error for FWHM change.(c,H) gives the error for FWHM change.
We can combine them to give the general We can combine them to give the general error indicator, ferror indicator, fLEDLED(c,H):(c,H):
So now we have the two components:So now we have the two components: wwLEDLED(c,H) gives the error for peak (c,H) gives the error for peak
wavelength change.wavelength change. hhLED LED (c,H) gives the error for FWHM change.(c,H) gives the error for FWHM change.
We can combine them to give the general We can combine them to give the general error indicator, ferror indicator, fLEDLED(c,H):(c,H):
5.022 ,,, HchHcwHcf LEDLEDLED
CIE 2CIE 2ndnd Expert Symposium on LEDs Expert Symposium on LEDs
ffLEDLEDComponents of fLED for photometer 1 at 20 nm FWHM
0%
1%
2%
3%
4%
5%
6%
7%
8%
400 450 500 550 600 650
Wavelength [nm]
wLE
D o
r h
LED o
r f L
ED
wLED
Components of fLED for photometer 1 at 20 nm FWHM
0%
1%
2%
3%
4%
5%
6%
7%
8%
400 450 500 550 600 650
Wavelength [nm]
wLE
D o
r h
LED o
r f L
ED
hLED
Components of fLED for photometer 1 at 20 nm FWHM
0%
1%
2%
3%
4%
5%
6%
7%
8%
400 450 500 550 600 650
Wavelength [nm]
wLE
D o
r h
LED o
r f L
ED
fLED
Here is an Here is an example of wexample of wLEDLED
Here is an Here is an example of wexample of wLEDLED
We add hWe add hLEDLEDWe add hWe add hLEDLEDAnd finally fAnd finally fLED.LED.And finally fAnd finally fLED.LED.
You can see that high hYou can see that high hLEDLED is is
generally close to a low wgenerally close to a low wLED.LED.
You can see that high hYou can see that high hLEDLED is is
generally close to a low wgenerally close to a low wLED.LED.This means there are wavelengths This means there are wavelengths
where the photometer error is more where the photometer error is more sensitive to LED peak wavelength sensitive to LED peak wavelength shifts and others where it is more shifts and others where it is more
sensitive to FWHM changes.sensitive to FWHM changes.
This means there are wavelengths This means there are wavelengths where the photometer error is more where the photometer error is more sensitive to LED peak wavelength sensitive to LED peak wavelength shifts and others where it is more shifts and others where it is more
sensitive to FWHM changes.sensitive to FWHM changes.
CIE 2CIE 2ndnd Expert Symposium on LEDs Expert Symposium on LEDs
ffLEDLED
Photometer relative responses
0.001
0.01
0.1
1
380 400 420 440 460 480 500
Wavelength [nm]
Rel
ativ
e re
spo
nse
Photopic
Photometer 1
Photometer 2
Photometer 3
This is the This is the photometer response photometer response graph shown earlier graph shown earlier
but rescaled.but rescaled.
This is the This is the photometer response photometer response graph shown earlier graph shown earlier
but rescaled.but rescaled.
Where the photometer Where the photometer response crosses the response crosses the photopic curve, their photopic curve, their
slopes are very differentslopes are very different
Where the photometer Where the photometer response crosses the response crosses the photopic curve, their photopic curve, their
slopes are very differentslopes are very different
Giving large errors with Giving large errors with wavelength changeswavelength changes
Giving large errors with Giving large errors with wavelength changeswavelength changes
But high and low But high and low contributions offset one contributions offset one another for changes in another for changes in
FWHM.FWHM.
But high and low But high and low contributions offset one contributions offset one another for changes in another for changes in
FWHM.FWHM.
CIE 2CIE 2ndnd Expert Symposium on LEDs Expert Symposium on LEDs
ffLEDLED
ffLEDLED(c,H) values can aid in the design of (c,H) values can aid in the design of photometers.photometers. It provides instant feedback on the performance It provides instant feedback on the performance
of the photometer for LED measurements.of the photometer for LED measurements. It shows that it is the slope of the response It shows that it is the slope of the response
rather than the absolute value that is important.rather than the absolute value that is important. It does not require spectral data over the full It does not require spectral data over the full
visible region.visible region.Photometer 4, specially designed for blue Photometer 4, specially designed for blue
LEDs, can now be added to our list.LEDs, can now be added to our list.
ffLEDLED(c,H) values can aid in the design of (c,H) values can aid in the design of photometers.photometers. It provides instant feedback on the performance It provides instant feedback on the performance
of the photometer for LED measurements.of the photometer for LED measurements. It shows that it is the slope of the response It shows that it is the slope of the response
rather than the absolute value that is important.rather than the absolute value that is important. It does not require spectral data over the full It does not require spectral data over the full
visible region.visible region.Photometer 4, specially designed for blue Photometer 4, specially designed for blue
LEDs, can now be added to our list.LEDs, can now be added to our list.
CIE 2CIE 2ndnd Expert Symposium on LEDs Expert Symposium on LEDs
ffLEDLEDComparison of Photometers at 20 nm FWHM
0%
1%
2%
3%
4%
5%
6%
7%
8%
400 450 500 550 600 650
Wavelength, c [nm]
f LE
D(c
,20)
Photometer 1
Photometer 2
Photometer 3
Photometer 4
Photometer 4 is Photometer 4 is confirmed as confirmed as
generally the best generally the best for blue LEDS.for blue LEDS.
Photometer 4 is Photometer 4 is confirmed as confirmed as
generally the best generally the best for blue LEDS.for blue LEDS.
But photometer 1 But photometer 1 is best at 430 nm.is best at 430 nm.But photometer 1 But photometer 1 is best at 430 nm.is best at 430 nm.
CIE 2CIE 2ndnd Expert Symposium on LEDs Expert Symposium on LEDs
Comparison of Photometers at 40 nm FWHM
0%
1%
2%
3%
4%
400 450 500 550 600 650
Wavelength, c [nm]
f LE
D(c
,40)
Photometer 1
Photometer 2
Photometer 3
Photometer 4
ffLEDLED
At 40 nm FWHM At 40 nm FWHM Photometer 4 is the Photometer 4 is the best for blue LEDS best for blue LEDS
even at 430 nmeven at 430 nm
At 40 nm FWHM At 40 nm FWHM Photometer 4 is the Photometer 4 is the best for blue LEDS best for blue LEDS
even at 430 nmeven at 430 nm
Photometer 3 Photometer 3 is the worstis the worst
Photometer 3 Photometer 3 is the worstis the worstValues of fValues of fLEDLED(c,H) (c,H)
show the suitability show the suitability for LED measurement, for LED measurement, but bear no relation to but bear no relation to
the fthe f11’ value.’ value.
Values of fValues of fLEDLED(c,H) (c,H)
show the suitability show the suitability for LED measurement, for LED measurement, but bear no relation to but bear no relation to
the fthe f11’ value.’ value.
Photometer 2: fPhotometer 2: f11’ = 1.98%’ = 1.98%Photometer 2: fPhotometer 2: f11’ = 1.98%’ = 1.98%
Photometer 1: fPhotometer 1: f11’ = 6.35%’ = 6.35%Photometer 1: fPhotometer 1: f11’ = 6.35%’ = 6.35%
Photometer 3: fPhotometer 3: f11’ = 2.51%’ = 2.51%Photometer 3: fPhotometer 3: f11’ = 2.51%’ = 2.51%
CIE 2CIE 2ndnd Expert Symposium on LEDs Expert Symposium on LEDs
430
460
490
520
550
580
610
64010 nm
20 nm
30 nm
40 nm
50 nm
60 nm
70 nm
0.0%0.5%1.0%1.5%2.0%2.5%3.0%3.5%4.0%4.5%5.0%5.5%6.0%6.5%7.0%7.5%8.0%
f LE
D(c
,H)
Wavelength, c [nm]
FWHM, H [nm]
fLED(c,H) for photometer 1
7.50%-8.00%7.00%-7.50%6.50%-7.00%6.00%-6.50%5.50%-6.00%5.00%-5.50%4.50%-5.00%4.00%-4.50%3.50%-4.00%3.00%-3.50%2.50%-3.00%2.00%-2.50%1.50%-2.00%1.00%-1.50%0.50%-1.00%0.00%-0.50%
ffLEDLED
A 3-D plot A 3-D plot shows the shows the
variations of variations of ffLEDLED(c,H). The (c,H). The
value is color value is color coded to show coded to show
iso-value iso-value lines. Seen lines. Seen from above, from above,
this is a map.this is a map.
A 3-D plot A 3-D plot shows the shows the
variations of variations of ffLEDLED(c,H). The (c,H). The
value is color value is color coded to show coded to show
iso-value iso-value lines. Seen lines. Seen from above, from above,
this is a map.this is a map.
CIE 2CIE 2ndnd Expert Symposium on LEDs Expert Symposium on LEDs430 440 450 460 470 480 490 500 510 520 530 540 550 560 570 580 590 600 610 620 630 640 650
10 nm
15 nm
20 nm
25 nm
30 nm
35 nm
40 nm
45 nm
50 nm
55 nm
60 nm
65 nm
70 nm
0%1%1%2%2%3%3%4%4%5%5%6%6%7%7%8%8%
7.50%-8.00%
7.00%-7.50%
6.50%-7.00%
6.00%-6.50%
5.50%-6.00%
5.00%-5.50%
4.50%-5.00%
4.00%-4.50%
3.50%-4.00%
3.00%-3.50%
2.50%-3.00%
2.00%-2.50%
1.50%-2.00%
1.00%-1.50%
0.50%-1.00%
0.00%-0.50%
ffLEDLED – Photometer 1 – Photometer 1
10.00
20.00
30.00
40.00
50.00
60.00
70.00
430.00 480.00 530.00 580.00 630.00
We can We can overlay a plot overlay a plot of FWHM vs. of FWHM vs. wavelength wavelength
for some for some modern LEDSmodern LEDS
We can We can overlay a plot overlay a plot of FWHM vs. of FWHM vs. wavelength wavelength
for some for some modern LEDSmodern LEDS
These would These would be measured be measured with <2% fwith <2% fLED.LED.
These would These would be measured be measured with <2% fwith <2% fLED.LED.
These would be measured These would be measured with <1% fwith <1% fLED.LED.
These would be measured These would be measured with <1% fwith <1% fLED.LED.
CIE 2CIE 2ndnd Expert Symposium on LEDs Expert Symposium on LEDs430 440 450 460 470 480 490 500 510 520 530 540 550 560 570 580 590 600 610 620 630 640 650
10
15
20
25
30
35
40
45
50
55
60
65
70
0%1%1%2%2%3%3%4%4%5%5%6%6%7%7%8%8%
7.50%-8.00%
7.00%-7.50%
6.50%-7.00%
6.00%-6.50%
5.50%-6.00%
5.00%-5.50%
4.50%-5.00%
4.00%-4.50%
3.50%-4.00%
3.00%-3.50%
2.50%-3.00%
2.00%-2.50%
1.50%-2.00%
1.00%-1.50%
0.50%-1.00%
0.00%-0.50%
ffLED LED – Photometer 2– Photometer 2
10.00
20.00
30.00
40.00
50.00
60.00
70.00
430.00 480.00 530.00 580.00 630.00
Photometer 2 has <1% fPhotometer 2 has <1% fLEDLED for most LEDs. for most LEDs.Photometer 2 has <1% fPhotometer 2 has <1% fLEDLED for most LEDs. for most LEDs.
But offers no significant But offers no significant improvement for these improvement for these
LEDs.LEDs.
But offers no significant But offers no significant improvement for these improvement for these
LEDs.LEDs.
CIE 2CIE 2ndnd Expert Symposium on LEDs Expert Symposium on LEDs430 440 450 460 470 480 490 500 510 520 530 540 550 560 570 580 590 600 610 620 630 640 650
10
15
20
25
30
35
40
45
50
55
60
65
70
0.00%0.50%1.00%1.50%2.00%2.50%3.00%3.50%4.00%4.50%5.00%5.50%6.00%6.50%7.00%7.50%8.00%
7.50%-8.00%
7.00%-7.50%
6.50%-7.00%
6.00%-6.50%
5.50%-6.00%
5.00%-5.50%
4.50%-5.00%
4.00%-4.50%
3.50%-4.00%
3.00%-3.50%
2.50%-3.00%
2.00%-2.50%
1.50%-2.00%
1.00%-1.50%
0.50%-1.00%
0.00%-0.50%
ffLED LED – Photometer 3– Photometer 3
10.00
20.00
30.00
40.00
50.00
60.00
70.00
430.00 480.00 530.00 580.00 630.00
Photometer 3 also has a wide range Photometer 3 also has a wide range of <1% fof <1% fLED.LED.
Photometer 3 also has a wide range Photometer 3 also has a wide range of <1% fof <1% fLED.LED.
But up to 7% fBut up to 7% fLEDLED
for these LEDs.for these LEDs.But up to 7% fBut up to 7% fLEDLED
for these LEDs.for these LEDs.
CIE 2CIE 2ndnd Expert Symposium on LEDs Expert Symposium on LEDs430 440 450 460 470 480 490 500 510 520 530 540 550
10
15
20
25
30
35
40
45
50
55
60
65
700.075-0.08
0.07-0.075
0.065-0.07
0.06-0.065
0.055-0.06
0.05-0.055
0.045-0.05
0.04-0.045
0.035-0.04
0.03-0.035
0.025-0.03
0.02-0.025
0.015-0.02
0.01-0.015
0.005-0.01
0-0.005
ffLED LED – Photometer 4– Photometer 4
10.00
20.00
30.00
40.00
50.00
60.00
70.00
430.00 480.00 530.00 580.00 630.00
Photometer 4 data has a limited Photometer 4 data has a limited wavelength range, but <1% fwavelength range, but <1% fLED LED
extends further into the blue extends further into the blue region than the others.region than the others.
Photometer 4 data has a limited Photometer 4 data has a limited wavelength range, but <1% fwavelength range, but <1% fLED LED
extends further into the blue extends further into the blue region than the others.region than the others.
And has fAnd has fLEDLED<3% <3%
even for these LEDs.even for these LEDs.And has fAnd has fLEDLED<3% <3%
even for these LEDs.even for these LEDs.
CIE 2CIE 2ndnd Expert Symposium on LEDs Expert Symposium on LEDs
ffLEDLEDLED batches
10
15
20
25
30
35
40
45
50
400 450 500 550 600 650 700
Peak Wavelength [nm]
FW
HM
[n
m]
To test the validity and To test the validity and usefulness of fusefulness of fLEDLED, ,
several batches of several batches of LEDs were measured.LEDs were measured.
To test the validity and To test the validity and usefulness of fusefulness of fLEDLED, ,
several batches of several batches of LEDs were measured.LEDs were measured.
Each batch included Each batch included similar LEDs in terms similar LEDs in terms of peak and FWHM, of peak and FWHM,
regardless of regardless of manufacturermanufacturer
Each batch included Each batch included similar LEDs in terms similar LEDs in terms of peak and FWHM, of peak and FWHM,
regardless of regardless of manufacturermanufacturer
The “central” LED in The “central” LED in each batch was used to each batch was used to
calibrate the calibrate the photometers for the photometers for the measurement of all measurement of all
other LEDs in the batch.other LEDs in the batch.
The “central” LED in The “central” LED in each batch was used to each batch was used to
calibrate the calibrate the photometers for the photometers for the measurement of all measurement of all
other LEDs in the batch.other LEDs in the batch.
Calibration Calibration LEDs shown LEDs shown
in blackin black
Calibration Calibration LEDs shown LEDs shown
in blackin black
CIE 2CIE 2ndnd Expert Symposium on LEDs Expert Symposium on LEDs
ffLEDLEDLED batches
10
15
20
25
30
35
40
45
50
400 450 500 550 600 650 700
Peak Wavelength [nm]
FW
HM
[n
m]
The spectra of each of The spectra of each of these LEDs is known, so these LEDs is known, so
we can calculate the we can calculate the error in measurement error in measurement
and hence the standard and hence the standard deviation for each batchdeviation for each batch
The spectra of each of The spectra of each of these LEDs is known, so these LEDs is known, so
we can calculate the we can calculate the error in measurement error in measurement
and hence the standard and hence the standard deviation for each batchdeviation for each batch
But the But the extent is extent is
not not 5 nm 5 nm like flike fLED.LED.
But the But the extent is extent is
not not 5 nm 5 nm like flike fLED.LED.
The smaller the spread in The smaller the spread in wavelengths, the lower the wavelengths, the lower the batch error. We can scale batch error. We can scale
the errors to a the errors to a 5 nm 5 nm region to compare directly region to compare directly
with fwith fLED.LED.
The smaller the spread in The smaller the spread in wavelengths, the lower the wavelengths, the lower the batch error. We can scale batch error. We can scale
the errors to a the errors to a 5 nm 5 nm region to compare directly region to compare directly
with fwith fLED.LED.
CIE 2CIE 2ndnd Expert Symposium on LEDs Expert Symposium on LEDs
ffLEDLEDCorrelation of Results for real LEDs to fLED
ALL photometers and ALL LED batches
0%
1%
2%
3%
4%
5%
0% 1% 2% 3% 4% 5%
fLED
Sta
nd
ard
De
via
tio
n o
f E
rro
rs i
n r
ea
l L
ED
ba
tch
es
[sc
ale
d t
o ±
5 n
m r
eg
ion
]
The blue line The blue line represents represents
equivalence.equivalence.
The blue line The blue line represents represents
equivalence.equivalence.
CIE 2CIE 2ndnd Expert Symposium on LEDs Expert Symposium on LEDs
ffLEDLED
ffLEDLED and and LEDs: and and LEDs:
ffLEDLED is specific to LED measurement. is specific to LED measurement. ffLEDLED is based on variations in spectral is based on variations in spectral
mismatch factors.mismatch factors. ffLEDLED reflects actual measurement procedures. reflects actual measurement procedures.
ffLEDLED agrees with results. agrees with results. ffLEDLED applies to all LEDs and photometers applies to all LEDs and photometers
investigated and is robust enough for future investigated and is robust enough for future developments.developments.
ffLEDLED and and LEDs: and and LEDs:
ffLEDLED is specific to LED measurement. is specific to LED measurement. ffLEDLED is based on variations in spectral is based on variations in spectral
mismatch factors.mismatch factors. ffLEDLED reflects actual measurement procedures. reflects actual measurement procedures.
ffLEDLED agrees with results. agrees with results. ffLEDLED applies to all LEDs and photometers applies to all LEDs and photometers
investigated and is robust enough for future investigated and is robust enough for future developments.developments.
CIE 2CIE 2ndnd Expert Symposium on LEDs Expert Symposium on LEDs
ffLEDLED
ffLEDLED and manufacturers: and manufacturers:
ffLEDLED helps in design of better photometers. helps in design of better photometers.
ffLEDLED does not require any more measurements does not require any more measurements than is currently done for calculation of fthan is currently done for calculation of f11’.’.
ffLEDLED can be calculated from limited range data can be calculated from limited range data – it does not require the full visible range.– it does not require the full visible range.
ffLEDLED should be calculated from data at 1 nm or should be calculated from data at 1 nm or smaller intervals.smaller intervals.
ffLEDLED and manufacturers: and manufacturers:
ffLEDLED helps in design of better photometers. helps in design of better photometers.
ffLEDLED does not require any more measurements does not require any more measurements than is currently done for calculation of fthan is currently done for calculation of f11’.’.
ffLEDLED can be calculated from limited range data can be calculated from limited range data – it does not require the full visible range.– it does not require the full visible range.
ffLEDLED should be calculated from data at 1 nm or should be calculated from data at 1 nm or smaller intervals.smaller intervals.
CIE 2CIE 2ndnd Expert Symposium on LEDs Expert Symposium on LEDs
ffLEDLED
ffLEDLED and users: and users:
ffLEDLED provides a much better selection criterion than f provides a much better selection criterion than f11’.’.
ffLEDLED is a property of the photometer, eliminating is a property of the photometer, eliminating
confusion on calibration requirements.confusion on calibration requirements. ffLEDLED allows for optimization of photometer selection allows for optimization of photometer selection
across all the user’s LED requirements.across all the user’s LED requirements.
ffLEDLED gives an indication of errors in measurement. gives an indication of errors in measurement. Advances in quality of photometers and better Advances in quality of photometers and better
selection will reduce uncertainties in measurement.selection will reduce uncertainties in measurement.
ffLEDLED and users: and users:
ffLEDLED provides a much better selection criterion than f provides a much better selection criterion than f11’.’.
ffLEDLED is a property of the photometer, eliminating is a property of the photometer, eliminating
confusion on calibration requirements.confusion on calibration requirements. ffLEDLED allows for optimization of photometer selection allows for optimization of photometer selection
across all the user’s LED requirements.across all the user’s LED requirements.
ffLEDLED gives an indication of errors in measurement. gives an indication of errors in measurement. Advances in quality of photometers and better Advances in quality of photometers and better
selection will reduce uncertainties in measurement.selection will reduce uncertainties in measurement.
CIE 2CIE 2ndnd Expert Symposium on LEDs Expert Symposium on LEDs
AcknowledgementsAcknowledgements
Thanks to NIST and Lumileds.Thanks to NIST and Lumileds. For the great quantity and quality of data provided For the great quantity and quality of data provided
by them.by them.
Thanks to all the members of CIE TC2-45 and Thanks to all the members of CIE TC2-45 and
TC2-46.TC2-46. For their useful input and discussions.For their useful input and discussions.
Special thanks to Yoshi Ohno, NIST.Special thanks to Yoshi Ohno, NIST. For all his help.For all his help.
Thanks to NIST and Lumileds.Thanks to NIST and Lumileds. For the great quantity and quality of data provided For the great quantity and quality of data provided
by them.by them.
Thanks to all the members of CIE TC2-45 and Thanks to all the members of CIE TC2-45 and
TC2-46.TC2-46. For their useful input and discussions.For their useful input and discussions.
Special thanks to Yoshi Ohno, NIST.Special thanks to Yoshi Ohno, NIST. For all his help.For all his help.