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1. The LED Luminaires Lumen Test Difference at Integrating
Sphere and Goniophotometer
As well as we know that for the LED luminaires lumen test, the CIE121: 1966 Clause
6.1, CIE127-2007 Clause 6.2 and IES-LM-79-08 Clause 9.0 are mentioned two luminous
flux test method: the first is adoption integrating sphere+photometer or
spectrometer(recommend by CIE121: 1966 Clause 6.1.1, CIE127-2007 Clause 6.2.and
IES-LM-79-08 Clause 9.0), this kind of test method is relative measurement method on
lumen test; the second is photometric method which is adoption goniophotometer, this
kind of test way is absolute measuring method. If adoption integrating sphere and
photometric method to test same one LED lamp, we will find luminous flux data of two test
method have big difference. This article is mainly discuss luminous flux test difference at
integrating sphere and goniophotometer.
The principle of integrating sphere measuring total luminous flux by calibrated
standard lamp. Due to there will be use a calibrated standard lamp, so there’s no need to
know the integrating sphere’s output luminous flux, we can calculate the SSL product’s
luminous flux by compare with standard lamp. Generally speaking, the integrating sphere
test method suitable for small size LED lamp to measuring lumen and color parameters,
this is lumen relative test method, moreover, the integrating sphere test method have
quick test speed and it needn’t dark room advantages etc. Normally, if lamp size is small
or like single LED, the test result and accuracy will be much better.
If adoption integrating sphere method testing big size LED luminaires, it have some
better disadvantages compared with photometric method. When use integrating sphere
test LED luminaires, there have a fact that the LED luminaires have different types, such
as single LED, LED bulb, LED luminaires and others, the type of LED luminaires have big
influence for final total luminous flux measurement. Meantime, integrating sphere test
method need to do calibration procedure. Normally, if test LED luminaires, the standard
lamp have to keep same emission characteristics with tested LED luminaires, the
standard lamp adoption white LED will be best way. Of course, other type lamp also can
used as standard lamp, but the test accuracy will be impacted. The test way will bring
some difference, usually we use the 4π test way to test a lamp which emitting the lighting
at 360° direction and the tested lamp should be placed in the centre position of the
integrating sphere(recommend by IESLM-79-08 Clause 9.2.5). This is the best way to test
LED luminaires; if the tested luminaries emitting the lighting at fixed direction, such as
LED panel, LED street light or others, we need use 2π test way which means test the
luminaries should be mounted on the one side of integrating sphere(recommend by
IESLM-79-08 Clause 9.2.5). For the 4π test way; if the tested luminaries output power is
too big or the the lamp shell have large size, there will be happen self-absorption effect
more or less, then we need to use a auxiliary lamp(recommend by IESLM-79-08 Clause
9.1.5) to avoid the error. Generally speaking, the integrating sphere method is suitable for
the compact LED and small size LED lighting. The test result of the luminaries flux can be

2. achieve high accuracy and stability by this way; if use integrating sphere testing large size
LED luminaries, the integrating sphere method have obviously defect, this time, the the
luminaries flux data is not accurate and stable.
Adoption goniophotometer measuring total lumen which is photometric method, and
this way have small limitation on the lumen test. The test principle of photometric method
is use goniophotometer measuring all direction’s intensity distribution (or show the
illuminance of light source at limited distance), through collection the intensity data at
different direction to calculate the total lumen. Compared with the integrating sphere
method, due to the difference of test light source’s intensity distribution, the photometric
method don’t exist error in the theory, as the photometric method is absolute test method
on the lumen test. It doesn’t need calibrated total luminous flux standard lamp, but it need
longer test time for each sample. The photometric method which will adoption
goniophotometer device, and there will be mentioned the type C
Goniophotometer(recommend by IES-LM-79-08 Clause 9.3.1 and CIE121:1996 Clause
3.2 etc), dark room, test distance(mentioned by IES-LM-79-08 Clause 9.3 and
CIE121:1996 Clause 6.2.1.4).
The difference of testing total lumen output consist of type of goniophotometer, test
method(CIE121: 1996 Clause 3.4.2, Clause 3.4.1 and Clause 3.4.3), test distance and
detector level etc. According to different type of LED luminaires, we can adjustment the
relevant test method or testing device, such as if tested luminaires belong to narrow beam
angle SSL product, we can use compact goniophotometer; selection Type C
Goniophotometer, adjust test distance, choose higher level Class L detector(detector
details classification description here: http://www.lisungroup.com/article-id-70.html) which
can help achieve high precision measurement. In the practice testing, the photometric
method can achieve luminous flux data’s highest measurement, due to some limitations
inherent of integrating sphere test method, it's impossible to remove the test tolerance, the
only we can do is try best to reduce the test tolerance; but for the photometric method,
there almost haven't too much limitations and we can replace the test instrument,
adjustment system configuration and change test method to fix this test tolerance.
As explained above, the most simple way to measuring LED luminaires luminous flux
is adoption integrating sphere and photometric meter, this way is meet visual flux spatial
demand, we can use a fixed front-end photometric meter to measure the total flux and the
test time is fast and convenient. By comparison with a standard light source which keep
have similar spatial and spectral distribution characteristics of tested luminaires to
measuring luminous flux, so this way will be need use a calibrated standard lamp.
Comparing with goniophotometer, the integrating sphere and photometric meter have high
test speed, but when tested LED luminaires have different spatial intensity distribution
characteristics from standard lamp, it's easy to cause test tolerance. This kind of test
tolerance is hard to fix, so it should be adoption use a good design geometry integrating
sphere and use standard LED standard lamp which have similar emission characteristics
with tested LED luminaires to reduce this error.
As mentioned previously, if the shape of tested lamp is similar with tested luminaires,
then the integrating sphere method will have better test accuracy. When measuring
luminous flux, for the LED bulb, small size LED luminaires and tube which beam angle

3. more than 180°, we should adoption integrating sphere and spectrometer to do 4π test.
As for the big size LED panel, LED street lamp and traffic lamp which beam angle less
180°, if need adoption integrating sphere method, then the integrating sphere should have
side opening structure to do 2π test or use auxiliary lamp for assistance test, but this way
have complex test procedure and test result is uncertainty. For these small beam angle
luminaires, the best way is adoption goniophotometer method and working on the dark
room, this can make sure high accuracy. But when adoption goniophotometer method, we
have a clear understanding for test difference of different test method. Normally, like the
LED panel, the best test method is C-γ; for the traffic lamp and spotlights will choose B-β
test. At the same time, both test methods are need at dark room environmental,
comparing with integrating sphere, the goniophotometer need more professional test
environmental and professional engineer. In summary, the measurement principle,
environment and test methods of the integrating sphere and the distributed spectrometer
are different, and the measurement results are not comparable. We can choose the right
way to test according to different standards and different requirements.
In summary, both integrating sphere and goniophotometer method have different
measuring principle, environmental and testing methods, the both measurement results
are not comparable. We can based on different standards and requirements to selection
suitable test way.
In order to better compared test result, we used the spectrometer, integrating sphere
and goniophotometer to testing LED bulb and street lamp. The test report as below, we
can refer this.