LG-2.0
Mirror Goniophotometer
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LG-2.0 Mirror Goniophotometer for Luminaires
Theory of Operation
A goniophotometer (also called a distribution photometer) is a device for measuring the luminous
intensity distribution of luminaires. In other words, what this means is that the intensity of the light
emitted by a light fitting is measured as a function of angle all around the fitting. This data is
stored electronically. From the data a test report can be produced which outlines the performance
of the light fitting.
Additionally, the data can be fed into lighting layout design software, to simulate lighting scenarios
and predict information such as:
•
•
•
How many luminaires it will take to provide sufficient lighting in a room, and therefore which is
the most cost-effective or energy-effective;
Whether a proposed streetlighting design will
produce enough pavement luminance and
with sufficient uniformity;
The best flood-lighting arrangement for a
sports stadium; etc.
The word goniophotometer has three word
stems:
•
Gonio – meaning angles;
• Photo – meaning light; and
• Meter – meaning measure.
So the term goniophotometer simply means a device for measuring light at different angles. We
can also break this up into two main parts: a goniometer for measuring the angles and a
photometer for measuring the amount of light.
To measure the distribution of light from a luminaire, a long test distance is used – usually between
15 and 25 meters. The luminaire is positioned on the goniometer at one end of a long room and
the photometer is at the other end.
One of the problems with photometric
measurement is that for many types of lamps,
the amount of light emitted by the lamp changes
when it is tilted.
This means that when
measuring a luminaire it must stay mounted in its
normal burning position. But how, then can we
measure the light that comes out beneath it
when the detector is across the other side of the
room?
The answer to this is to use a mirror to reflect the
light from the fitting onto the photometer head.
By rotating a mirror around the luminaire, the
amount of light coming out at different tilt angles can be measured. And by rotating the luminaire
about its axis the light distribution all around the luminaire can be measured, without tilting it and
with the detector remaining in a fixed position. This is shown schematically on the following page.
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LG-2.0 Mirror Goniophotometer for Luminaires
Schematic of Measurement
The LG-2.0 is a CIE type C/γ goniophotometer. The diagrams on this page indicate how the
system measures the light from different angles around the luminaire.
Side View
The diagrams on the right show how the mirror rotates about a
horizontal axis around the luminaire to reflect the light from
different vertical angles on to the photometer.
These vertical angles are called elevation angles or gamma
angles. They are symbolised by the Greek letter γ in a CIE C/γ
coordinate system.
C/γ (CIE)
C/γ (IES)
Top View
The diagrams on the left show how the luminaire is
rotated about its own (vertical) axis to present different
C-planes towards the photometer via the mirror.
These cross-sections through the luminaire are called
azimuth angles or C-planes. They are symbolised by
the letter C in a CIE C/γ coordinate system.
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LG-2.0 Mirror Goniophotometer for Luminaires
Goniometer
The mirror is supported on a tower and rotates on an arm about a horizontal axis. The test item is
mounted on an arm on a separate tower and rotates about a vertical axis. The two towers are
rigidly fixed and very stable, and the mirror is counterbalanced.
One of the problems with some
On both axes are highest quality harmonic drives and absolute goniophotometers is that they move
angular encoders. This gives the system extremely powerful the mirror too fast while measuring. If
the mirror is moving at 6 RPM and a
control over the motion and permits excellent angular accuracy.
The luminaire arm can be raised and lowered to cater for
different types and sizes of test items. Because the luminaire is
mounted on a separate tower than the mirror, the vertical travel
can bring the luminaire down very close to ground level, which
means that the operator can easily attach and detach luminaires
without needing to stand on a ladder or have a special
laboratory room preparation. The luminaire arm can also be
inverted under software control to switch between base up and
base down burning positions. The switching between positions
is fully motorised and only takes a few seconds, which means
that this eliminates any possible operator human error.
50 Hz source is being measured, then
in one line power cycle (20 ms) the
mirror actually moves more than 0.7°.
This makes it impossible to keep a
0.1° angular accuracy.
The speed of the LG-2.0 mirror during
testing is carefully controlled to be as
fast as possible for the light source
being measured. A typical interior
luminaire test takes only 5-8 minutes,
which is insignificant compared with
the luminaire mounting and warm-up
time (sometimes > 1 hour for LEDs)!
The LG-2.0 incorporates safety features such as multiple emergency stops and an emergency cutoff circuit that prevents the operator from re-activating the system while it is in error mode. The
surface finish of the metalwork is impeccable and the elliptical mirror also has a much sleeker and
better quality look than the other mirror shapes like rectangular and octagonal.
Photometer
The PH-1L Photometer consists of a photometer head (photocell) and a multiranging amplifier with
built-in data acquisition. The photometer head is very well V (λ) corrected, with f1’ < 1.50%. This
means that a special filter is placed over the top of the detector
LEDs are often very directional, which
so that its spectral response closely matches the spectral means that long test distances are
response of the human eye in normal lighting conditions. In required before the inverse square rule
other words, the photometer head is seeing what we would see! of photometry applies. CIE 121
recommends a test distance of at least
Also, the photometer head has built-in temperature stabilisation 15 times the size of the test item, ie:
and is well baffled to protect against stray light affecting the 24 metres for a 1.6 metre luminaire,
which is why we recommend a 25
measurements.
metre test distance. PSI’s LG-2.0
The amplifier uses a proprietary digitisation methodology that goniophotometer has a resolution of
than 1 millicandela (0.001 cd) at
produces incredibly accurate and stable results, and it is better
a test distance of 25 metres!
sensitive enough that we can achieve better than one microlux
resolution. Our technology used in the photometer system is now used by so many laboratories
around the world including government national measurement institutes such as PBT Germany,
which is perhaps the most technically accomplished photometric laboratory in the world.
Spectroradiometer
With our SP-3C spectroradiometer interfaced with the LG-2.0 goniophotometer it is possible to
perform goniospectroradiometric tests to standards such as IES LM-79. The system can measure
the spectrum of the light source at different angles and calculate derived data such as: (x,y)
coordinates; (u’,v’) coordinates; correlated colour temperature (CCT); colour rendering index (Ra);
colour spatial uniformity (∆u’v’); dominant wavelength; etc. The SP-3C is sensitive enough that it
can accurately measure the spectrum of light sources as little as 1 cd at a distance of 25 metres.
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LG-2.0 Mirror Goniophotometer for Luminaires
Control Software
The software that comes with the system is in two parts: control software and report generation
software. The big advantage of dividing the software into these two categories is that the report
generation software can be installed onto other PCs so that reports can be produced while other
measurements are being performed. All software is Windows 7 compatible.
The control software has the flexibility to give the operator all of the
control needed, and is not restrictive and rigid. Features include:
•
Easy-to-use operation what works like a software “Wizard” in a
step-by-step process so the measurement is straightforward;
•
Relative (cd per 1000 lm) or Absolute measurement modes;
•
Ability to specify test angles and angular increments, as small
as 0.1° in both axes; regular angles or user-specified;
•
Ability to take measurements “on the fly” without stopping;
•
Ability to select from a range of coordinate systems, ie:
o Type C/γ for luminaires;
o Type B/β for floodlights;
o Type A/α for signals and automotive test items;
•
Standard test routines, eg: IESNA and CIE roadway
test angles for streetlights and NEMA classification
test points for floodlights;
•
Bare lamp luminous flux measurement, and ability to
store lamp data in a database for easy management;
•
Display of luminous intensity distribution real-time
while performing the measurement;
•
Facility for monitoring the stability of test items;
•
Joystick control to move to different arbitrary angles;
•
Ability to set multiple calibrations, which are then
selected according to lamp or LED type;
•
Diagnostic and troubleshooting function;
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Ability to select the integration time for the
measurement or use a smart ‘Auto-detect’ function,
to allow for measurement of different frequency AC
sources or pulsed LED devices;
•
Stray light subtraction, by executing a complete test
with a mask in front of the test item to measure the stray light at each test point, then repeating
the test with the mask off and subtracting the stray data at each point.
Additionally, we supply a wireless, remote hand-held control that enables the operator to control
the goniometer from anywhere in the laboratory. Coupled with the secondary monitor on the
laboratory wall that displays important test information such as the luminous intensity and the
goniometer angles, the operator has incredible flexibility and assistance for aligning test items.
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LG-2.0 Mirror Goniophotometer for Luminaires
Report Software
The report generation software, PhotometricCentre, is also flexible. The user can select which
pages are to be included in a report so that the report may be customised according to each
client’s needs. Fixed report generators that have a standard format for each type of test item are
too restrictive. Features of our report generation software include:
• Ability to customise contact details and logo which appear on the printed pages;
• Ability to select which pages, charts and diagrams appear in the printed report;
• Test details with uncertainties of measurement;
• Polar curves and H-V plots – with ability to zoom in on lowest 10% regions to study spill-light;
• Photometric solid – 3D projection;
• IsoCandela diagrams – Azimuthal projection format for C/γ and H-V format for A/α and B/β;
• IsoLux diagrams in 2D or 3D web format, shaded or line contour, plus greyscale;
• Average luminaire luminance table;
• Luminous flux summary table; Zonal lumen density; Lumen pie chart and Zonal flux diagram;
• Tables of coefficients of utilisation – both the IESNA and CIBSE TM5 formats;
• Utilisation factor diagrams for streetlights;
• Glare rating: Luminance limiting curves; UGR Tables (Full and Reduced); CIBSE LG3 rating;
• Ability to display a digital image of the test item in the report for easy identification;
• Streetlight performance parameters – throw, control and spread plus IESNA roadway diagram;
• Ability to export derived data: charts and diagrams as .bmp or .jpg images; tables as .csv files.
In addition to the control and report generation software, other photometric software utilities can be
provided to perform such tasks as:
•
PhotometricFileEditor: Post-processing of the photometric data: edit, modify and manipulate
the measured data, plus convert between IES, CIE, EULUMDAT & TM14 file formats;
•
PhotometricBrowser: View preview polar curves of all the IES files in a directory, select one
or many and then display them simultaneously on the same graph for comparison;
•
PhotometricCatalogue: View and export additional charts and diagrams derived from the
measured data for use with product catalogues;
•
PhotoLux: Perform lighting layout design simulations using the measurement data; includes
both interior and exterior, sports fields, roadways, building façades.
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LG-2.0 Mirror Goniophotometer for Luminaires
IESNA LM-79-08 Functionality
The LG-2.0 goniophotometer maintains the luminaire in its designed burning position, thus it
complies with the IES LM-79 for goniophotometry of LEDs and Solid State Lighting (SSL) devices.
The system also measures the Luminous Efficacy and the software outputs the Zonal Lumen
Density for various angular ranges, as required by some Energy Star standards.
With the addition of a spectroradiometer such as PSI’s SP-3C Real-time Spectroradiometer, the
system can then measure the spatially-averaged Chromaticity Coordinates and Correlated Colour
Temperature, and can calculate the Colour Spatial Uniformity which is also required by some
Energy Star standards.
In addition to LM-79, the LG-2.0 also complies with other international standards such as:
•
•
•
•
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CIE 121 “Goniophotometry of Luminaires” and its supplements
CIE 84 “The Measurement of Luminous Flux”
CIE 70 “The Measurement of Absolute Luminous Intensity Distributions”
CIE 43 “Photometry of Floodlights”
EN 13032-1; IES LM-10, LM-31, LM-35-02, LM-41, LM-46-04, LM-75-01, LM-80-08.
Traceability
We can provide traceability to NMIA (Australia), NIST (USA), PTB (Germany), NPL (UK) and other
countries including China, Korea, Malaysia, Taiwan, India, Thailand.
Key Specifications
Model No.:
Max Test Item Luminous Dimensions:
Max Test Item Physical Dimensions:
Max Test Item Weight:
Angular Resolution:
Angular Accuracy:
Resolution – illuminance:
Resolution – luminous intensity*:
Resolution – luminous flux *:
LG-2.0
1.6 metres
1.8 metres
50 kg
0.001° (luminaire), 0.01° (mirror)
< 0.1° (luminaire), < 0.1° (mirror)
1 microlux (0.000001 lx)
1 millicandela (0.001 cd)
10 millilumens (0.01 lm)
* For a 25 metre test distance
Client List
Clients who have purchased an LG-2.0 system include:
• CDC Lighting, Thailand;
• Czech Metrology Institute, Czech Republic;
• Rooster Lighting, Taiwan;
• Everlight Lighting, Taiwan;
• Korea Institute of Lighting Technology (KILT), Korea;
• LG Electronics, Korea;
• SIRIM QAS International Sdn Bhd, Malaysia;
• Tae Yang Lighting, Korea;
• Taiwan Electrical Research and Testing Centre (TERTEC), Taiwan;
• Thai Industrial Standards Institute (TISI), Thailand;
• Vinic Lighting, Thailand.
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Photometric Solutions International Pty Ltd
Factory Two, 21-29 Railway Ave
Huntingdale, Vic, 3166, Australia
Tel: +61 3 9568 1879, Fax: +61 3 9568 4667
Email: [email protected]
Web: http://www.photometricsolutions.com
ABN 34 106 665 141
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