1. Photometry of LED Lighting Devices
Tony Bergen

2. Contents Introduction – Specific Issues with LEDs IES LM-79-08
Current CIE Activities

3. Introduction – Specific Issues with LEDs
Introduction – Specific Issues with LEDs* * And solid-state lighting devices in general

4. What’s good? Long lifetime Robust “Tuneable” colours
(Becoming) highly energy efficient

5. What’s not so good? Output is very temperature dependant
Poor design gives shorter life
Issues with luminance/glare
Good photometry is harder

6. Photometric Challenges
Quasi-monochromatic spectra means good quality photocells are more important than ever …

7. Photometric Challenges
Pulse-width modulated light causes timing and measurement issues
Long stabilisation time
Ambient temperature sensitivity
Absolute photometry instead of Relative (cd/klm)

8. Photometric Challenges
Directionality of light output of LEDs can cause inverse-square law to fail at shorter test distances …

9. Inverse-Square Law
Eg: Divergent LEDs on a linear luminaire

10. Inverse-Square Law Consider a 1200 mm luminaire
measured at 6 metres (5 : 1)
Beam incorrectly measured
Inverse square law doesn’t apply
 I  E x d2

11. Photometric Challenges
Sometimes need to use CIE recommendations* for floodlight photometry to calculate required test distance * CIE Publication no. 43 “Photometry of Floodlights”

12. IES LM-79-08 Electrical and Photometric Measurements of Solid-State Lighting Products

13. IES LM-79-08 Specification released in 2008
Extra-special consideration given to:
Ambient (environmental) conditions
Spectral properties
Thermal characteristics
Gives guidelines for measurement in integrating sphere and goniophotometer

14. Integrating Sphere Photometry
Sphere with inside diffuse, high reflectance white
Light output from test lamp is compared with light output from reference (known) lamp
Measure luminous flux, luminous efficacy and spatially-averaged chromaticity

15. Integrating Sphere Photometry
LM-79 says:
Two geometries (also specified by CIE 84):
4 (full sphere)
2 (hemisphere)

16. Integrating Sphere Photometry
For 2 geometry, plug the gap or have a darkened room behind
If plugging the gap, make sure that the cover disk doesn’t extract heat from the device

17. Integrating Sphere Photometry
LM-79 suggests two methods of measurement:
Sphere-photometer uses a traditional photocell and picoammeter or equivalent (beware spectral mismatch)
Sphere-spectroradiometer uses a spectro to measure both flux and chromaticity (recommended method)

18. Integrating Sphere Photometry
Match reference lamp and test lamp as closely as possible
Make sure the internal temperature is within 25° ± 1°C
Calculate spectral mismatch correction factors if necessary
LM-79 slightly more relaxed on sample size for given sphere size than CIE 84

19. Goniophotometry
A goniophotometer measures luminous intensity distribution and chromaticity distribution
Can derive luminous flux etc.
Has advantage of being absolute measurement

20. Goniophotometry LM-79 says:
Make sure test distance is sufficiently long so that the inverse square law applies
Make sure test angle increments are sufficiently small to make measurement accurate
Keep room temperature within 25° ± 1°C
Calculate spectral mismatch correction factors if necessary

21. Goniophotometry Measure chromaticity:
In steps of 10° in elevation angle
In two orthogonal C-planes 0° and 90°
Calculate spatially-averaged chromaticity, weighted by:
Luminous intensity in each direction
Solid angle

22. Spatial non-uniformity of chromaticity
Deviation of chromaticity from spatial avg

23. Spatial non-uniformity of chromaticity
Deviation of chromaticity from spatial avg
Spatially averaged colour temperature = 5870K

24. Spatial non-uniformity of chromaticity
Deviation of chromaticity from spatial avg
Spatially averaged coordinates: u’ = , v’ =

25. Current CIE Division 2 Activities

26. TC2-50
Measurement of the Optical Properties of LED Clusters and Arrays
This is the main standard that we want to see completed
It will cover similar aspects to the IES LM-79-08
Has been held up in the past due to arguments over definitions and changed chair twice
From Budapest meeting 2009 we now have a promising way forward

27. TC2-58 Measurement of LED Radiance and Luminance
This is a difficult area of measurement because LEDs are small and directional
Some similarities with laser safety

28. TC2-63 Optical measurement of High-Power LEDs
CIE 127 “Measurements of LEDs” already covered low power LEDs
This standard will look at measurement of individual high power LEDs, as opposed to LED clusters and luminaires

29. TC2-64 High speed testing methods for LEDs
Looking into test methods for production-line testing of LEDs
Want to make measurements consistent and comparable between labs

30. TC2-66 Terminology of LEDs and LED Assemblies
This TC is looking in to terminology for different types of LEDs and LED packages
Will be used to create appendices for the TC2-50

31. TC2-65 Photometric measurements in the mesopic range
This is important for photometry of street lighting luminaires where their application will often be in the mesopic range
The mesopic range favours white LED sources compared with traditional HPS streetlights

32. Reporterships R2-42 Measurement for LED Luminaries
R2-43 Measurement of Integrated LED Light Sources
R2-44 Photometric Characterisation of Large Area Flat Sources used for Lighting

33. Thank you for your kind attention
Tony Bergen
Technical Director
Photometric Solutions International
Factory Two, Railway Avenue
Huntingdale, Vic, 3166, Australia
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