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Photometry

Working Group 4.15

Profile

The working group 4.15 directs their focus on the realization and dissemination of photometric units for the luminous flux and related quantities like distribution temperature, correlated color temperature and colorimetric quantities like chromaticity coordinates for almost all light sources. Common light sources are incandescent lamps, discharge lamps, white and monochrome LEDs, but also organic LEDs can be used as transfer standards. The close collaboration with industry and other NMIs over the last decades allows continuous improvement and further development of the measurement systems and methods used.

Other tasks include:

  • consulting of the industry to metrological issues
  • supporting industry in the development of transfer standards (e.g. LED based transfer Standards)
  • carrying out verifications for example as assessors for the DAkkS (German Accreditation Body)
  • participation in international comparisons within the CCPR, EURAMET and other associations

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Research/Development

The principle of goniophotometry is independent of the technical realizations of the different types of goniophotometers. A goniophotometer measures the illuminance  E(r,θ, φ) on a closed envelope around a lamp measured with a V(λ)-matched photometer for all directions (θ, φ) of emission within the full solid angle (4π sr).
For this task necessary measurement systems are developed, used and improved at PTB over more than 50 years [1]. Highlights of this development are the robot goniophotometer currently used [2] (Fig. 1) and the new LED goniophotometer (Fig. 2) for the calibration of LED transfer standards with higher mass (mmax ≈  15 kg).

 

Abbildung 1: Roboter-Goniophotometer

 

Abbildung 2: LED-Messplatz

 

In the field of unit dissemination via LEDs the workgroup 4.15 develops regularly suitable LED transfer standards in the range of a few lumen up to some kilolumen. Solid-state lighting products are still developing rapidly, so that in addition to traditional LED transfer standards for the luminous flux new transfer standards with the ability to vary spatial, spectral and temporal properties combined in one device are under development. A first transfer standard like this was designed and manufactured and is currently in the test phase within the "EMRP ENG62 MESaIL" project.

[1] PTB-Mitteilungen, Heft 4, 2015, pages 18-30 and 31-38
https://www.ptb.de/cms/fileadmin/internet/publikationen/ptb_mitteilungen/mitt2015/Heft4/PTB-Mitteilungen_2015_Heft_4.pdf
[2] Robot Goniophotometry at PTB, Metrologia 52, pages 167-194, Bristol, UK
http://iopscience.iop.org/article/10.1088/0026-1394/52/2/167/pdf

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Services

  • Photometric / Colorimetric calibrations
  • Goniophotometry / Goniospectroradiometry /Goniocolorimetry for medium-sized light sources up to 2 m length
  • Measuring operation of the robot goniophotometer (measuring diameter up to 6 m) for photometric measurements and in neighboring UV and IR spectral regions
  • Goniophotometry / Goniospectroradiometry / Goniocolorimetry for LEDs
  • Study of radiation characteristics of LEDs

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Information

Robot-Goniophotometer

Quantity CharacteristicRange
luminous flux Φ5 lm < Φ < 1 000 000 lm
measurement distance d1 m < d < 2,75 m
lamp mass mm < 23 kg
measureable solid angle Ω0 sr < Ω < 4π sr
standard wavelength range spectrometer 360 nm ≤ λ ≤ 830 nm

 

LED Goniophotometer II

Quantity CharacteristicRange
luminous flux Φ0.200 lm < Φ  < 50 000 lm
luminous intensity I0.020 cd <  I  < 4 000 cd
measurement distance d

0.1 m < d  < 1 m  (left part)

0.1 m < d  < 3 m  (right part)

LED mass m

m  < 500 g  (left part)

m  < 10 kg  (right part)

measureable solid angle Ω0 sr < Ω  < 4π sr
wavelength range spectrometer 1360 nm ≤ λ ≤ 830 nm
wavelength range spectrometer 2750 nm ≤ λ ≤ 1050 nm

Both parts of the LED goniophotometer II (left and right) are sharing the same photometers and spectrometers input optics mounted on a turnable wheel. There are also unfiltered silicon detectors (radiometer) available to measure radiant intensity and radiant flux. A third spectrometer with a spectral range below 360 nm is in preparation to measure LEDs in the UV range in future.

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