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Light Intensity Unit

Working Group 4.12

Profile

The working group is responsible for the realisation, maintenance and dissemination of the physical measurement quantity luminous intensity and its SI unit, the Candela, as well of its derived quantities illuminance and luminance. With the help of suitable transfer standards (light sources or measurement devices) the units and the photometric responsivity of calibrated measurement devices, respectively, are dissiminated to customers from industry and science. The traceability of new measurement methods in the field of photometry as well as the development of new transfer standards for innovative (e.g. LED-based) lighting is part of its business. Strong collaboration in national and international bodies and committees are used to exert influence in photometry and radiometry.

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Research/Development

Characterisation of novel light sources

Besides lifetime, aging behaviour, spectrum of light and colour of light, the electrical and photometrical data are crucial for the assessment of the suitability of light sources for general lighting. Traceable measurements used to validate algorithms of manufacturers used for proficiency testing of their products during the production process create confidence in labelling and assist manufacturers in the product development.

New measurement methods

The development of novel photometers combined with laser-based spectral characterization enables PTB to reduce measurement uncertainties of the realised SI Base-Unit Candela. The investigation of measurement uncertainties of measurements where novel measurement devices (like array-spectroradiometers, Imaging Luminance Measuring Devices (ILMD)) and new measurement techniques (like near-field goniophotometry) are used, is one of the tasks where collaboration with other working groups of PTB and with measurement device manufacturers are focused on.

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Services

Calibration

The calibration of transfer standards for traceability to national units for the photometric measurands luminous intensity, illuminance and luminance is routinely provided.

Committees

Active collaboration in national and international committees (like Opens external link in new windowCIE, Opens external link in new windowDIN, Opens external link in new windowISO, Opens external link in new windowCEN, Opens external link in new windowEURAMET und Opens external link in new windowCCPR) aiming at the creation of standards and recommendations helpful for the society is perceived as a service to the society.
Opens external link in new windowCommittee work

Accreditation/Survey

The working group supports the Deutsche Akkreditierungsstelle (Opens external link in new windowDAkkS) to survey calibration laboratories for photometric and colourimetric quantities and characteristic numbers.

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Information

Photometer bench

 

  • The more than 40 m long photometer bench can be separated by gates and used individually.
  • Three transverse benches, Y-bench-system and lamp turning device, to mount calibration goods, transfer standards and measurement devices.
  • Two lamp houses with high power lamps (halogen lamp, for illuminant A up to 20 klx; HMI, for day-light application, up to 100 klx)

 

Integrating sphere photometer

  • Two spheres with a diameter of 1.5 m and 2.5 m.
  • Coatings made of barium sulfate (BaSO4) with ρ = 0.87 bzw. ρ = 0.95, respectively.
  • Lock-in technique for auxiliary lamp available.

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