Stable laboratory DC-power supplies are utilized for supplying the operating current or voltage for the devices in the ageing bench. The photometric / radiometric performance of the artefacts, as well as the temperature and current / voltage of the artefacts are monitored.
The electrical and photometric / radiometric performance of each artefact shall be measured after the initial seasoning and after every 2000 h of ageing. Regarding the measurements, the general conditions of IES LM-79 and IEC 62922 apply, unless otherwise specified. The parameters to be measured for each artefact on each measurement round include the following, in this order:
o Ambient temperature (°C)
o Relative humidity (% R.H.)
o Artefact temperature (°C)
o DC-current (A) and forward voltage (V)
o Total luminous flux (lm)
o Relative spectral radiant flux
Chosen artefacts include OLEDs. Due to the possibility of black spots that can form during the operation of OLEDs, the luminance or spectral radiance output of the panels shall be measured for possible changes.
An initial seasoning of 100 hours is applied for all products before applying an accelerated ageing stress given below:
· High Temperature Operating Life test (HTOL);
· Temperature and humidity stress (damp-heat);
· Electrical stress;
· UV exposure stress.
It is agreed, that the main output parameters (luminance, luminous flux, colourimetric parameters, voltage, current) will account for the lifetime determination as relative parameters and the operating ageing parameters (current, voltage, junction or board temperature, humidity) will account for the lifetime determination as absolute parameters.
Realizations at NMIs:
1. Natural ageing
Natural ageing at VTT, National Metrology Institute of Finland
Natural ageing setup at LNE, National Metrology Institute of France
2. Accelerated ageing
UV setup at TÜBİTAK UME, National Metrology Institute of Turkey
Accelerated ageing setup at LNE, National Metrology Institute of France
First results of both „natural ageing“and „accelerated ageing“tests will be presented during the final Stakeholder workshop in May 2017 in METAS, Wabern (refer to Final Stakeholder Workshop).
All the ageing data will be obtained by end of the project, analysed and reported in terms of reports and publications.