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Light and colour of displays

Displays are key components for visual information switching. With the advance of the display technique – from organic light emitting diodes to semiconductor lasers to micro mirror arrays –, the metrological requirements for the determination of the most important characteristics and simultaneous reduction of the uncertainty of measurement are increasing. So the new measuring facility of the PTB is used to develop measuring procedures and to optimize transfer standards adapted to the specific properties of modern display structures.

Circular robot for the displacement of a photometer or spectroradiometer in the hemisphere in front of a display for the determination of the values of photometric and colorimetric characteristics and their angular dependence. Plotted is also the luminance as a function of the viewing angle, measured in a horizontal plane in front of a “white-controlled” display (TFT display of a laptop), with strongly decreasing “brightness” at the edge of the viewing area.

At the PTB a display measuring assembly has been developed using the arm of a circular robot to align photometric and colorimetric measuring instruments to the display and to displace them in the hemisphere in front of it. The arm has four rotation axes and allows measurements with radii up to 0,8 m for which any position or path can be selected. With a luminance measuring device or a compact CCD spectroradiometer, the mean values of the luminance and of the relative spectral distribution are measured for the partial areas as a function of angle. From these, colour dot coordinates, colour saturation and most similar colour temperature as well as luminance and colour contrasts are calculated. When determining the values for the optical quantities and the location and direction as well as the operating and ambient conditions, the measurement instants are also stored as “time stamps” and used for “synchronization” in the common evaluation.

The new measuring assembly also allows multidimensional influence parameters such as polarization, temporal modulation, angular and position dependence, including the retroaction of thermal and magnetic ambient conditions to be taken into consideration. Thus the measurement of photometric and colorimetric characteristics of displays can be traced back to the national standards which under international arrangements have been recognized as “equivalent”. Thus for medical, traffic and safety-relevant applications in particular, global marketing is ensured complying with strict regulations. The development aims to create new transfer standards which are made available to the users for improved production and quality control, for example, in the form of modified displays provided with stabilizing additional measures such as optical feedback and detailed measuring procedures.

Contact at PTB:

Phone: +49-531-592-0