Executive Summary

Two psycho-physiological studies were performed on large area emitters simulating the use of OLEDs in an office environment with a computer work place for the test persons.

A contrast sensitivity test was performed with the test persons requiring fast recognition and reaction and they had to answer questions on light quality and their perceived work load. In parallel, physiological data such as heart rate variations, blink frequency and skin conductance were recorded.

In the first study two scenarios were compared focusing on light reflecting walls on one hand and self luminous wall surfaces on the other hand. In both scenarios the luminance / illuminance levels of the ambiencet were varied as well as the luminance of the monitor screen where the subjects had to test their visual performance.

Only the light quality of both test conditions was evaluated differently. Self-luminous surfaces with high luminances (660 cd/m²) were perceived more pleasant and in the case of lower luminance (40 cd/m² and also 130 cd/m²) more tiring and monotonous than light reflecting vertical surfaces. No other significant differences between reflecting and self luminous surfaces could be found. Differences could be only detected by comparing different monitor brightness levels with each other or different ambient illuminance levels with each other.

In the second study two different light intensity distributions were simulated. A ceiling illumination with Lambertian emission characteristics was realized and compared with a classical glare-free set-up providing a more pronounced illumination on the working surface and the lower area of walls. Substantially different results with regard to their visual performance and perceived light quality were achieved.

A significantly lower visual performance was measured with a diffuse radiating ceiling illumination system (i.e. Lambertian characteristics). Furthermore, this system proved to be more tiring, monotonous and demotivating at higher luminance levels (i.e. 890 cd/m²). No significant differences in the physiological reactions of the test persons between the test conditions were revealed.

This is mainly due to the fact that the study design and the applied visual performance test had more impact to the physiological reactions than the different lighting conditions tested in study 2. Basically, this is also valid for study 1.

The major conclusions drawn from these results are:

• Self luminous surfaces do not really differ from reflecting surfaces with regard to physiological impact. At luminance levels from 600 to 1000 cd/m² (representing the OLED100.eu working level) they are even perceived as more pleasant. This opens opportunities for direct view and vertical applications (wall tiles).
• For large area ceiling applications, especially in working environment, OLEDs should provide a different light intensity distribution. Though the Lambertian profile does not violate glare norms and required horizontal illuminance levels can be easily achieved with OLEDs, the light quality of such a scenario is ranked worse and this has obviously impact on performance skills. This is a very important input to OLED R&D for the definition of future products and requires some readjustment for light extraction work.