Light & Engineering Vol. 23, No. 3, pp. 39-47, 2015 Svetotekhnika No. 4, 2015, pp. 53-58 A STUDY OF PREFERRED ILLUMINANCE AND CORRELATED COLOUR TEMPERATURE FOR LED OFFICE LIGHTING Rupak Raj Baniya, Eino Tetri, and Liisa Halonen Lighting Unit, School of Electrical Engineering, Aalto University, Espoo, Finland Email: rupak.baniya@aalto.fi ABSTRACT In order to study the preferred combination of the illuminance level and correlated colour temperature (CCT) and the preferred CCT of different ethnic groups in offi ce lighting, a full-scale experiment was conducted in an offi ce room with a light-emitting diode (LED) luminaires. <...> Fifty-three observers from three different ethnic groups (Asian, European and African) rated nine different preset lighting situations after performing different offi ce activities. <...> The combination of 750 lx with 4000 K was statistically signifi cantly preferred for offi ce lighting. <...> It was also found that the impression of brightness increases with a higher CCT and that people feel more stimulated under a higher CCT compared to a lower CCT. <...> The European group preferred a lit environment under CCT 4000 K for offi ce lighting and with the Asian and African groups the preference between 4000 and 5000 K depends upon illuminance levels. <...> Keywords: illuminance level, correlated colour temperature, LED lighting, offi ce lighting 1. <...> INTRODUCTION Lighting preference is related to variety of human reactions to lighting, such as comfort, aesthetics and performance [1]. <...> Illuminance (E) and correlated colour temperature (CCT) are two important characteristics of light to be considered with regard 39 to human perception [5]. <...> There is a quantitatively recommended illuminance value for indoor spaces but no equivalent recommendation for CCT. <...> The European standard [6] for offi ce lighting recommends an illuminance value of 500 lx for general offi ces. <...> Some studies [7–9] reported a preference for an illuminance level higher than the recommended, while other studies [10–12] showed a preference for lower illuminance than the recommended level for offi ce lighting. <...> Studies about the effect of CCT on different aspects of lighting suggest that the CCT has an effect on the visual impression of a lit space, on physiological responses and on subjective mood [2,13 <...>