A study of preferred illuminance and correlated colour temperature for LED office lighting

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 office lighting, a full-scale experiment was conducted in an office 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 office activities. The combination of 750 lx with 4000 K was statistically significantly preferred for office 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 office lighting and with the Asian and African groups the preference between 4000 and 5000 K depends upon illuminance levels.