The use of a light colour temperature of 4000 Kelvin in pedestrian underpasses is based on the results of tests of warm, neutral and cold white light from around 20 years ago.
The results then showed that neutral white light with 4000K achieved the highest customer satisfaction and lowest level of pollution. With the use of neutral white light in above-ground areas as well, up until now there has been homogeneous lighting across the whole station.
The decision to light above-ground areas with warm white light means we are losing this homogeneity. The effect of warm white light on customer satisfaction and pollution levels today will determine whether underground areas will be also be lit with 3000 Kelvin in future. We are carrying out tests to evaluate this.