Dissertation in the field of Illumination Engineering, Rajendra Dangol

The title of thesis is Subjective preference of light colour and LED lighting

Light emitting diode (LED) based lighting technology has huge potential to save energy and provides enormous opportunities to adjust the lighting according to actual needs. However, the user preference of LED lighting is not well known and colour quality of LED lighting is a big concern. This thesis examined experimentally different spectral power distribution (SPD) of LED light sources with the help of user acceptance studies in several viewing condition. The work was started with a study implemented on a lighting booth with 21 LED SPD optimized with the help of different colour quality metrics. Sixty observers evaluated the different LED SPDs individually and by comparison with fluorescent lamps at respective correlated colour temperature (CCT) by answering questionnaire. The study showed that the CIE colour rendering index does not explain observer’s preferences, whereas the   reference based metrics and area or volume based metrics, together, explained better observer’s subjective assessments. These results were again examined in real size office rooms with help of 40 observers, and the results were similar. Another aspect approached was demonstration that simplified LED, having three peaks, can have similar colour quality properties regarding preference as more complex LED SPD (with many peaks). The results from real office room experiment also showed that the observer preferred CCT of 4000 K and illuminance level of 500 lux for office lighting. Finally, the experiment conducted to test the performance of different fidelity metrics showed that the colour quality scale provides best prediction for Led light sources that enhance the object chroma.

The results presented in this thesis helps to understand the subjective preferences regarding the colour quality of LED lighting and to select the suitable metrics that well define the subjective preference. These results not only help the light source manufactures but also help end-users to select appropriate LED light sources. 

Opponent: Associate Professor Thorbjörn Laike, Lund University, Sweden

Supervisor: Professor Liisa Halonen Aalto University School of Electrical Engineering, Department of Electrical Engineering and Automation

Dissertation website

Contact information:
Rajendra Dangol
tel. +358 50 3161 005
rajendra.dangol@aalto.fi