Subjective preference of light colour and LED lighting

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School of Electrical Engineering | Doctoral thesis (article-based) | Defence date: 2015-05-15
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Authors

Date

2015

Department

Sähkötekniikan ja automaation laitos
Department of Electrical Engineering and Automation

Major/Subject

Mcode

Degree programme

Language

en

Pages

58 + app. 132

Series

Aalto University publication series DOCTORAL DISSERTATIONS, 56/2015

Abstract

The main objective of this work is to investigate the subjective preferences for lighting environments under different LED spectral power distributions (SPDs) and to analyse the different existing colour quality descriptors in order to recommend the best descriptor. An additional aim of the work is to find out the correlated colour temperature (CCT) and illuminance levels that users prefer for LED lighting. The experiments were conducted in lighting booths and in office rooms, where the subjective preferences for different LED light spectra were studied. In the lighting booth experiments, seven different LED SPDs were studied at CCTs of 2700 K, 4000 K and 6500 K at 500 lux. The study showed that the observers preferred the LED SPDs which increased the object chroma and colourfulness values (calculated in CIECAM02-UCS). Also, the preferred LED SPDs had higher values of reference-based metrics (such as colour quality scale (CQS) colour preference scale) and higher values of area-based metrics (such as CQS colour gamut scale or gamut area index (GAI)). The observers preferred the light sources at CCT of 4000 K and 6500 K over the CCT of 2700 K. The work was continued by simulation work and user acceptance studies to find out the simplified LED SPDs that the observers would prefer. The simulation results suggested that it is possible to generate simplified LED SPDs that have CQS Qp and CQS Qg values similar to those of the preferred complex SPDs that were generated by 9 to 11 different types of LEDs. The user acceptance studies conducted in the lighting booths also showed that the simplified LED SPDs using three different types of LEDs were preferred over complex LED SPD. Later, similar simplified LED SPDs were also studied in office rooms, and it was found that the observers preferred simplified LED SPDs over fluorescent lamp. The three different LED SPDs at each CCT of 4000 K and 6500 K were studied in the office room experiments. The observers preferred most the LED SPDs with high CQS Qp and CQS Qg or GAI values and least the LED SPDs that had the lowest CQS Qp and CQS Qg values. Also, the light sources (having high CQS Qp and CQS Qg) with negative Duv values were more preferred over light sources with positive Duv values maintaining the Duv values within the limit of ±0.0054. Moreover, for the office lighting, the observers preferred CCT of 4000 K over CCT of 6500 K at 500 lux. It was also found that the observers preferred the illuminance level of 500 lux over 300 lux. The results of the experiments conducted in the lighting booths to test the performance of different fidelity metrics showed that the CIE CRI, CRI2012 and CQS provide similar predictions for LED light sources that do not enhance the object chroma. It was found that the best prediction of colour fidelity was provided by CQS for LED light sources that enhance object chroma.

Description

Supervising professor

Halonen, Liisa, Prof., Aalto University, Department of Electrical Engineering and Automation, Finland

Thesis advisor

Bhusal, Pramod, Dr., Aalto University, Department of Electrical Engineering and Automation, Finland

Keywords

light emitting diode, preference, naturalness, colourfulness, colour rendering, colour quality, colour fidelity, office lighting

Other note

Parts

  • [Publication 1]: Dangol, R; Islam, M; Hyvärinen, M; Bhusal, P; Puolakka, M; Halonen, L. 2013. Subjective preferences and colour quality metrics of LED light sources. Lighting Research and Technology, volume 45, number 6, pages 666-688.
    DOI: 10.1177/1477153512471520 View at publisher
  • [Publication 2]: Islam, M; Dangol, R; Hyvärinen, M; Bhusal, P; Puolakka, M; Halonen, L. 2013. User preferences for LED lighting in terms of light spectrum. Lighting Research and Technology, volume 45, number 6, pages 641-665.
    DOI: 10.1177/1477153513475913 View at publisher
  • [Publication 3]: Baniya, R.R; Dangol, R; Bhusal, P; Wilm, A; Baur, E ; Puolakka, M; Halonen, L. 2015. User-acceptance studies for simplified light-emitting diode spectra. Lighting Research and Technology, volume 47, number 2, pages 177-191.
    DOI: 10.1177/1477153513515264 View at publisher
  • [Publication 4]: Dangol, R; Islam, M; Hyvärinen, M; Bhusal, P; Puolakka, M; Halonen, L. 2015. User acceptance studies for LED office lighting: Preference, naturalness and colourfulness. Lighting Research and Technology, volume 47, number 1, pages 36-53.
    DOI: 10.1177/1477153513514424 View at publisher
  • [Publication 5]: Islam, M; Dangol, R; Hyvärinen, M; Bhusal, P; Puolakka, M; Halonen, L. 2015. User acceptance studies for LED office lighting: lamp spectrum, spatial brightness and illuminance level. Lighting Research and Technology, volume 47, number 1, pages 54-79.
    DOI: 10.1177/1477153513514425 View at publisher
  • [Publication 6]: Dangol, R; Bhusal, P; Halonen L. 2014. Performance of colour fidelity metrics. Lighting Research and Technology, first published online on October 22, 2014 as
    DOI: 10.1177/1477153514555721 View at publisher

Citation

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https://urn.fi/URN:ISBN:978-952-60-6180-1

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[diss] Sähkötekniikan korkeakoulu / ELEC