User acceptance studies for LED office lighting: light spectrum and correlated colour temperature

Mohammad Shahidul Islam

Research output: ThesisDoctoral ThesisCollection of Articles

Abstract

During the last decade, lighting technology based on light-emitting diodes (LEDs) has advanced rapidly and is paving the way for the application of LED lighting in offices. Two experiments were carried out to study user preference for different LED light spectra and correlated colour temperature (CCT), and to determine user acceptance for LED office lighting. In a lighting booth experiment, twenty one different LED spectral power distributions (SPDs) were realised considering colour quality scale (CQS) gamut area scale Qg, CQS Colour preference scale Qp, feeling of contrast index (FCI) along with the CIE colour rendering index (CRI) at the CCTs of 2700K, 4000K, and 6500K. The observers evaluated the lit scenes under different light spectra at 500 lux for different factors such as brightness, visual comfort, and pleasantness. The observers preferred the LED SPDs which had higher values of a reference-based metric (Qp) or higher values of an area-based metric (Qg). The chromaticity difference (Duv) values also influenced the user preference of the light spectra. The observer preferred the CCT of 4000K and 6500K to the CCT of 2700K at 500 lux. The findings of the lighting booth experiment were used as the base line for the office room experiment where six different LED SPDs were realised at the CCTs of 4000K and 6500K considering Qp, Qg, and FCI. The observers evaluated the lit environments under different SPDs for brightness, visual comfort, glare, and pleasantness of colour of light along with other lighting aspects at illuminance levels of 300 lux and 500 lux. At 4000K, the observers preferred the LED light spectra which had higher values of Qp and Qg to the fluorescent lamps in the office environment at 500 lux. The preferred LED SPDs had negative Duv values, whereas the fluorescent lamp had positive Duv values. The observers preferred the CCT of 4000K to 6500K, under which the observers felt more comfortable and found the colour of light more pleasant than under 6500K at 500 lux. It was also found that the lit environment should be able to provide good quality lighting for visibility and the observers should feel visually comfortable in that lit environment if the illuminance level is varied. The results indicate the need to develop LED light spectra for office lighting considering Qp and Qg with negative Duv values within the recommended limit. As the Duv values affected the observers' preferences, colour of white light should be characterised not only by CCT but also by Duv values.
Translated title of the contributionUser acceptance studies for LED office lighting: light spectrum and correlated colour temperature
Original languageEnglish
QualificationDoctor's degree
Awarding Institution
  • Aalto University
Supervisors/Advisors
  • Halonen, Liisa, Supervisor
  • Bhusal, Pramod, Advisor
Publisher
Print ISBNs978-952-60-6119-1
Electronic ISBNs978-952-60-6120-7
Publication statusPublished - 2015
MoE publication typeG5 Doctoral dissertation (article)

Keywords

  • light emitting diode
  • spectra
  • office lighting
  • colour rendering
  • correlated colour temperature
  • preference
  • acceptance

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