Dissertation in the field of Illumination Engineering, Mohammad Shahidul Islam

The title of thesis is User acceptance studies for LED office lighting: light spectrum and correlated colour temperature

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. The measurement techniques developed for the conventional light sources to measure quality and characteristics of light are not always suitable for LEDs. The colour rendering properties and the correlated colour temperature (CCT) are important aspects for user acceptability of a light source. However, the CIE colour rendering index (CRI) is not well-suited for white LED light. It is also not well-known how end-users would evaluate the LED lighting in offices. This thesis work considers end-users' evaluation of LED lighting in office environment and thus explores the end-users' preferences and acceptance of a lit environment under different types of LED spectra. For this purpose, two experiments were carried out with different LED light spectra and CCTs. The LED spectra were realised considering colour quality scale (CQS) gamut area scale Qg, CQS Colour preference scale Qp, feeling of contrast index (FCI) along with CIE CRI at 2700K, 4000K and 6500K.

The CCT 4000K was preferred to 2700K and 6500K for office lighting at illumi-nance of 500 lux. At 4000K, the observers preferred the LED light spectra which had higher values of a reference based metric (Qp) and higher values of an area-based metric (Qg or GAI) to the fluorescent lamps in the office environment at 500 lux. The findings of the study indicated that it is possible to develop LED SPDs that can be preferred and accepted by end-users and thus LED lighting can be a viable option in office environments. It would be a good option to realise LED light sources with small number of LED types while maintaining the criteria of good lighting in the office environment. The results indicated the need to develop LED light spectra for office lighting considering Qp and Qg with negative Duv values within the recommended limit. The colour of white light should be characterised not only by CCT but also by Duv values.

Opponent: Professor Tran Quoc Khanh, Technical University of Darmstadt, Germany

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

Electronic dissertation thesis (aaltolib.aalto.fi)

More information:

Mohammad Shahidul Islam
tel. +358 44 3435 435
mohammad.islam@aalto.fi