The ‘hue-heat’ hypothesis states that an environment which has wavelengths predominantly toward the red end of the visual spectrum feels ‘warm’ and one with wavelengths mainly toward the blue end feels ‘cool’. In order to test the hypothesis and to study the impacts of the correlated colour temperature of a light source on thermal sensation and thermal comfort, a study was conducted in a test room illuminated with an Light Emitting Diode (LED) lighting system with an adjustable correlated colour temperature where air temperature, air velocity, and relative humidity were kept constant. The correlated colour temperature of lighting inside the test room was changed gradually while keeping the colour rendering index values greater than 90, an illuminance level of 500 lx, and chromaticity difference (Duv) values within the limits of ±0.005. Sixteen study subjects were exposed to a ‘high room temperature’ (25℃) and a ‘low room temperature’ (20℃) on different days. The subjects were adapted to low correlated colour temperature (2700 K), medium correlated colour temperature (4000 K), and high correlated colour temperature (6200 K) lighting for 10 min and subsequently completed the questionnaire about their thermal comfort and thermal sensation. The results of this survey did not provide support for the hue-heat hypothesis and indicated that people felt thermally more comfortable in an indoor workplace at the correlated colour temperature of 4000 K than at the correlated colour temperature of 2700 K or 6200 K.
Abstract-This paper investigates the correlation between color quality and energy efficiency of indoor lighting control. The color quality, in terms of visual performance and comfort, is quantified using three measurements: illuminance, Color Rendering Index, and Correlated Color Temperature. Several experiments have been conducted to evaluate the potential energy savings of using different portions of light spectrum to obtain the optimal color quality. In particular, Light-Emitting Diodes are used as the lighting sources of the experimental luminaire. Moreover, the above quantification method and experimental results have been incorporated into a previously developed simulation framework for Building Automation and Control Systems, and smart lighting is used to adjust the tradeoff between comfort and energy consumption based on the presence of occupants. The results can be used to evaluate the viability of advanced lighting automation.
In previous user-acceptance studies conducted at Aalto University, it was found that the preferred light-emitting diode spectral power distributions (SPDs) were not characterised by a high-CIE colour-rendering index but by a high-colour quality index (CQS) colour preference scale (Qp) and a high-CQS gamut area scale (Qg). In these studies, the SPDs were realised with a 12-channel LED spectra simulator. It is, however, foreseen that LED light sources consisting of 12 different types of LEDs will not be commercially exploitable due to complexity. The objective of this work was to investigate the possibility of generating simplified LED SPDs having CQS Qp and CQS Qg values similar to those of the preferred complex LED SPDs found in the previous user-acceptance studies. Useracceptance studies were carried out in lighting booths to investigate people's preferences for the lit environment under both the complex and simplified LED spectra. The results suggest that the preferred complex LED SPDs can be optimized both for efficiency and cost without sacrificing the colour quality of the light.
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