Logadóttir, Ásta

Markvart, Jakob

Thorseth, Anders

Toftum, Jørn

At three different ambient temperatures, human subjects were exposed to correlated colour temperatures (CCT) in the range 2750 to 6230 K at an illuminance of 1000 lux. Significant associations were found between CCT and thermal sensation and between CCT and perceived stuffiness of the air

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Downloaded from orbit.dtu.dk on: Aug 03, 2018Occupant response to controllable LED lightingToftum, Jørn; Thorseth, Anders; Markvart, Jakob; Logadóttir, ÁstaPublication date:2018Document VersionPeer reviewed versionLink back to DTU OrbitCitation (APA):Toftum, J., Thorseth, A., Markvart, J., & Logadóttir, Á. (2018). Occupant response to controllable LED lighting.Paper presented at 15th Conference of the International Society of Indoor Air Quality and Climate, Philadelphia,United States.Occupant response to controllable LED lighting  Jørn Toftum1,*, Anders Thorseth1, Jakob Markvart2, Astá Lógadottir2  1 Technical University of Denmark, Copenhagen, Denmark 2 Danish Building Research Institute, Aalborg University, Copenhagen, Denmark *Corresponding email: jt@byg.dtu.dk  SUMMARY At three different ambient temperatures, human subjects were exposed to correlated colour temperatures (CCT) in the range 2750 to 6230 K at an illuminance of 1000 lux. Significant associations were found between CCT and thermal sensation and between CCT and perceived stuffiness of the air.  KEYWORDS  Correlated Colour Temperature, thermal sensation, perceived air quality, hue heat hypothesis.  1 INTRODUCTION LED technology that allows for control of illumination and colour temperature is currently introduced in many buildings, mostly due to its low energy use. In addition to energy efficien-cy, controllable LED lighting potentially may stimulate occupants’ perception of not only lighting, but also other aspects of the indoor environment, such as the thermal conditions or the air quality (e.g. Fanger et al. 1977, Winzen et al. 2014, Huebner et al. 2016). Even though findings in both older and newer literature are somewhat ambiguous, they generally seem to support the hypothesis that visual stimuli, in addition to parameters related with the body’s heat balance, may affect thermal perception. This indicates that controllable LED lighting may expand the temperature interval that building occupants find comfortable and thereby reduce the use of energy to heat and cool buildings. This study attempted to quantify associa-tions between CCT of LED lighting and thermal comfort and perceived air quality at tempera-tures on the upper and lower boundary of the summer and winter thermal comfort envelopes, respectively, and at a temperature optimal for winter comfort.  2 METHODS  Experiments were carried out with 44 human subjects (28 male and 16 female) seated in a controlled environment chamber. The lighting system in the chamber contained cold-white and warm-white diodes that could be dimmed separately to achieve CCTs in the range from 2746 K to 6231 K. Illuminance was kept constant at 1000 lux. At constant room temperature, the CCT was varied smoothly between plateaus at a rate that was imperceptible to the sub-jects. In balanced order, subjects were exposed to CCTs that varied from 2750 K to 6230 K and back to 2750 K or from 6230 K to 2750 K to 6230 K. Each exposure included five peri-ods lasting either 5 or 10 min at constant CCT during which questionnaires were completed. Experiments took place at three different operative temperatures at the lower boundary of the winter comfort envelope (19oC), at the winter comfort temperature (22oC), and at the upper boundary of the summer comfort envelope (27oC) (ISO 7730-2005). Clothing insulation cor-responded to standard summer (~0.5 clo) or winter (~1 clo) conditions.  During the experiments, CCT, operative temperature, relative humidity, and the CO2 concen-tration were measured, and subjects completed five identical questionnaires. The analysis fo-cused on two questions related with thermal sensation measured with a continuous 7-pt scale (ISO 7730-2005) and the perception of the air quality as measured with a categorical 5-pt scale ranging from Stuffy to Fresh. The association between CCT and thermal sensation was analysed in a mixed-effects model adjusted for time, clothing insulation, measured operative temperature, and with subject as random factor. The association between CCT and air stuffi-ness was analysed in a generalized estimating equation model (GEE) adjusted for CO2 con-centration and time. Both models used an exchangeable covariance structure to account for intra-subject correlation between questionnaires.  3 RESULTS AND DISCUSSION As expected, subjects’ mean thermal sensation approximated slightly cool at 19oC, neutral at 22oC and slightly warm at 27oC (Figure 1a). The air was perceived as being more stuffy at 27oC than at 22oC or 19oC (Figure 1b), despite comparable CO2 levels in the chamber air.  ColdCoolSl. coolNeutralSl. warmWarmHotThermal sensation2000 3000 4000 5000 6000 7000Colour temperature [K]19oC 22oC 27oC StuffySl. stuffyNeither freshor stuffySl. freshFreshPerceived air quality2000 3000 4000 5000 6000 7000Colour temperature [K]19oC 22oC 27oC Figure 1. Association between the mean thermal sensation and the CCT (a-left) and between the mean perceived air stuffiness and CCT (b-right). Error bars indicate standard deviations.  The initial hypothesis was that the effect of CCT on subjective perceptions would be most pronounced on the boundaries of the comfort zone (19oC and 27oC), but at these temperatures the responses were not associated with the CCT. Therefore, the following summarizes only results of the statistical analyses of experiments at 22oC. When adjusting for covariates and random subject effects, the association between CCT and thermal sensation was significant with an effect estimate of -0.000992 (scale units)/(K CCT) (p < 0.01; mixed effects model). This corresponds to a difference in mean thermal sensation of 0.35 scale units at the differ-ence between the minimum and maximum CCT applied. Likewise, the air stuffiness improved 0.4 scale units in the same CCT range (p < 0.01; GEE).   These findings were achieved under well-controlled conditions in a test chamber without in-terference from daylight or light from computer monitors that will be present in most office environments. Next step is therefore to repeat the study in a real-world setting to evaluate if CCT, also in practice, can modulate thermal comfort and other subjective responses.  4 ACKNOWLEDGEMENT This study was supported financially by the ELFORSK research programme, project 348-030.   5 REFERENCES  Fanger, PO., Breum, NO., Jerking, E. 1977. Ergonomics, 20(1), 11-18. Hübner, GM, Shipworth, DT, Gauthier, S, Witzel, C, Raynham, P & Chan, W. 2016. Energy Research and Social Science, 15, 45-57. ISO 7730 2005. International Organization for Standardization, Geneva. Winzen, J., Albers, F., & Marggraf-Micheel, C. 2014. Lighting Research and Technology, 46(4), 465–475. 

Occupant response to controllable LED lighting

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Occupant response to controllable LED lighting

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