The Experts below are selected from a list of 34839 Experts worldwide ranked by ideXlab platform

Luc J M Schlangen - One of the best experts on this subject based on the ideXlab platform.

  • Correlated Colour Temperature of morning light influences alertness and body Temperature
    Physiology & behavior, 2017
    Co-Authors: Marije Te Kulve, Luc J M Schlangen, L Lisje Schellen, Jl Souman, Wouter D. Van Marken Lichtenbelt
    Abstract:

    Though several studies have reported human alertness to be affected by the intensity and spectral composition of ambient light, the mechanism behind this effect is still largely unclear, especially for daytime exposure. Alerting effects of nocturnal light exposure are correlated with melatonin suppression, but melatonin levels are generally low during the day. The aim of this study was to explore the alerting effect of light in the morning for different correlated Colour Temperature (CCT) values, as well as its interaction with ambient Temperature. Body Temperature and perceived comfort were included in the study as possible mediating factors. In a randomized crossover design, 16 healthy females participated in two sessions, once under 2700K and once under 6500K light (both 55lx). Each session consisted of a baseline, a cool, a neutral and a warm thermal environment. Alertness as measured in a reaction time task was lower for the 6500K exposure, while subjective sleepiness was not affected by CCT. Also, core body Temperature was higher under 6500K. Skin Temperature parameters and perceived comfort were positively correlated with subjective sleepiness. Reaction time correlated with heat loss, but this association did not explain why the reaction time was improved for 2700K.

  • The effect of high correlated Colour Temperature office lighting on employee wellbeing and work performance
    Journal of circadian rhythms, 2007
    Co-Authors: Peter R Mills, Susannah C Tomkins, Luc J M Schlangen
    Abstract:

    The effects of lighting on the human circadian system are well-established. The recent discovery of 'non-visual' retinal receptors has confirmed an anatomical basis for the non-image forming, biological effects of light and has stimulated interest in the use of light to enhance wellbeing in the corporate setting. A prospective controlled intervention study was conducted within a shift-working call centre to investigate the effect of newly developed fluorescent light sources with a high correlated Colour Temperature (17000 K) upon the wellbeing, functioning and work performance of employees. Five items of the SF-36 questionnaire and a modification of the Columbia Jet Lag scale, were used to evaluate employees on two different floors of the call centre between February and May 2005. Questionnaire completion occurred at baseline and after a three month intervention period, during which time one floor was exposed to new high correlated Colour Temperature lighting and the other remained exposed to usual office lighting. Two sided t-tests with Bonferroni correction for type I errors were used to compare the characteristics of the two groups at baseline and to evaluate changes in the intervention and control groups over the period of the study. Individuals in the intervention arm of the study showed a significant improvement in self-reported ability to concentrate at study end as compared to those within the control arm (p < 0.05). The mean individual score on a 5 point Likert scale improved by 36.8% in the intervention group, compared with only 1.7% in the control group. The majority of this improvement occurred within the first 7 weeks of the 14 week study. Substantial within group improvements were observed in the intervention group in the areas of fatigue (26.9%), alertness (28.2%), daytime sleepiness (31%) and work performance (19.4%), as assessed by the modified Columbia Scale, and in the areas of vitality (28.4%) and mental health (13.9%), as assessed by the SF-36 over the study period. High correlated Colour Temperature fluorescent lights could provide a useful intervention to improve wellbeing and productivity in the corporate setting, although further work is necessary in quantifying the magnitude of likely benefits.

  • The effect of high correlated Colour Temperature office lighting on employee wellbeing and work performance.
    Journal of circadian rhythms, 2007
    Co-Authors: Peter R Mills, Susannah C Tomkins, Luc J M Schlangen
    Abstract:

    BACKGROUND The effects of lighting on the human circadian system are well-established. The recent discovery of 'non-visual' retinal receptors has confirmed an anatomical basis for the non-image forming, biological effects of light and has stimulated interest in the use of light to enhance wellbeing in the corporate setting. METHODS A prospective controlled intervention study was conducted within a shift-working call centre to investigate the effect of newly developed fluorescent light sources with a high correlated Colour Temperature (17000 K) upon the wellbeing, functioning and work performance of employees. Five items of the SF-36 questionnaire and a modification of the Columbia Jet Lag scale, were used to evaluate employees on two different floors of the call centre between February and May 2005. Questionnaire completion occurred at baseline and after a three month intervention period, during which time one floor was exposed to new high correlated Colour Temperature lighting and the other remained exposed to usual office lighting. Two sided t-tests with Bonferroni correction for type I errors were used to compare the characteristics of the two groups at baseline and to evaluate changes in the intervention and control groups over the period of the study. RESULTS Individuals in the intervention arm of the study showed a significant improvement in self-reported ability to concentrate at study end as compared to those within the control arm (p < 0.05). The mean individual score on a 5 point Likert scale improved by 36.8% in the intervention group, compared with only 1.7% in the control group. The majority of this improvement occurred within the first 7 weeks of the 14 week study. Substantial within group improvements were observed in the intervention group in the areas of fatigue (26.9%), alertness (28.2%), daytime sleepiness (31%) and work performance (19.4%), as assessed by the modified Columbia Scale, and in the areas of vitality (28.4%) and mental health (13.9%), as assessed by the SF-36 over the study period. CONCLUSION High correlated Colour Temperature fluorescent lights could provide a useful intervention to improve wellbeing and productivity in the corporate setting, although further work is necessary in quantifying the magnitude of likely benefits.

J L Gardner - One of the best experts on this subject based on the ideXlab platform.

  • Uncertainties in source distribution Temperature and correlated Colour Temperature
    Metrologia, 2006
    Co-Authors: J L Gardner
    Abstract:

    Uncertainties in the distribution Temperature (DT) and correlated Colour Temperature are estimated for common sources and typical measurement uncertainties of a spectral transfer from a reference lamp. Uncertainty sensitivity coefficients for both parameters in terms of measured values of spectral irradiance are derived using a generalized matrix inverse. The uncertainty values are compared with differences in the source Temperature parameters. DT is calculated using the CIE definition; shifts in DT due to the alternative of a direct fit of Planck's distribution, and to including weights in the process, are compared with the estimated uncertainties.

  • Correlated Colour Temperature - uncertainty and estimation
    Metrologia, 2000
    Co-Authors: J L Gardner
    Abstract:

    Correlated Colour Temperature (CCT) of a source is estimated from position in CIE 1960 (u, v) Colour space in relation to the black-body locus. In this paper, the methods of the ISO Guide to the Expression of Uncertainty in Measurement are applied to derive analytical expressions for uncertainty in u and v chromacity coordinates and CCT, including correlation effects. Uncertainty in CCT is found by fitting the form of the black-body locus and relevant derivatives. Examples are given for calibration of four typical sources of spectral distributions. Accurate CCT is determined by a search technique. An alternative method using fitted functions to solve for CCT using the geometry in (u, v) space is presented. An uncertainty in CCT of a few kelvin can be achieved.

W. Chan - One of the best experts on this subject based on the ideXlab platform.

  • Saving energy with light? Experimental studies assessing the impact of Colour Temperature on thermal comfort
    Energy Research & Social Science, 2016
    Co-Authors: Gesche M. Huebner, David Shipworth, Stephanie Gauthier, Christoph Witzel, P. Raynham, W. Chan
    Abstract:

    We tested whether the Colour Temperature of the illumination (realised through manipulating the ceiling light) impacted on thermal comfort, based on the hypothesis that a lower Colour Temperature is associated with feeling warmer and a higher Colour Temperature with feeling cooler. If confirmed, then light might be a tool for energy-saving through allowing ambient air Temperatures to vary over a wider range and hence reducing the need for space heating and cooling. Testing took place in a climate chamber. In Study 1, comfort ratings were collected using thermal comfort surveys (N = 32). In Study 2, an observational design was used, where changes in clothing level, interpreted as thermal discomfort responses, were observed (N = 32). We compared comfort ratings and changes in clothing level under light with a Colour Temperature of 2700 K vs. 6500 K. Results partly confirmed the hypotheses: both self-report and observation indicated higher comfort under the low Colour Temperature. Further research will need to replicate findings in a real-world setting to see if light might indeed be a tool to modulate thermal comfort, and hence reduce usage of heating and cooling.

Peter R Mills - One of the best experts on this subject based on the ideXlab platform.

  • The effect of high correlated Colour Temperature office lighting on employee wellbeing and work performance
    Journal of circadian rhythms, 2007
    Co-Authors: Peter R Mills, Susannah C Tomkins, Luc J M Schlangen
    Abstract:

    The effects of lighting on the human circadian system are well-established. The recent discovery of 'non-visual' retinal receptors has confirmed an anatomical basis for the non-image forming, biological effects of light and has stimulated interest in the use of light to enhance wellbeing in the corporate setting. A prospective controlled intervention study was conducted within a shift-working call centre to investigate the effect of newly developed fluorescent light sources with a high correlated Colour Temperature (17000 K) upon the wellbeing, functioning and work performance of employees. Five items of the SF-36 questionnaire and a modification of the Columbia Jet Lag scale, were used to evaluate employees on two different floors of the call centre between February and May 2005. Questionnaire completion occurred at baseline and after a three month intervention period, during which time one floor was exposed to new high correlated Colour Temperature lighting and the other remained exposed to usual office lighting. Two sided t-tests with Bonferroni correction for type I errors were used to compare the characteristics of the two groups at baseline and to evaluate changes in the intervention and control groups over the period of the study. Individuals in the intervention arm of the study showed a significant improvement in self-reported ability to concentrate at study end as compared to those within the control arm (p < 0.05). The mean individual score on a 5 point Likert scale improved by 36.8% in the intervention group, compared with only 1.7% in the control group. The majority of this improvement occurred within the first 7 weeks of the 14 week study. Substantial within group improvements were observed in the intervention group in the areas of fatigue (26.9%), alertness (28.2%), daytime sleepiness (31%) and work performance (19.4%), as assessed by the modified Columbia Scale, and in the areas of vitality (28.4%) and mental health (13.9%), as assessed by the SF-36 over the study period. High correlated Colour Temperature fluorescent lights could provide a useful intervention to improve wellbeing and productivity in the corporate setting, although further work is necessary in quantifying the magnitude of likely benefits.

  • The effect of high correlated Colour Temperature office lighting on employee wellbeing and work performance.
    Journal of circadian rhythms, 2007
    Co-Authors: Peter R Mills, Susannah C Tomkins, Luc J M Schlangen
    Abstract:

    BACKGROUND The effects of lighting on the human circadian system are well-established. The recent discovery of 'non-visual' retinal receptors has confirmed an anatomical basis for the non-image forming, biological effects of light and has stimulated interest in the use of light to enhance wellbeing in the corporate setting. METHODS A prospective controlled intervention study was conducted within a shift-working call centre to investigate the effect of newly developed fluorescent light sources with a high correlated Colour Temperature (17000 K) upon the wellbeing, functioning and work performance of employees. Five items of the SF-36 questionnaire and a modification of the Columbia Jet Lag scale, were used to evaluate employees on two different floors of the call centre between February and May 2005. Questionnaire completion occurred at baseline and after a three month intervention period, during which time one floor was exposed to new high correlated Colour Temperature lighting and the other remained exposed to usual office lighting. Two sided t-tests with Bonferroni correction for type I errors were used to compare the characteristics of the two groups at baseline and to evaluate changes in the intervention and control groups over the period of the study. RESULTS Individuals in the intervention arm of the study showed a significant improvement in self-reported ability to concentrate at study end as compared to those within the control arm (p < 0.05). The mean individual score on a 5 point Likert scale improved by 36.8% in the intervention group, compared with only 1.7% in the control group. The majority of this improvement occurred within the first 7 weeks of the 14 week study. Substantial within group improvements were observed in the intervention group in the areas of fatigue (26.9%), alertness (28.2%), daytime sleepiness (31%) and work performance (19.4%), as assessed by the modified Columbia Scale, and in the areas of vitality (28.4%) and mental health (13.9%), as assessed by the SF-36 over the study period. CONCLUSION High correlated Colour Temperature fluorescent lights could provide a useful intervention to improve wellbeing and productivity in the corporate setting, although further work is necessary in quantifying the magnitude of likely benefits.

M. Juvela - One of the best experts on this subject based on the ideXlab platform.

  • The degeneracy between dust Colour Temperature and spectral index
    Astronomy and Astrophysics - A&A, 2013
    Co-Authors: M. Juvela, N. Ysard, J. Montillaud, T. Lunttila
    Abstract:

    Context. Submillimetre dust emission provides information on the physics of interstellar clouds and dust. However, noise can produce a spurious anticorrelation between the Colour Temperature TC and the spectral index β. These artefacts must be separated from the intrinsic β(T) relation of dust emission. Aims: We compare methods that can be used to analyse the β(T) relation. We wish to quantify their accuracy and bias, especially for observations similar to those made with Planck and Herschel. Methods: We examine submillimetre observations that are simulated either as simple, modified black body emission or using 3D radiative transfer modelling. We used different methods to recover the (T, β) values of individual objects and the parameters of the β(T) relation. In addition to χ2 fitting, we examined the results of the SIMEX method, basic Bayesian model, hierarchical models, and a method that explicitly assumes a functional form for β(T). The methods were also applied to one field observed by Herschel. Results: All methods exhibit some bias, even in the idealised case of white noise. The results of the Bayesian method show significantly lower bias than direct χ2 fits. The same is true for hierarchical models that also result in a smaller scatter in the Temperature and spectral index values. However, significant bias was observed in cases with high noise levels. When the signal-to-noise ratios are different for different sources, all β and T estimates of the hierarchical model are biased towards the relation determined by the data with the highest signal-to-noise ratio. This can significantly alter the recovered β(T) function. With the method where we explicitly assume a functional form for the β(T) relation, the bias is similar to the Bayesian method. In the case of the actual Herschel field, all methods agree on some degree of anticorrelation between T and β. Conclusions: The Bayesian method and the hierarchical models can both reduce the noise-induced parameter correlations. However, all methods can exhibit non-negligible bias. This is particularly true for hierarchical models and observations of varying signal-to-noise ratios and this must be taken into account when interpreting the results.

  • The degeneracy between dust Colour Temperature and spectral index - Comparison of methods for estimating the β(T) relation
    Astronomy & Astrophysics, 2013
    Co-Authors: M. Juvela, N. Ysard, J. Montillaud, T. Lunttila
    Abstract:

    Sub-millimetre dust emission provides information on the physics of interstellar clouds and dust. Noise can produce anticorrelation between the Colour Temperature T_C and the spectral index beta. This must be separated from the intrinsic beta(T) relation of dust. We compare methods for the analysis of the beta(T) relation. We examine sub-millimetre observations simulated as simple modified black body emission or using 3D radiative transfer modelling. In addition to chi^2 fitting, we examine the results of the SIMEX method, basic Bayesian model, hierarchical models, and one method that explicitly assumes a functional form for beta(T). All methods exhibit some bias. Bayesian method shows significantly lower bias than direct chi^2 fits. The same is true for hierarchical models that also result in a smaller scatter in the Temperature and spectral index values. However, significant bias was observed in cases with high noise levels. Beta and T estimates of the hierarchical model are biased towards the relation determined by the data with the highest S/N ratio. This can alter the recovered beta(T) function. With the method where we explicitly assume a functional form for the beta(T) relation, the bias is similar to the Bayesian method. In the case of an actual Herschel field, all methods agree, showing some degree of anticorrelation between T and beta. The Bayesian method and the hierarchical models can both reduce the noise-induced parameter correlations. However, all methods can exhibit non-negligible bias. This is particularly true for hierarchical models and observations of varying signal-to-noise ratios and must be taken into account when interpreting the results.

  • the degeneracy between dust Colour Temperature and spectral index comparison of methods for estimating the beta t relation
    arXiv: Astrophysics of Galaxies, 2013
    Co-Authors: M. Juvela, N. Ysard, J. Montillaud, T. Lunttila
    Abstract:

    Sub-millimetre dust emission provides information on the physics of interstellar clouds and dust. Noise can produce anticorrelation between the Colour Temperature T_C and the spectral index beta. This must be separated from the intrinsic beta(T) relation of dust. We compare methods for the analysis of the beta(T) relation. We examine sub-millimetre observations simulated as simple modified black body emission or using 3D radiative transfer modelling. In addition to chi^2 fitting, we examine the results of the SIMEX method, basic Bayesian model, hierarchical models, and one method that explicitly assumes a functional form for beta(T). All methods exhibit some bias. Bayesian method shows significantly lower bias than direct chi^2 fits. The same is true for hierarchical models that also result in a smaller scatter in the Temperature and spectral index values. However, significant bias was observed in cases with high noise levels. Beta and T estimates of the hierarchical model are biased towards the relation determined by the data with the highest S/N ratio. This can alter the recovered beta(T) function. With the method where we explicitly assume a functional form for the beta(T) relation, the bias is similar to the Bayesian method. In the case of an actual Herschel field, all methods agree, showing some degree of anticorrelation between T and beta. The Bayesian method and the hierarchical models can both reduce the noise-induced parameter correlations. However, all methods can exhibit non-negligible bias. This is particularly true for hierarchical models and observations of varying signal-to-noise ratios and must be taken into account when interpreting the results.

  • The degeneracy between the dust Colour Temperature and the spectral index
    Astronomy and Astrophysics - A&A, 2012
    Co-Authors: M. Juvela, N. Ysard
    Abstract:

    Context. With the current Herschel and Planck satellite missions, there is strong interest in the interpretation of the details of the sub-millimetre dust emission spectra. The data contain information on the properties of the interstellar clouds and the physics of the dust grains. A lot of work has been done to understand the negative correlation observed between the spectral index βObs and the Colour Temperature TC that in the χ2 fits is partly caused by the observational noise. Aims: In the (TC, βObs) plane, the confidence regions are elongated, banana-shaped structures. Previous studies have indicated that the errors may exhibit strongly asymmetric features that have important consequences for the investigation of individual objects and the interpretation of the relation between the TC and βObs parameters. We study under which conditions the confidence regions exhibit such anomalous, strongly non-Gaussian behaviour that could affect the interpretation of the observed (TC, βObs) relations. Methods: We examined a set of modified black body spectra and spectra calculated from radiative transfer models of filamentary interstellar clouds. We analysed simulated observations at discrete wavelengths between 100 μm and 850 μm. We performed modified black body fits and examined the structure of the χ2(TC, βObs) function of the fits. Results: We demonstrate cases where, when the signal-to-noise ratio is low, the χ2 has multiple local minima in the (TC, βObs) plane. A small change in the weighting of the data points can cause the solution to jump to completely different values. In particular, if there is noise, the analysis of spectra with T > 10 K and βObs ≲ 2 can lead to a separate population of solutions with much lower Colour Temperature and higher spectral indices. The anomalies are caused by the noise. However, the tendency to show multiple χ2 minima depends on the model (in part via the influence on the signal-to-noise ratios) and on the set of wavelengths included in the analysis. Deviations from the underlying assumption of a single modified black body spectrum are not significant. Conclusions: The presence of several local minima implies that the results obtained from the χ2 minimisation depend on the starting point of the optimisation and may correspond to non-global minima. Because of the strongly non-Gaussian nature of the errors, the obtained (TC, βObs) distribution may be contaminated by a few solutions with unrealistically low Colour Temperatures and high spectral indices. Proper weighting must be applied to avoid the determination of the βObs(TC) relation to be unduly affected by these measurements.

  • The degeneracy between the dust Colour Temperature and the spectral index The problem of multiple χ 2 minima
    Astronomy & Astrophysics, 2012
    Co-Authors: M. Juvela, N. Ysard
    Abstract:

    Context. With the current Herschel and Planck satellite missions, there is strong interest in the interpretation of the details of the sub-millimetre dust emission spectra. The data contain information on the properties of the interstellar clouds and the physics of the dust grains. A lot of work has been done to understand the negative correlation observed between the spectral index βObs and the Colour Temperature TC that in the χ 2 fits is partly caused by the observational noise. Aims. In the (TC, βObs) plane, the confidence regions are elongated, banana-shaped structures. Previous studies have indicated that the errors may exhibit strongly asymmetric features that have important consequences for the investigation of individual objects and the interpretation of the relation between the TC and βObs parameters. We study under which conditions the confidence regions exhibit such anomalous, strongly non-Gaussian behaviour that could affect the interpretation of the observed (TC, βObs) relations. Methods. We examined a set of modified black body spectra and spectra calculated from radiative transfer models of filamentary interstellar clouds. We analysed simulated observations at discrete wavelengths between 100 μm and 850 μm. We performed modified black body fits and examined the structure of the χ 2 (TC ,β Obs) function of the fits. Results. We demonstrate cases where, when the signal-to-noise ratio is low, the χ 2 has multiple local minima in the (TC ,β Obs )p lane. A small change in the weighting of the data points can cause the solution to jump to completely different values. In particular, if there is noise, the analysis of spectra with T > 10 K and βObs < 2 can lead to a separate population of solutions with much lower Colour Temperature and higher spectral indices. The anomalies are caused by the noise. However, the tendency to show multiple χ 2 minima depends on the model (in part via the influence on the signal-to-noise ratios) and on the set of wavelengths included in the analysis. Deviations from the underlying assumption of a single modified black body spectrum are not significant. Conclusions. The presence of several local minima implies that the results obtained from the χ 2 minimisation depend on the starting point of the optimisation and may correspond to non-global minima. Because of the strongly non-Gaussian nature of the errors, the obtained (TC ,β Obs) distribution may be contaminated by a few solutions with unrealistically low Colour Temperatures and high spectral indices. Proper weighting must be applied to avoid the determination of the βObs(TC) relation to be unduly affected by these measurements.