Colour Appearance Modelling for Self-luminous Colours

An experimental setup and procedure for the evaluation of self- luminous colours viewed against both dark and luminous backgrounds is presented. Physical and visual data of self-luminous colours is gathered in order to develop a Colour Appearance Model for self-luminous colours under different viewing conditions. This model is needed for the evaluation of light sources. This record was migrated from the OpenDepot repository service in June, 2017 before shutting down

Comment Concerning the Effects of Light Intensity on Melatonin Suppression in the Review “Light Modulation of Human Clocks, Wake, and Sleep” by A. Prayag et al.

Dose-response curves for circadian phase shift and melatonin suppression in relation to white or monochromatic nighttime illumination can be scaled to melanopic weighed illumination for normally constricted pupils, which makes them easier to interpret and compare. This is helpful for a practical applications

Converter-connected distributed generation units with integrated harmonic voltage damping and harmonic current compensation function

The steadily growing share of converter-connected distributed generators, combined with a large amount of nonlinear and unbalanced loads connected to the electric power system, has led to a degraded power quality. Both harmonic voltage and harmonic current distortion may cause many unfavourable effects on the power system. However. the converter-connected distributed generators can be redesigned to have a positive effect on the distortion of the grid voltage. Two different approaches call be discerned. At the one hand, distributed generation units can be controlled to synthesize a resistive load for harmonic voltage components. This approach is called harmonic voltage damping. At the other hand, if the polluting current of an adjacent nonlinear load is measured and added to the control loop, the converter-connected distributed generator is able to compensate all harmonic current components of the nonlinear load. This approach is referred to as harmonic current compensation. In this paper, a control strategy for a converter-connected distributed generator is extended with a harmonic voltage damping function and a harmonic current compensation function. Experimental tests show that the voltage distortion of the grid voltage can be significantly improved. (C) 2008 Elsevier B.V. All rights reserved

Correlation between colour quality metric predictions and visual appreciation of light sources

Over the past years there has been increasing evidence that the CIE color rendering index Ra fails to correspond to the perceived color quality of many light sources, especially some Light-Emitting-Diodes. Several proposals to update, complement or even replace the CIE Ra have therefore been made. The performance of thirteen color quality metrics was evaluated by calculating the average correlation of the metric predictions with the visual scaling of the perceived color quality obtained in several psychophysical studies. Two aspects of perceived color quality were investigated, appreciation (preference or attractiveness) and naturalness. The memory color quality metric (Sa) of Smet et al. was found to correlate highly with perceived appreciation (r = 0.88). It was found to be statistically better (p<0.0001) at it than all other metrics. The CIE Ra performed the worst. A metric that combines the gamut area index (GAI) and the CIE Ra using an arithmetic mean correlated highly with the perceived naturalness of a light source (r = 0.85). It was found to be statistically better at predicting naturalness than all other metrics (p<0.0001). A negative correlation was found, between the capabilities of a light source‘s ability to predict appreciation and naturalness, indicating that a complete description of the color quality of a light source probably requires more than one metric.status: publishe

Optimization of colour quality of solid-state lighting based on memory colours

Simulated and real tri- and tetrachromatic Light-Emitting-Diode (LED) clusters were optimized for luminous efficacy of radiation (LER) and the memory colour quality metric developed by the authors. The simulated clusters and real clusters (composed of commercially available LEDs), respectively showed no significant and substantial differences between the different cluster types investigated. The real clusters also exhibited a large drop in LER and colour quality compared to the simulated clusters due to the limited range of available peak wavelengths and spectral halfwidths. A real tetrachromatic LED lamp, constructed with commercial red, green, blue and warm white LEDs, was optimized for LER and colour quality. In a psychophysical experiment, the colour quality of the LED lamp (optimized for 2700 K) and an incandescent lamp was assessed by 18 observers. The visual appreciation (in terms of attractiveness, preference and memory colour similarity) of the LED lamp was rated significantly higher than the incandescent lamp.status: publishe

Optimization of colour quality of LED lighting with reference to memory colours

Simulated and real tri- and tetrachromatic light-emitting-diode (LED) clusters were optimized for luminous efficacy of radiation (LER) and the memory colour quality metric developed by the authors. The simulated clusters showed no significant differences in achievable colour quality and LER between the different cluster types investigated. The real clusters (composed of commercially available LEDs) showed substantial differences in achievable colour quality and LER between the different cluster types investigated. The real clusters also exhibited a large drop in LER and memory colour quality compared to the simulated clusters due to the limited range of available peak wavelengths and spectral halfwidths. A real tetrachromatic LED lamp, constructed with commercial red, green, blue and warm white LEDs, was optimized for LER and colour quality. In a psychophysical experiment, several aspects of the colour quality of the LED lamp (optimized for 2700 K) and an incandescent lamp were assessed by eighteen observers. The visual appreciation (in terms of attractiveness, preference and memory colour similarity) of the LED lamp was rated significantly higher than the incandescent lamp.status: publishe

Thermal characterization of single-die and multi-die high power light-emitting diodes

The forward voltage for single-die high-power light-emitting diodes (LEDs) driven at currents within a specific current interval is proportional to the diode junction temperature T. This correlation can be used to determine junction temperatures in lots of practical applications. However, multi-die high-power LED modules with multiple series or parallel connections of diode chips are believed to have a much greater potential to be used in general lighting than single-die packages. The current-voltage characteristics of a variety of multi-die LEDs, ranging from two to a few hundred dies, are recorded at different ambient temperatures. The results are used to model the forward voltage as a function of a generalized junction temperature. In multi-die LED modules these models allow analogous junction temperature determination as in single-die packages. The influence of drive current and drive mode (DC or PWM) on junction temperature is examined and compared for both single-die and multi-die packages. Apparently, junction temperature only significantly increases when a certain current level is exceeded, depending on the internal series resistance of the complete LED package. Moreover, combining models for single-die and multi-die LEDs allows for the characterization of thermal interactions between different dies of multi-die packages, whether they are switched on or not. The junction temperature of separate LED dies in multi-die modules can then be predicted and used for further diode characterization.status: publishe

Brightness perception of unrelated self-luminous colors

The perception of brightness of unrelated self-luminous colored stimuli of the same luminance has been investigated. The Helmholtz–Kohlrausch (H-K) effect, i.e., an increase in brightness perception due to an increase in saturation, is clearly observed. This brightness perception is compared with the calculated brightness according to six existing vision models, color appearance models, and models based on the concept of equivalent luminance. Although these models included the H-K effect and half of them were developed to work with unrelated colors, none of the models seemed to be able to fully predict the perceived brightness. A tentative solution to increase the prediction accuracy of the color appearance model CAM97u, developed by Hunt, is presented.Also published in The Virtual Journal for Biomedical Optics vol:8 issue:7 (ISSN 1931-1532)status: publishe

Performances of Compact Fluorescent Lamps With Integrated Ballasts and Comparison With Incandescent Lamps

The saving potential of electrical energy for lighting in housing is very high. With the first phase of the European regulation on the production and sale of non-effective incandescent lamps having just come into effect, it appears that the use of compact fluorescent lamps (CFL) becomes an important topic. For that reason, this paper lists the major barriers to the spread of compact fluorescent lamps in housing and analyses four of them. 16 compact fluorescent lamps were measured in a laboratory in order to study their warm-up time, their colour shift during warm-up, the impact of their position on their luminous flux and their light output equivalent, in comparison to two incandescent lamps. Measurements show that information given on the lamp package is incomplete and inaccurate. The 1:5 rule, currently applied by European manufacturers in order to calculate the power of a CFL replacing an incandescent lamp, is inappropriate. A ratio of 1:4 would be better. While it has been observed that the position of the lamp base has an impact of the lamp efficacy, it was impossible to predict which position is best. The run-up time of compact fluorescent lamp can be long and depends on the shape of the lamp. The lamp colour modification during run-up is visible and can be a barrier to the use of compact fluorescent lamps. Tube CFLs should be favored as they have a higher luminous efficacy and take less time to reach their nominal flux. Finally, the measurements did not show any correlation between the lamp price and their quality