LRT Digest 3: New colour metrics and their use

This paper is concerned with designing light source spectra for optimum luminous efficacy and colour rendering. We demonstrate that it is possible to design light sources that can provide both good colour rendering and high luminous efficacy by combining the outputs of a number of narrowband spectral constituents. Also, the achievable results depend on the numbers and wavelengths of the different spectral bands utilized in the mixture. Practical realization of these concepts has been demonstrated in this pilot study which combines a number of simulations with tests using real LEDs (light emitting diodes). Such sources are capable of providing highly efficient lighting systems with good energy conservation potential. Further research is underway to investigate the practicalities of our proposals in relation to large-scale light source production.

The purpose of this investigation is to quantify the influence of the peak wavelength shifts in commercially available LEDs on the characteristics of the mixed-LED white-light sources. For this purpose, a tetrachromatic spectrum was optimized and then subjected to deviations in the peak wavelengths. A total of 882 combinations of peak wavelength values were evaluated, and the results are reported in terms of correlated colour temperature, colour-rendering properties, and radiant luminous efficacy. The results show that there can be significant changes in the characteristics of the source under these conditions. Such changes are highly likely to present problems when dealing with applications where an effective and accurate white-light source is important.

This study attempts to simulate the metamerism colour, and the guava was used as the target object. We design four sets of metamers with a correlated colour temperature of 4000K and an illuminance of 750lux. The light source was simulated in the LED cube. The subjects with convenience sampling observed the visual effects, including look delicious, colourful, and colour rendering of guava under metamerism, then analysed its relationship with CRI and CQS. The results showed that colour rendering and visual effects are not a positive relationship, and the effect of CQS is closer to the visual effects of the subjects. The results of this study can be used as a reference for light source lighting designers as a basis for improving lighting conditions. In the future, we can collect databases for the different objects with an optimized multi-spectral light source.

The advent of the LED light source has promoted the concept of human-centric lighting (HCL). The LED has also been responsible for increases in the electrical efficiency of lighting systems, coupled with recent improvements in their colour properties. We have found that it is also possible to create a lit environment with enhanced clinical attributes by providing a source spectrum that meets the requirements of the Cyanosis Observation Index (COI). This paper describes the use of a differential evolution (DE) algorithm for the spectral design of a mixed LED light source capable of meeting COI recommendations as well as HCL performance criteria.

Lighting is one of the basic aspects that eases our lives and increases its quality. We use lighting tools in many places such as homes, streets, work places, hospitals, factories, etc. In this study, the effects of the light source and the surface of the object on features like colour temperature, glare, colour (perceived) and dominant wavelength is analysed. Four light sources such as a warm white halogen lamp, warm white LED source and two cool white LED sources were used. In the light measurements, 10 paper surfaces and 8 cloth surfaces were selected as the surface type. Colours of the surfaces were selected among the main colours on the colour locus. Light, reflected from surface was recorded with Konica Minolta CS-200 model. All results were indicated and compared with each other.

Light from the polymerization source which initiates photopolymerization in the material has its determined wavelength. Photoinitiator, such as camphorhinone, excited by light, can be activated with any of the wavelength from its absorption spectrum. To obtain successful photopolymerization, light source should emit waves of adequate wavelength; light intensity has to be optimal, to have sufficient time of exposure and material up to 2 mm thickness. Photoinitiator inside the material should match light source spectrum and work regime. Halogen lamps have wide spectra of wavelengths in the visible part of the light spectrum. Their spectra are similar to absorption spectrum of camphorhinone. Plasma (xenon) lamps emit blue light. Though their diapason is low, spectra have great intensity. Adequate diapason and easy excitation allow them to have short time of exposure. LED lamps have blue diodes as light source. They do not need filters due to narrow emission spectrum. Laser (argon) lamps are the only that emit linear spectra. Ultraviolet (mercury) lamps are not in use any more in dentistry; theirs initiators were activated by UV light. LED lamps have longer life time; do not change the spectra during time, warm less, do not need filters, allow change of the source for more powerful, more efficient and more advantageous two steps or impulse illumination mode. However, LED lamps can not be used for a material that has photoinitiator(s) activated by light with wavelength above the maximum of the LED spectra.

The higher the colour fidelity of a light source, the lower its luminous efficacy of radiation because the light source spectrum must deviate from V(λ) to deliver the higher fidelity. Two experiments probed the trade-off between energy efficiency and colour quality. Experiment 1 required participants to simultaneously view pairs of light sources differing in colour fidelity, at either a higher (346 lx) or lower (277 lx) illuminance. Participants performed a timed reading task and judged the colour appearance of the pair. There were no effects of illuminance, but larger colour fidelity differences between the light sources in the pair correlated with lower appearance judgements. Experiment 2 simulated the effect of light sources on defined reflectance spectra. The results showed that improvements of colour fidelity above what is often considered satisfactory can yield more satisfying illumination while using the same amount of power.

The article focuses on the measurement of lighting characteristics of exhibited items in the exhibition halls of the two largest Russian museums – the State Hermitage and the State Tretyakov Gallery. The review of the current regulatory technical documentation for the design and implementation of museum lighting is given, the shortcomings are identified and the proposals for improving the legal framework for the lighting of the exhibited items are made. The measurements were carried out in accordance with existing recommendations, and according to which the lighting was designed in the museums. The principal measured parameters in this survey were UV radiation, illuminance of exhibited items, luminance distribution in the viewer’s field of view, correlated colour temperature and the colour rendering index of the light sources. A brief overview of the measurement results of some halls of selected museums is given.

This paper presents an experiment on the effect of light on the perception of paintings. The experiment was performed in a test-room where a typical museum exhibition set-up was simulated. Two different paintings were shown to 44 participants, under different light scenes obtained by using tuneable LED (Light Emitting Diode) wallwashers. To set the light scenes, the following parameters were modified: correlated colour temperature of the lighting, illuminance on the painting and the colour of the background wall. Participants answered a questionnaire to assess the perception of the paintings’ colours, the lighting conditions and the pleasantness of the exhibition set-up. The results demonstrated that illuminance is the parameter mainly affecting perception, for both paintings. However, correlated colour temperature and wall colour, as well as the combination of the three different considered parameters, can more or less influence perception depending on the chromatic composition of the painting.