The effect of age on white light perception.

The way that persons from different age groups experience “white light” is investigated. Human eye lens transmission changes spectrally with age and this may influence the way that humans from different ages experiences light. Such a difference may be important in industrial and medical environments. Two different age groups, one group younger than 40 years of age and another group older than 50 years of age were subjected to the same “white” definition task. A conventional single-booth setup was used where observers were able to adjust the intensity of four coloured LED’s. Results of the psychophysical test procedure were used to generate specifications of two light sources, as selected by the two age groups. The two age groups selected two very different light sources when tasked to achieve a “perception” of white. Results show that the older group prefers a source with a colour rendering index number of 89 and the younger group prefers a source with a colour rendering index number of 74. The sources selected by the two age groups specifies correlated colour temperature values of 5150 K for the older age group and 6592 K for the younger group

Structural and Compositional Analysis of Feathers of Sunbird Nectarinia Asiatica

The plumage of many birds is highly attractive, especially when thefeathers are patterned in strongly contrasting colours. Orange colours are generally caused by pigments that selectively absorb short-wavelength light. When these pigments are embedded in a diffusive medium, only the long-wavelength part of incident broadband light is reflected and scattered. In contrast, blue or green animal coloration is virtually always due to periodic structures that reflect and scatter incident light of a restricted short-wavelength range(Srinivasarao, 1999; Vukusic and Sambles, 2003; Kinoshita and Yoshioka, 2005; Prum, 2006). Pigmentary and structural coloration are often found simultaneously, not only in birds but also in many other animals, for example butterflies, beetles and lizards (Kinoshita,2008). Birds possess various pigment classes, for instance carotenoids, pterins, porphyrins, psittacofulvins and melanins (McGraw, 2006; Hill and McGraw, 2006), and various mechanisms of structural colouration, namely thin films, multilayers, photonic crystals, keratin spongy nanostructures and nanofibres (e.g. Durrer, 1977; Shawkey et al., 2003;Shawkey et al., 2006; Yoshioka et al., 2007; Doucet and Meadows, 2009; Prum et al., 2009; Stavenga et al., 2010; D’Alba et al., 2011). The predominant location of colouration is the feathers, often either the barbs or the barbules. Structural coloration of avian skin have been long hypothesized to be produced by incoherent(Rayleigh /Tyndall )scattering. Avian plumage color have emerged recently as model system for investigating the type of information that can be signaled by showy sexual display in birds.The non pigmentary colors of the tissues of living organism are produced by physical interaction of light with nanostructures in the tissues. The brilliant iridescent color appearances of many avian feathers are produced by complex optical phenomena. They principally arise from coherent light scattering from self-assembled quasi-ordered structures that have a spatially periodic variation in refractive index. Iridescent structural colors in biology exhibit sophisticated spatially-varying reflectance properties that depend on both the illumination and viewing angles. The classification of such spectral and spatial information in iridescent structurally colored surfaces is important to elucidate the functional role of irregularity and to improve understanding of color pattern formation at different length scale

Characterization and reliability of blue and white GaN-based LEDs submitted to current and thermal stress

The aim of this thesis work is to analyze reliability of blue and white GaN-based commercial LEDs. Reliability is indeed one of the key factors for devices success in the market of lighting solutions. Temperature and driving current are the main causes of degradation of LEDs. In order to understand the degradation mechanisms of these devices two types of stresses have been carried out, current and thermal stress and pure thermal stress, and electrical, optical and thermal measurements have been performed. The results obtained at the end of this work show several types of degradation mechanisms which influence LEDs both electrical and optical properties / Caratterizzazione e affidabilità di LED blu e bianchi basati su nitruro di gallio sottoposti a stress in corrente ed in temperatur

Color vision in the comb frequency domain

In 1982, Horace Barlow considered the question of human trichromacy in the context of information theory: according to the Sampling Theorem, three types of receptors covering the visible spectrum (400- -700 nm) might be sufficient to reconstruct the color signal. Although Barlow was led to reject the direct application of the Sampling Theorem to explain color dimensionality, the theoretical framework offers a fresh point of view for analyzing the color system in conjunction with the physical characteristics of natural color signals. This review aims to illustrate that if the strict mathematical reconstruction (as implied by the Sampling Theorem) is replaced by a pragmatic approximation of color signals, then trichromacy, with its subsequent opponent-color process, could be regarded as an optimization of color constancy abilities in the spectral environment of primates. Higher dimension systems (tetrachromacy) found in other species can also serve the purpose of color constancy optimization in environments where color signals exhibit a finer spectral structure

Study of the reliability of power LEDs for color mixing applications

The aim of this thesis is the reliability analysis of high-power RGB and white LEDs\nprovided by six different manufacturers. In order to evaluate the characteristics of these devices in terms of lifetime and optical power maintenance combined thermal and current stress tests have been carried out, verifying the changes of the optical and electrical characteristics of the devices during\nthe stress. The results of this work have revealed several types of degradation of various\ndevices

Image calibration and analysis toolbox: a free software suite for objectively measuring reflectance, colour and pattern

Article"This is the pre-peer reviewed version of the following article: Image Calibration and Analysis Toolbox – a free software suite for objectively measuring reflectance, colour and pattern, which has been published in final form at http://onlinelibrary.wiley.com/doi/10.1111/2041-210X.12439/abstract. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving."1.Quantitative measurements of colour, pattern, and morphology are vital to a growing range of disciplines. Digital cameras are readily available and already widely used for making these measurements, having numerous advantages over other techniques, such as spectrometry. However, off-the-shelf consumer cameras are designed to produce images for human viewing, meaning that their uncalibrated photographs cannot be used for making reliable, quantitative measurements. Many studies still fail to appreciate this, and of those scientists who are aware of such issues, many are hindered by a lack usable tools for making objective measurements from photographs. 2.We have developed an image processing toolbox that generates images that are linear with respect to radiance from the RAW files of numerous camera brands, and can combine image channels from multispectral cameras, including additional ultraviolet photographs. Images are then normalised using one or more grey standards to control for lighting conditions. This enables objective measures of reflectance and colour using a wide range of consumer cameras. Furthermore, if the camera's spectral sensitivities are known, the software can convert images to correspond to the visual system (cone-catch values) of a wide range of animals, enabling human and non-human visual systems to be modelled. The toolbox also provides image analysis tools that can extract luminance (lightness), colour, and pattern information. Furthermore, all processing is performed on 32-bit floating point images rather than commonly used 8-bit images. This increases precision and reduces the likelihood of data loss through rounding error or saturation of pixels, while also facilitating the measurement of objects with shiny or fluorescent properties. 3.All cameras tested using this software were found to demonstrate a linear response within each image and across a range of exposure times. Cone-catch mapping functions were highly robust, converting images to several animal visual systems and yielding data that agreed closely with spectrometer-based estimates. 4.Our imaging toolbox is freely available as an addition to the open source ImageJ software. We believe that it will considerably enhance the appropriate use of digital cameras across multiple areas of biology, in particular researchers aiming to quantify animal and plant visual signals

Light-emitting diodes enhanced by localized surface plasmon resonance

Light-emitting diodes [LEDs] are of particular interest recently as their performance is approaching fluorescent/incandescent tubes. Moreover, their energy-saving property is attracting many researchers because of the huge energy crisis we are facing. Among all methods intending to enhance the efficiency and intensity of a conventional LED, localized surface plasmon resonance is a promising way. The mechanism is based on the energy coupling effect between the emitted photons from the semiconductor and metallic nanoparticles fabricated by nanotechnology. In this review, we describe the mechanism of this coupling effect and summarize the common fabrication techniques. The prospect, including the potential to replace fluorescent/incandescent lighting devices as well as applications to flat panel displays and optoelectronics, and future challenges with regard to the design of metallic nanostructures and fabrication techniques are discussed

An Analytical model for the colorimetric characterization of color CRTs

To be a viable instrument for color appearance research, the color Cathode Ray Tube has to be very well calibrated and characterized. The purpose of this research was to develop the techniques and methods used to carry out such characterization, and also to evaluate to what degree of precision and accuracy can such a characterization be performed. A new model for predicting the CRT behavior is presented along with the experimental results that validate it

Optimising Light Source Spectrum to Reduce the Energy Absorbed by Objects

Light is used to illuminate objects in the built environment. Humans can only observe light reflected from an object. Light absorbed by an object turns into heat and does not contribute to visibility. Since the spectral output of the new lighting technologies can be tuned, it is possible to imagine a lighting system that detects the colours of objects and emits customised light to minimise the absorbed energy. Previous optimisation studies investigated the use of narrowband LEDs to maximise the efficiency and colour quality of a light source. While these studies aimed to tune a white light source for general use, the lighting system proposed here minimises the energy consumed by lighting by detecting colours of objects and emitting customised light onto each coloured part of the object. This thesis investigates the feasibility of absorption-minimising light source spectra and their impact on the colour appearance of objects and energy consumption. Two computational studies were undertaken to form the theoretical basis of the absorption-minimising light source spectra. Computational simulations show that the theoretical single-peak spectra can lower the energy consumption up to around 38 % to 62 %, and double-peak test spectra can result in energy savings up to 71 %, without causing colour shifts. In these studies, standard reference illuminants, theoretical test spectra and coloured test samples were used. These studies are followed by the empirical evidence collected from two psychophysical experiments. Data from the experiments show that observers find the colour appearance of objects equally natural and attractive under spectrally optimised spectra and reference white light sources. An increased colour difference, to a certain extent, is found acceptable, which allows even higher energy savings. However, the translucent nature of some objects may negatively affect the results