Catálogo de publicaciones - revistas

<jats:p> Numerous measurements have shown that the standard R classes do not represent adequately many road surfaces used nowadays. Therefore, the construction of portable reflectometers intended for on-site measurements of road surface reflection properties has been given particular attention during the last decade. This paper presents a new procedure for the improvement of the accuracy of such a portable reflectometer. Optimally extrapolating the values of the 20 luminance coefficients (q), each measured by the portable reflectometer for a set of angles of observation (α = 5°–80°), the 20 q-values referring to α = 1° are calculated. This enables their comparison with the corresponding q elements from each of the 447 reduced q-tables derived from the available r-table database, obtained by using a precise laboratory reflectometer on a wide variety of road samples. Selecting the closest reduced q-table, the corresponding r-table and the actual average luminance coefficient can be determined. In order to validate the proposed procedure, which can also be applied to other similar portable reflectometers, measurements of the luminance and overall and longitudinal luminance uniformities were carried out on eleven road-lighting installations. They showed that the results obtained by this procedure deviate only slightly from those obtained using r-tables determined by the laboratory reflectometer. </jats:p>

<jats:p> Application of the Commission Internationale de l’Eclairage system for mesopic photometry requires that an estimate is made of the observers’ state of luminance adaptation. This paper addresses an assumption made when estimating background luminance, a component of adaptation luminance. Specifically, using spatial sampling of the visual field we compare background luminances determined from assumptions of static or dynamic visual gaze, the former being a simplification, the latter being a better representation based on eye movements when driving. The comparison was undertaken with luminance images of urban scenes at night on three roads, two real and one simulated. It was found that background luminances were significantly higher when estimated using the dynamic assumption. It was also found that scene luminances at the point of foveal fixations tend to be higher than those luminances influencing peripheral regions of the retina. Compared with the background luminance estimated for a dynamic peripheral field, a horizon-centred 10° circle led to a slightly higher estimate and the road surface luminance to a slightly lower estimate of background luminance. </jats:p>

<jats:p> In this study, two psychophysical experiments, one on colour preference and the other on colour discrimination, were conducted. To investigate the colour preference for blue jeans, 27 subjects with normal colour vision were asked to rate their visual appreciation of seven pairs of jeans with a colour gradient pattern. Nine LEDs, with uniformly sampled correlated colour temperature (CCT) values ranging from 2500 K to 6500 K, were used to illuminate the jeans. These lights produced a constant illuminance of approximately 200 lux, and their colour rendering indexes were between 79 and 91. In addition, using a Farnsworth-Munsell (FM)-100 Hue Test, the blue-region colour discrimination of 42 observers was assessed for five LEDs of the same type but with different CCTs (2500 K–6500 K, 1000 K interval). The results indicate that there is an optimum CCT of 5500 K for jeans, at which observers were found to exhibit the greatest capability for colour discrimination and the highest rating for colour preference. Interestingly, a significant gender difference was found in this study, which had not been observed in our previous work with quite similar experimental settings but different experimental objects. The findings of this study should provide a deeper understanding for the lighting design of shopping malls for jeans. </jats:p>

<jats:p> The subjective impressions of pedestrians are necessary in order to decide on the appropriate colour of light to be used for street lighting. Therefore, a pilot project aimed to compare subjective evaluations of the sidewalk illumination under two street lighting installations, realised by LEDs of 3000 K (warm white) and 4000 K (neutral white), was recently conducted in Belgrade. Both installations had comparable sidewalk illuminances as well as other relevant photometric parameters. The evaluation was done through a questionnaire. A group of 139 (61 male and 78 female) respondents, all of them university students, was asked to grade both lighting installations for the sidewalk light intensity, the appearance of human faces, the colour of light and the colour rendering as well as the overall impression. According to the median values, the 3000 K LED installation was considered better than the 4000 K installation for all aspects assessed as well as the overall impression. Although the survey results convincingly showed a preference for 3000 K LEDs for this comparison, additional research is needed using a more representative sample of people and a wider range of locations before a definite conclusion can be reached. </jats:p>

<jats:p> In today's world, light-emitting diodes are quickly replacing conventional light sources, both indoors and outdoors. Being a solid-state device, adverse ambient conditions such as high temperature and humidity lead to its poor performances, light quality and longevity. In outdoor applications, exposure to high ambient temperature during daytime, even when the lamp power is off, causes the lamp performance to deteriorate. In tropical countries, the environmental temperature in most of the days is higher than 25℃ and sometimes reaches 50℃. Here, the humidity varies between 30% and 80% and frequently over 80%. Thus, the reliability of the light emitting diodes is a question that needs a thorough study. In line with this, in this study, an effort has been made through an experiment. Here, commercially available surface-mounted device and chip-on-board-based light-emitting diodes are tested through an environmental chamber, and their measured illuminance values were observed by varying the relative humidity. Then, the temperature ageing or stress was set at 60℃ on the above types of light-emitting diodes at power off condition for 6000 hours and after that its luminous flux and spectral distribution were observed. The degradation observed under these conditions may guide designers and manufacturers to upgrade their lighting systems to make them fit for tropical conditions. </jats:p>

<jats:p> Light is considered the most important environmental factor for greenhouse crops, and lack of lighting limits the productivity of greenhouses. Many studies have focused on improving the energy efficiency of lighting in agriculture. In this study, LED lights were mounted in the top, middle and bottom of the plant canopy to provide additional photosynthetically active radiation. Assuming that 100% of the predicted outdoor radiation is available, the canopy light distribution model was used to determine the relationship between the light energy consumption and the optimal yield. Decision-making on lighting scheduling may be considered as a constrained optimisation, and the status of the LEDs in a period acts as the decision variable. Besides, there are two objective functions: one is the energy consumed by the LED device; the other is the expected yield calculated by the crop model of tomatoes. The optimal solution of the multi-objective optimisation is not unique but corresponds to an infinite number of yield/energy combinations. Farmers can select these combinations according to additional restrictions such as energy efficiency ratio or photoperiod. The yield of our strategy was increased by 12.3% under the constraint of equal energy consumption compared to the greenhouse threshold control strategy. Given the same output as the constraint, the energy consumption was reduced by 30.1%. </jats:p>

<jats:p> LED lighting is the most promising lighting technology of the current era because it is highly reliable and energy efficient. The reliability of an LED luminaire is dependent primarily on its junction temperature in operation. Since LED luminaire design differs across manufacturers, a generalised experimental procedure and simplified model is adapted to estimate the junction temperature of an LED luminaire. The results are analysed, and the model is validated with an experimental study on two different luminaires. Further, to analyse the effect of junction temperature on the light output, a novel model and methodology are adopted such that light output can be estimated for any operating temperature, if the light output at a reference temperature is known. Three models were selected to estimate the light output at different temperatures, and four different LEDs were selected for the experimental study. A linear model for the thermal multiplier is selected as the best model to estimate the light output at a desired temperature and is validated using statistical tools. Thus, this simple model and generalised experimental procedures will help in estimating the effect of junction temperature on the performance of LED luminaires. </jats:p>

<jats:p> The paper reports a study that examines how to determine if a road traffic collision took place in daylight or in the dark. An innovative method was developed, based on solar altitude, to establish cut-off points of daylight and darkness determined from a study of daylight availability in England, Scotland and Wales. This approach provides a rigorous method to differentiate daytime and night-time collisions. The criteria were used in a study of the collisions reported in the STATS19 data set for the weeks either side of the clock changes that are necessary between Greenwich Mean Time and British Summer Time. By comparing periods with the same clock time either side of the time change, using the aforementioned method, it was possible to isolate collisions within the same time period that during one week occurred in darkness and in the other week in daylight. The initial finding was that there are 19.3% more collisions in the dark periods and there is an even greater increase (31.7%) in pedestrian injuries. </jats:p>

<jats:p> Definition of the growth and development characteristics of plants in varied light conditions is a key factor for the creation of highly efficient light facilities for plant cultivation. Experimental research was conducted using an LED irradiation facility with photosynthetic photon flux densities ranging from 0 to 261 μmol m<jats:sup>−2</jats:sup> s<jats:sup>−1</jats:sup> and a continuous spectrum with maxima at 445 and 600 nm. Under the maximum photosynthetic photon flux density (261 μmol m<jats:sup>− 2 </jats:sup> s<jats:sup>−1</jats:sup>) wheat germs demonstrated diminishing leaf surface with high values of specific leaf area, enhanced pubescence of ground tissues, increases in the number of stomata on the upper epidermis and palisade, and an increase in the thickness of the leaves as well as an increase in carotenoids but a decrease in the chlorophyll a+b/carotenoids relation. It was revealed that the optimum level of photosynthetic photon flux density for the referred spectrum was in the range from 82 to 100 µmol m<jats:sup>−2</jats:sup> s<jats:sup>−1</jats:sup>, which may enable a reduction of irradiance under specific conditions during early development with no harm to the plants while minimizing energy consumption during cultivation. </jats:p>

<jats:p> Light's impact on many crop species and vegetables has been deeply studied in recent years but there are still some economic and technical issues to overcome. Thus, the impact of light spectrum and photosynthetic photon flux density from light-emitting diodes on the germination and seedling emergence of Okra has been investigated in this study. Different light treatments have been applied to Okra seeds using a factorial design of three levels of light spectrum and three levels of photosynthetic photon flux density; these three levels of light spectrum are defined by their peak wavelengths at 635 nm (R<jats:sub>635</jats:sub>), 457 nm (B<jats:sub>457</jats:sub>) and 521 nm (G<jats:sub>521</jats:sub>) and are, respectively, in the red, blue and green region of the visible spectrum; levels of photosynthetic photon flux density are 100 µmol m<jats:sup>−2</jats:sup> s<jats:sup>−1</jats:sup>, 200 µmol m<jats:sup>−2</jats:sup> s<jats:sup>−1</jats:sup> and 300 µmol m<jats:sup>−2</jats:sup> s<jats:sup>−1</jats:sup>. Results show significant interactions between light spectrum and photosynthetic photon flux density on mean germination time, mean germination rate, uncertainty of germination and seedling emergence height. R<jats:sub>635</jats:sub> shows a better mean germination rate and less uncertainty and dispersion than B<jats:sub>457</jats:sub> and G<jats:sub>521</jats:sub>. Seedlings that emerged under photosynthetic photon flux density of 300 µmol m<jats:sup>−2</jats:sup> s<jats:sup>−1</jats:sup> are significantly shorter than those that emerged under 100 µmol m<jats:sup>−2</jats:sup> s<jats:sup>−1</jats:sup> and 200 µmol m<jats:sup>−2</jats:sup> s<jats:sup>−1</jats:sup>. </jats:p>