Low-cost extra-low voltage LED dimmer for tuneable white lighting

The colour appearance of light sources has a major impact on how people perceive space. With LED illumination lighting, the colour output can be tuned to virtually any perceivable colour, including any hue of white light. It has been established that the right shade of white light during the 24-hour day cycle has a positive effect on the human body's biological system. For this reason, it is very important to focus on the development and application of new lighting systems that have dynamically variable light outputs in order to imitate the sunlight. Circadian regulation is most responsive to short-wavelength light (460 nm = blue colour). This paper describes the development of a low-cost extra-low voltage LED dimmer for tunable white lighting systems aiming to achieve maximum electrical performance and light-output. This dimming module has two independent LED control channels and allows for a variable colour temperature control from warm white to cold white light. Experimental results of the dimming module efficiency measurements, correlated colour temperature (CCT), colour rendering index (CRI), illuminance and power consumption of the luminaire depending on the duty cycle for different control frequencies (200 Hz, 1.5 kHz, 5 kHz, 10 kHz and 20 kHz) are presented. The paper further describes the principle of creating control curves for an independent regulation of correlated colour temperature and illuminance. In the form of a table, the control curve outputs may be uploaded into a microcontroller. The paper details the construction, function and the advantages of this LED dimmer prototype.Web of Science253494

Effect of selected luminescent layers on CCT, CRI, and response times

Phosphors have been used as wavelength converters in illumination for many years. When it is excited with blue light, the frequently used yttrium aluminium garnet doped with cerium (YAG:Ce) phosphor converts a part of blue light to a wideband yellow light, resulting in the generated light having a white color. By combining an appropriate concentration of the YAG:Ce phosphor and blue excitant light, white light of a desired correlated color temperature (CCT) can be obtained. However, this type of illumination has a lower color rendering index value (CRI). In an attempt to improve the CRI value, we mixed the YAG:Ce phosphor with europium-doped calcium sulfide phosphor (CaS:Eu), which resulted in a considerably increased CRI value. This article examines an experiment with luminescent layers consisting of a mixture of selected phosphors and polydimethylsiloxane (PDMS). Different thicknesses in these layers were achieved by changing the speed of rotation during their accumulation onto laboratory glass using the method of spin coating. The spectral characteristics of these luminescent layers as they were excited with blue light emitting diode (LED) and laser diode (LD) were then determined. A suitable combination of the YAG:Ce phosphor with a phosphor containing europium, as it was excited with a blue LED, yielded a source of white light with a CRI value of greater than 85. The response time in the tested luminescent layers to a rectangular excitant impulse (generated by a signal generator and transmitted by LD) was also measured in order to examine their potential use in visible light communications (VLC).Web of Science1213art. no. 209

Preparation of N-doped carbon dots based on starch and their application in white LED

N-doped carbon dots (CDs) were synthesized simply and economically by a one-step hydrothermal method using starch as a carbon source and ethylenediamine (EDA) as a nitrogen dopant. The prepared CDs possess the properties of excitation-wavelength dependence and emit blue fluorescence under the excitation wavelength of 365 nm. CDs/starch composite was prepared to achieve the solid-state emission of CDs and their application in light emitting diode (LED) as fluorescent materials. White LED, with CIE coordinates of (0.33, 0.37) and correlated color temperature of 5462 K, was obtained by combining CDs/starch and ultraviolet LED light source, indicating that starch-based CDs have the promising potential in the field of optoelectronic devicesPeer reviewe

The effect of cave illumination on bats

Artificial light at night has large impacts on nocturnal wildlife such as bats, yet its effect varies with wavelength of light, context, and across species involved. Here, we studied in two experiments how wild bats of cave-roosting species (Rhinolophus mehelyi, R. euryale, Myotis capaccinii and Miniopterus schreibersii) respond to LED lights of different colours. In dual choice experiments, we measured the acoustic activity of bats in response to neutral-white, red or amber LED at a cave entrance and in a flight room – mimicking a cave interior. In the flight room, M. capaccinii and M. schreibersii preferred red to white light, but showed no preference for red over amber, or amber over white light. In the cave entrance experiment, all light colours reduced the activity of all emerging species, yet red LED had the least negative effect. Rhinolophus species reacted most strongly, matching their refusal to fly at all under any light treatment in the flight room. We conclude that the placement and light colour of LED light should be considered carefully in lighting concepts for caves both in the interior and at the entrance. In a cave interior, red LED light could be chosen – if needed at all – for careful temporary illumination of areas, yet areas important for bats should be avoided based on the precautionary principle. At cave entrances, the high sensitivity of most bat species, particularly of Rhinolophus spp., towards light sources almost irrespective of colour, calls for utmost caution when illuminating cave entrances

Visible Light Communication Using a Blue GaN μLED and Fluorescent Polymer Color Converter

This letter presents a novel technique to achieve high-speed visible light communication (VLC) using white light generated by a blue GaN mu LED and a yellow fluorescent copolymer. We generated white light suitable for room illumination by optimizing the ratio between the blue electroluminescence of the mu LED and yellow photoluminescence of the copolymer color converter. Taking advantage of the components' high bandwidth, we demonstrated 1.68 Gb/s at a distance of 3 cm (at 240 lx illumination). To the best of our knowledge, this is the fastest white light VLC results using a single blue LED/color converter combination.PostprintPeer reviewe

Implications for the protection of nocturnal migrants

The replacement of conventional lighting with energy‐saving light emitting diodes (LED) is a worldwide trend, yet its consequences for animals and ecosystems are poorly understood. Strictly nocturnal animals such as bats are particularly sensitive to artificial light at night (ALAN). Past studies have shown that bats, in general, respond to ALAN according to the emitted light color and that migratory bats, in particular, exhibit phototaxis in response to green light. As red and white light is frequently used in outdoor lighting, we asked how migratory bats respond to these wavelength spectra. At a major migration corridor, we recorded the presence of migrating bats based on ultrasonic recorders during 10‐min light‐on/light‐off intervals to red or warm‐white LED, interspersed with dark controls. When the red LED was switched on, we observed an increase in flight activity for Pipistrellus pygmaeus and a trend for a higher activity for Pipistrellus nathusii. As the higher flight activity of bats was not associated with increased feeding, we rule out the possibility that bats foraged at the red LED light. Instead, bats may have flown toward the red LED light source. When exposed to warm‐white LED, general flight activity at the light source did not increase, yet we observed an increased foraging activity directly at the light source compared to the dark control. Our findings highlight a response of migratory bats toward LED light that was dependent on light color. The most parsimonious explanation for the response to red LED is phototaxis and for the response to warm‐white LED foraging. Our findings call for caution in the application of red aviation lighting, particularly at wind turbines, as this light color might attract bats, leading eventually to an increased collision risk of migratory bats at wind turbines

The LED Paradox: How Light Pollution Challenges Experts to Reconsider Sustainable Lighting

In the 21st century, the notion of “sustainable lighting” is closely associated with LED technology. In the past ten years, municipalities and private light users worldwide have installed light-emitting diodes in urban spaces and public streets to save energy. Yet an increasing body of interdisciplinary research suggests that supposedly sustainable LED installations are in fact unsustainable, because they increase light pollution. Paradoxically, blue-rich cool-white LED lighting, which is the most energy-efficient, also appears to be the most ecologically unfriendly. Biologists, physicians and ecologists warn that blue-rich LED light disturbs the circadian day-and-night rhythm of living organisms, including humans, with potential negative health effects on individual species and whole ecosystems. Can the paradox be solved? This paper explores this question based on our transdisciplinary research project Light Pollution—A Global Discussion. It reveals how light pollution experts and lighting professionals see the challenges and potential of LED lighting from their different viewpoints. This expert feedback shows that “sustainable LED lighting” goes far beyond energy efficiency as it raises complex design issues that imply stakeholder negotiation. It also suggests that the LED paradox may be solved in context, but hardly in principle

Broadband emission from an ensemble of nano-pillars with multiple diameters

Conference 8641: Light-Emitting Diodes: Materials, Devices, and Applications for Solid State Lighting 17The Conference program's website is located at http://spie.org/x92791.xmlGenerating white light from monochromatic light sources is commonly achieved via one of two common methods: exciting fluorescence phosphors from a shorter wavelength LED, or mixing light from three or more LED chips, commonly known as RGB LEDs. Phosphor efficiency degrade over time, and have lifetimes shorter than the chip itself. RGB LEDs require turning on three or more p-n junctions and suffer from color mixing issues. We introduce a promising approach towards achieving phosphor-free white light emission, tapping on strain engineering and nanoscale processing. The proposed approach makes use of a long wavelength chip, which is …published_or_final_versio

High-sensitivity detection of narrowband light in a more intense broadband background using coherence interferogram phase

This paper describes an optical interferometric detection technique,. known as the interferogram phase step shift, which detects narrowband, coherent, and partially coherent light in more intense broadband incoherent background light using changes in the phase gradient with the optical path difference of the coherence interferograin to distinguish the bandwidth or coherence of the signal from that of the background. The detection sensitivity is assessed experimentally by measuring the smallest signal-to-background ratio or signal-to-clutter ratio (SCR), which causes a detectable change in the self-coherence interferograin phase. This minimum detectable SCR (MDSCR) is measured for the multimode He-Ne laser, resonant-cavity light-emitting diode (LED), narrowband-filtered white light, and LED signal sources in a more intense tungsten-halogen-lamp white-light background. The highest MDSCRs to date, to the authors' knowledge, are -46.42 dB for coherent light and -31.96 dB for partially coherent light, which exceed those of existing automatic single-domain techniques by 18.97 and 4.51 dB with system input dynamic ranges of 19.24 and 11.39 dB, respectively. The sensitivity dependence on the signal-to-system bandwidth ratio and on the relative offset of their central wavelengths is also assessed, and optimum values are identified

Standardization of a new photodiagnosis method based on LEDs for patients with solar urticaria sensitive to visible light

Standard methods for photodiagnosis of solar urticaria are based in exposure of patient skin to different polychromatic UV and visible sources where minimal urticarial doses for different spectral bands (UVB and UVA) are established. Classical photodiagnosis devices are based in solar simulation and use of UVB and UVA enhanced fluorescent lamps. In case of visible US photodiagnosis, US patient skin is exposed for 15 min to a slight projector, provided with halogen lamp, at a distance of 15 cms and presence of erythema and/or wheals is determined as positive reaction. Slights projector is from several years almost out of market due to use of new projection digital technologies and new visible light emerging technologies are good candidates for their substitution as photodiagnosis tool. The objective of the present work is to analyze photodiagnosis of visible light solar urticaria with using a LED device in comparison to normal slight projector exposure protocol. A total of twenty patients, from 7 different photodiagnosis units have participated in the study. Patients, with SU positive to visible light (with or without to UV radiation) following the standard photodiagnosis protocols were included in the study. Slight projector used in all photodiagnosis units were of similar characteristics and irradiance at 15 cm distance, as well as total dose of visible light after 15 min were calculated for each halogen lamp device. LED exposure was performed in parallel in a closed zone of the back of the patients. For LED photodiagnosis a prototype from University of Málaga (Spain) has been developed consisting in a black box provided with 4 holes of 12 mm diameter in which each hole white warm of a LED of 1 W is emitted. Thus, each LEDs dose is controlled independently and the device allows establishing, as well as for UVB and UVA normal protocols a MUD also under visible light. In that case, maximal visible light dose is reached in less than 5 min compared to 15 min under exposure to slight projector. All patients were positive to LED warm visible light with presence of erythema and / or wheals in parallel to the exposure to the slight projector. A MUD to visible light has been established with significant variations between patients which reveals different grade to visible light sensibilization. In conclusion, a new technology of illumination based in LEDs can be used in photodiagnosis of SU.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech