Low Pressure Sodium Research Articles

Exploring the Hidden World of Lighting Flicker with a High-Speed Camera

Alternating current can result in flickering—or pulsing—in the brightness of light emitted by luminaires. Lighting flicker typically occurs in the range of 100 to 140 cycles per second (Hz), which is too fast for visual perception by most organisms. However, evidence indicates that many organisms perceive flicker with non-visual photoreceptors present on the retinas. Exposure to flickering lights at night disrupts the circadian rhythm of organisms, leading to symptoms similar to blue light exposure at night. The traditional method for detecting flickering is with a flickermeter held near a single light. In this paper, we explore the use of high-speed camera data in the collection of temporal profiles for groups of luminaires simultaneously at distances ranging from several meters to several kilometers. Temporal profiles are extracted for individual lighting features and the full scene. The identification of luminaire types is based on their spectral signatures. With the camera data, it is possible to identify flickering and non-flickering lights, to determine the flicker frequency, to calculate percent flicker and the flicker index, and to identify groups of lights whose flickers are synchronized. Both flickering and non-flickering luminaires can be found for LED, metal halide, fluorescent, and compact fluorescent lights. To date, flickering has been detected in all of the incandescent, high-pressure sodium, and low-pressure sodium luminaires that we measured. We found that flicker synchronization is often present for lights installed within a single facility and also for strings of streetlights. We also found that flicker exposure can come from the light reflected off of the earth’s surface. Luminaires designed to illuminate large areas often saturate high-speed camera data collection. This saturation can be reduced or eliminated using neutral density filters on the camera. Published experimental data on the impacts of flicker on organisms remains sparse. Many studies have drawn inferences on the impacts of spectral and lighting brightness on organisms without controlling for flicker. Our conclusion is that lighting flicker is a type of light pollution. The use of high-speed camera data makes it easier to include flicker as a variable in studies regarding the impacts of lighting on organisms.

Mitigating urban light pollution: A review of municipal regulations and implications for planners

ABSTRACT Propelled by more energy-efficient technologies such as light-emitting diodes, the growth of outdoor light at night is raising concerns about light pollution (LP). Given mounting evidence of LP’s risks to human wellbeing, nature and wildlife, and views of the dark sky, this paper examines the extent to which LP concerns are addressed in land use plans, policies, and regulations in nine U.S. cities, including Flagstaff, Arizona, a city known for its model lighting code. Through a review of zoning and other ordinances, area and sectoral plans and policies, media reports, and interviews with planners, this study documents that LP has yet to be taken seriously in municipal codes of most study cities. Drawing from the Flagstaff model, it offers recommendations for evidence-based, objective standards for three key dimensions of LP-mitigation: limiting total illumination or lumens per acre, shielding of lamps, and specifying luminaire characteristics. ABBREVIATIONS AMA: American Medical Association; APA: American Planning Association; CCT: Correlated Color Temperature; CRI: Color Rendition Index; ESCO: Energy Service Companies; f.c.: foot candle; HPS: High-Pressure Sodium; IDA: International Dark-Sky Association; LED: Light-Emitting Diode; LP: Light Pollution; LPS: Low-Pressure Sodium; LZ: Lighting Zone; NSA: Narrow-Spectrum Amber

EFICIÊNCIA ENERGÉTICA EM ILUMINAÇÃO PÚBLICA: ESTUDO DE CASO DO BAIRRO JARDIM SANTA FÉ

Currently, energy efficiency is considered one of the main areas of investment, both by governments and organizations, as its implementation leads to a reduction in energy consumption and consequently reduces dependence on external energy sources, which has a positive impact on economic competitiveness and social development. Within this context, public lighting becomes relevant, as it has great potential in terms of its ability to reduce consumption, largely due to the outdated systems that are still common in public thoroughfares. Thus, aiming to implement a new system through a direct replacement of lighting equipment in the Santa Fé neighborhood, in Dourados-MS, a case study was conducted to assess the financial feasibility of this project, by directly replacing low-pressure sodium vapor lamps with modern LED lamps and subsequently conducting a financial analysis using the indicators NPV, IRR, and Payback. The analysis of the expected cash flow for the acquisition of the luminaires presented positive results and indicated that the lighting system upgrade is a profitable investment. With an investment value of R$136,300.73, the net present value was R$61,245.63. Additionally, the expected internal rate of return for the investment was 22%, indicating a good return on investment. The Payback, which is the period required to recoup the investment, was estimated at 6.93 years. Based on these results, it is observed that the investment is viable and can bring considerable financial benefits.

First Nighttime Light Spectra by Satellite—By EnMAP

For the first time, nighttime VIS/NIR—SWIR (visible and near-infrared—shortwave infrared) spectra from a satellite mission have been analyzed using the EnMAP (Environmental Mapping and Analysis Program) high-resolution imaging spectrometer. This article focuses on the spectral characteristics. Firstly, we checked the spectral calibration of EnMAP using sodium light emissions. Here, By applying a newly devised general method, we estimated shifts of +0.3nm for VIS/NIR and −0.2nm for SWIR; the uncertainties were found to be within the range of [−0.4nm,+0.2nm] for VIS/NIR and [−1.2nm,+1.0nm] for SWIR. These results emphasize the high accuracy of the spectral calibration of EnMAP and illustrate the feasibility of methods based on nighttime Earth observations for the spectral calibration of future nighttime satellite missions. Secondly, by employing a straightforward general method, we identified the dominant lighting types and thermal emissions in Las Vegas, Nevada, USA, on a per-pixel basis, and we considered the consistency of the outcomes. The identification and mapping of different types of LED (light-emitting diode) illuminations were achieved—with 75% of the identified dominant lighting types identified in VIS/NIR—as well as high- and low-pressure sodium and metal halide, which made up 22% of the identified dominant lighting types in VIS/NIR and 29% in SWIR and other illumination sources, as well as high temperatures, where 33% of the identified dominant emission types in SWIR were achieved from space using EnMAP due to the elevated illumination levels in the observed location. These results illustrate the feasibility of the precise identification of lighting types and thermal emissions based on nighttime high-resolution imaging spectroscopy satellite products; moreover, they support the specification of spectral characteristics for upcoming nighttime missions.

Long-term effects of artificial nighttime lighting and trophic complexity on plant biomass and foliar carbon and nitrogen in a grassland community.

The introduction of artificial nighttime lighting due to human settlements and transport networks is increasingly altering the timing, intensity, and spectra of natural light regimes worldwide. Much of the research on the impacts of nighttime light pollution on organisms has focused on animal species. Little is known about the impacts of daylength extension due to outdoor lighting technologies on wild plant communities, despite the fact that plant growth and development are under photoperiodic control. In a five‐year field experiment, artificial ecosystems (“mesocosms”) of grassland communities both alone or in combination with invertebrate herbivores and predators were exposed to light treatments that simulated street lighting technologies (low‐pressure sodium, and light‐emitting diode [LED]‐based white lighting), at ground‐level illuminance. Most of the plant species in the mesocosms did not exhibit changes in biomass accumulation after 5 years of exposure to the light treatments. However, the white LED treatment had a significant negative effect on biomass production in the herbaceous species Lotus pedunculatus. Likewise, the interaction between the white LED treatment and the presence of herbivores significantly reduced the mean shoot/root ratio of the grass species Holcus lanatus. Artificial nighttime lighting had no effect on the foliar carbon or nitrogen in most of the grassland species. Nevertheless, the white LED treatment significantly increased the leaf nitrogen content in Lotus corniculatus in the presence of herbivores. Long‐term exposure to artificial light at night had no general effects on plant biomass responses in experimental grassland communities. However, species‐specific and negative effects of cool white LED lighting at ground‐level illuminance on biomass production and allocation in mixed plant communities are suggested by our findings. Further studies on the impacts of light pollution on biomass accumulation in plant communities are required as these effects could be mediated by different factors, including herbivory, competition, and soil nutrient availability.

High Pressure Sulfur Microwave Lamps with Metal Halides Additives

Effects of metal halides additives on radiation characteristics of microwave-driven high pressure sulphur lamp were experimentally studied. Electrodeless discharge was excited and maintained in the mixture of sulphur vapour (5–6) atmospheres and vapour of NaI (~ 0.07 Torr) and LiI (~ 0.12 Torr) at microwave frequency of 2.45 GHz and power of (280–560) W in the quartz spherical bulb of 35 mm in diameter inserted in the cylindrical resonator of 73 mm in diameter and 125 mm in height. To maintain bulb walls at homogeneous temperature, the bulb was rotated with the speed of the 12 r/c. It was found that the addition of low pressure sodium and lithium halides caused the increase of lamp efficacy by (11–13) %, colour temperature by 16 %, and colour rendering index by 4 %. To further improve lamp characteristics, the increase of additives partial pressures was recommended.

Effects of UV–visible radiation on growth, photosynthesis, pigment accumulation and UV-absorbing compounds in the red macroalga Gracilaria cornea (Gracilariales, Rhodophyta)

Radiation induces different processes in photosynthetic organisms through photosynthetic pigments and photoreceptors. This study evaluated the performance of the red alga Gracilaria cornea cultivated under different radiation treatments. The objective was to identify responses associated with the treatments and mediated by photoreceptors. For this, G. cornea was exposed for 15 days to low fluence radiation of the ultraviolet (UV)-visible spectrum (red, green and blue light, and UV-A and UV-B radiation) combined with a high fluence radiation provided by a low-pressure sodium lamp (SOX), in order to saturate the photosynthesis. We measure the growth rate and other variables, such as photosynthesis estimated as chlorophyll a fluorescence, chlorophyll a, phycobiliproteins, carotenoids, mycosporine-like amino acids (MAAs), phenolic compounds, antioxidant capacity soluble proteins, and internal carbon and nitrogen content. The results showed that the UV radiation influenced the growth rates, as well as the accumulation of internal compounds (carotenoids: violaxanthin, antheraxanthin and zeaxanthin; MAA palythine; and phenolic compounds). As the treatments with UV radiation also had a peak of blue light, the presence of photoreceptors sensitive to these qualities of radiation (UV-A, UV-B and blue light) is suggested. In general, UV-A appears to induce some compounds without affecting growth, while UV-B seems to cause the accumulation of compounds at the expense of growth. The effect of light quality on growth and metabolism in G. cornea is compared to that in other species following similar experimental design.

The VIIRS Day/Night Band: A Flicker Meter in Space?

The VIIRS day/night band (DNB) high gain stage (HGS) pixel effective dwell time is in the range of 2–3 milliseconds (ms), which is about one third of the flicker cycle present in lighting powered by alternating current. Thus, if flicker is present, it induces random fluctuations in nightly DNB radiances. This results in increased variance in DNB temporal profiles. A survey of flicker characteristics conducted with high-speed camera data collected on a wide range of individual luminaires found that the flicker is most pronounced in high-intensity discharge (HID) lamps, such as high- and low-pressure sodium and metal halides. Flicker is muted, but detectable, in incandescent luminaires. Modern light-emitting diodes (LEDs) and fluorescent lights are often nearly flicker-free, thanks to high-quality voltage smoothing. DNB pixel footprints are about half a square kilometer and can contain vast numbers of individual luminaires, some of which flicker, while others do not. If many of the flickering lights are drawing from a common AC supplier, the flicker can be synchronized and leave an imprint on the DNB temporal profile. In contrast, multiple power supplies will throw the flickering out of synchronization, resulting in a cacophony with less radiance fluctuation. The examination of DNB temporal profiles for locations before and after the conversion of high-intensity discharge (HID) to LED streetlight conversions shows a reduction in the index of dispersion, calculated by dividing the annual variance by the mean. There are a number of variables that contribute to radiance variations in the VIIRS DNB, including the view angle, cloud optical thickness, atmospheric variability, snow cover, lunar illuminance, and the compilation of temporal profiles using pixels whose footprints are not perfectly aligned. It makes sense to adjust the DNB radiance for as many of these extraneous effects as possible. However, none of these adjustments will reduce the radiance instability introduced by flicker. Because flicker is known to affect organisms, including humans, the development of methods to detect and rate the strength of flickering from space will open up new areas of research on the biologic impacts of artificial lighting. Over time, there is a trend towards the reduction of flicker in outdoor lighting through the replacement of HID with low-flicker LED sources. This study indicates that the effects of LED conversions on the brightness and steadiness of outdoor lighting can be analyzed with VIIRS DNB temporal profiles.

LUMINESCENT COATINGS BASED ON PR-CONTAINING COMPLEX OXIDES FOR THE ELABORATION OF PHYTO-LEDS

Plants in greenhouses are grown under special lighting conditions, i.e. when partially or completely artificial lighting is used. For this purpose, various lamps are used - xenon, high or low pressure sodium, mercury, LED, etc. Recent studies have shown that LED lamps can achieve about 60 % more efficiency in greenhouse lighting than sodium lamps. The increased energy efficiency of LED lamps (phyto-lamps) is associated with the coincidence of their emission bands with the spectra of photosynthetic active radiation. The simplest phyto-lamps are devices consisting of several blue and red light LEDs (phyto-LEDs). A significant disadvantage of red LEDs those are based on the semiconductor structures is their cost, which is much higher than that of blue phyto-LEDs. One of the ways to reduce the price of red LEDs can be their elaboration on the basis of an InGaN semiconductor structure (chip) with a blue light emission, with a deposited layer of an inorganic phosphor. Phosphors with a red emission can be created on the basis of oxide materials with ions of transition or rare earth metals, such as Pr3+. The advantage of praseodymium over transition element ions is that the main absorption bands of Pr3+ ions in the visible region located in the range of 430–490 nm, namely in the emission region of blue LEDs. The position of these bands weakly depends on the type of crystalline or glass matrix. In this work, luminescent coatings based on KBi(MoO4)2 and K2Bi(PO4)(MoO4) crystals doped with Pr3+ ions are considered. The coating on the LED was carried out using a polymer - cyanoacrylate glue. It has been found that the polymer used weakly absorbs LED radiation and does not exhibit significant luminescence in the visible region upon excitation at 446 nm. For a coating based on K2Bi0.99Pr0.01(PO4)(MoO4), it was shown that, in terms of the position of the oxide luminescence bands, it agrees well with the red absorption band of chlorophyll b and with weak absorption bands of chlorophyll in the range of 590–620 nm. However, the efficiency of blue into red light converting for this coating is rather low. Better results can be achieved with KBi0.9Pr0.1(MoO4)2, which has a better correlation with chlorophyll’s absorption bands, as well as a higher blue-to-red conversion efficiency. In our opinion, by varying the content of praseodymium in KBi1-xPrx(MoO4)2 and optimizing the deposition method, it is possible to increase the efficiency of such luminescent coatings for the development of phyto-LEDs.

Energy­Saving Lighting of Agricultural Premises and its Parameters Calculation

he properly selected lighting for livestock farms is noted to ensure the optimal productivity of bred animals and poultry and to generate profit for the enterprise. (Research purpose) The research purpose is to substantiate the parameters of energy-saving lighting for agricultural premises and to develop methods for its calculation. (Materials and methods) It has been shown that greenhouse farms most often use high and low pressure sodium lamps for lighting, but their spectrum only partially substitutes the natural one. It has been assumed that expanding the spectrum and approximating it to the solar one could improve product quality and yield. It has been stated that incandescent and fluorescent lamps are traditionally used to illuminate livestock and poultry premises, but they cannot create a lighting system with a «dawn - sunset» function, and their spectrum does not correspond to the full range perceived by animals and birds. It has been noted that the LED light sources’ functioning has such features that make the application of standard calculation methods impossible. We obtained formulas for calculating the light level and flux of photons. (Results and discussion) We provided examples of applying the energy-saving lighting systems developed by us in poultry houses with floor housing system, in cowsheds with tethered housing system and in an experimental phyto-laboratory for growing seedlings. It has been found that after replacing the lighting system based on DRL-125 lamps with a new one, with 36 nine-watt LED lamps, the power consumption decreased from 2,250 to 336 watts, the average light level increased and amounted to 90 lux, while the illumination uniformity and color rendition improved. We have developed a resonant power supply system for LEDs to create lighting systems with a «sunrise - sunset» function. (Conclusions) We have shown the possibility and provided examples of using the developed by us energy-saving controlled lighting systems based on LED light sources.

Photobiological Effects on Biochemical Composition in Porphyridium cruentum (Rhodophyta) with a Biotechnological Application.

This study describes the relation of photosynthetic capacity, growth and biochemical compounds in the microalgae Porphyridium cruentum under saturated irradiance (200μmolm-2 s-1 ) by white light (WL) and low-pressure sodium vapor lamps (SOX lamps-control) and supplemented by fluorescent lamps (FLs) with different light qualities (blue: λmax = 440nm; green: λmax = 560nm; and red: λmax = 660nm). The maximum photosynthetic efficiency (Fv / Fm ) showed a positive correlation with the light quality by saturating light SOX in mixture with stimulating blue light than the white light (WL) at the harvest day (10days). The production, that is maximal electron transport rate (ETRmax ), and energy dissipation, that is maximal nonphotochemical quenching (NPQmax ), had the same pattern throughout the time (3-6days) being the values higher under white light (WL) compared with SOX and SOX plus supplemented different light qualities. Total protein levels increased significantly in the presence of SOX light, while phycoerythrin (B-PE) showed significant differences under SOX+ blue light. Arachidonic acid (ARA) was higher under SOX and SOX plus supplemented different light qualities than that under WL, whereas eicosapentaenoic acid (EPA) was the reverse. The high photomorphogenic potential by SOX light shows promising application for microalgal biotechnology.

S-CLC Compensated Wireless Power Transfer With Pulse-Frequency-Modulation Control for Dimmable Low-Pressure Sodium Lamps

This article proposes and implements a wireless power transfer (WPT) with series-capacitor-inductor-capacitor (S-CLC) compensation network and pulse-frequency-modulation (PFM) control for dimmable low-pressure sodium (LPS) lamps. Considering the high-voltage ignition and long-time operation, the LPS lamp has the risk of causing electrocution, especially when operating in a humid environment. Thus, the wireless lighting is highly desirable since the LPS lamp can be completely isolated with maintenance-free under all-weather conditions. The proposed S-CLC compensation for WPT can directly drive the LPS lamp without utilizing any magnetic or electronic ballasts. In addition, the PFM control can achieve effective dimming control, reduced operating frequency, and zero-voltage switching (ZVS) concurrently. Theoretical calculations and experimental results are given to validate the feasibility of the proposed wireless lighting system.

Light quality triggers biochemical modulation of Cyanobium sp.—photobiology as tool for biotechnological optimization

Cyanobacteria are able to absorb light over a wide spectral range due to the presence of photoreceptors, making it possible to modulate the production of high-value compounds by inducing specific pathways. In order to evaluate the influence of light quality in cyanobacteria metabolism, Cyanobium sp. was grown in five different light conditions, by using low-pressure sodium vapor lamp (SOX) supplemented with low irradiances of green, red, and blue light and UV radiation compared to a control with only SOX. The effects of light supplementation on biomass productivity, photosynthetic activity, biochemical composition, and total antioxidant capacity were evaluated. No changes in biomass productivity were induced by any light supplements. The supplementation of red light triggered the production of lipids, phycocyanin, carotenoids, and total antioxidant compounds, while supplementation of green light increased the content of carbohydrates and chlorophyll a. Thus, supplementation of blue light and UV radiation showed little or no improvements to the culture, whereas under UV radiation the photosynthetic activity was reduced. Overall, Cyanobium sp. is a promising strain, mainly due to its accessibility to metabolism photoregulation as to produce various bioactive compounds.

Light regulating metabolic responses of Cyanobium sp. (Cyanobacteria)

Cyanobacteria are an important group of microorganisms of significant economic interest due to, for ex-ample, the antioxidant capacity of their metabolites. Cyanobium sp. LEGE 06113 is a marine cyanobacterium poorly studied, but with promising future applications. The aim of this study was to optimize the light conditions (both source and irradiance) and nutrient (N and P) concentration for Cyanobium sp. production as a source of high-valued com-pounds. The optimization of the processing parameters was performed using two different light sources (fluorescent and low-pressure sodium lamp), four irradiances (50, 100, 200 and 300 µmol photons m– 2 s–1) and two variations of BG11 medium (BG11 and BG11+, with the second containing double amounts of phosphates and nitrates). The effects of the three factors were evaluated on the biomass production, photosynthetic activity, biochemical composition and antioxidant capacity. A synergistic effect between the light source, light intensity, and medium was observed for all measured parameters, with the greatest impact of light irradiance on the metabolism of Cyanobium sp. The combination of the SOX lamp, BG11+ medium, and a light irradiance of 200 µmol photons m– 2 s–1 was optimal for the cultivation of Cyanobium sp. This work reports the tools for the production of Cyanobium sp. as a source of high-value products, thus increasing its biotechnological potentials.

Switching LPS to LED Streetlight May Dramatically Reduce Activity and Foraging of Bats

Artificial light at night is considered a major threat to biodiversity, especially for nocturnal species, as it reduces habitat availability, quality, and functionality. Since the recent evolution in light technologies in improving luminous efficacy, developed countries are experiencing a renewal of their lighting equipment that reaches its end-of-life, from conventional lighting technologies to light emitting diodes (LEDs). Despite potential cascading impacts of such a shift on nocturnal fauna, few studies have so far dealt with the impact of the renewal of street lighting by new technologies. Specifically, only one study, by Rowse et al.2016, examined the effects of switching from widely used low pressure sodium (LPS) lamps to LEDs, using bats as biological models. This study was based on a before-after-control-impact paired design (BACIP) at 12 pairs in the UK, each including one control and one experimental streetlight. If Rowse et al. 2016 showed no effect of switching to LEDs streetlights on bat activity, the effects of respective changes in light intensity and spectrum were not disentangled when testing switch effects. Here, we conduct a retrospective analysis of their data to include these covariates in statistical models with the aim of disentangling the relative effects of these light characteristics. Our re-analysis clearly indicates that the switches in spectrum and in intensity with replacement of LPS with LED lamps have significant additive and interactive effects, on bat activity. We also show that bat activity and buzz ratio decrease with increasing LED intensity while an opposite effect is observed with LPS lamps. Hence, the loss or the gain in bat activity when lamp types, i.e., spectrum, are switched strongly depends on the initial and new lamp intensities. Our results stress the need to consider simultaneously the effects of changes in the different lights characteristics when street lighting changes. Because switches from LPS to LED lamps can lead to an increase in light intensity, such technological changes may involve a reduction of bat activity in numerous cases, especially at high LED intensities. Since we are currently at an important crossroad in lighting management, we recommend to limit LED intensity and improve its spectral composition toward warmer colors to limit potential deleterious impacts on bat activity.

Spectral study of Na source with a smartphone and a diffraction grating

A home-made spectrometer, based on the use of inexpensive diffraction transmission gratings coupled with a smartphone camera, can be assembled and employed to obtain quantitative spectra of different sources with surprisingly high accuracy to the point of being able to observe the separation of the Na-doublet (the wavelength difference between the two emission D-lines of the sodium spectrum).We describe the set up and data analysis required to acquire the emission spectra of a low-pressure sodium discharge lamp and perform such measurement. The experiment addresses a relevant and engaging topic in physics, namely optical spectroscopy, and is suitable for the undergraduate laboratory and for working with high school students.

Paradoxical impact of memory on color appearance of faces

What is color vision for? Here we compared the extent to which memory modulates color appearance of objects and faces. Participants matched the colors of stimuli illuminated by low-pressure sodium light, which renders scenes monochromatic. Matches for fruit were not predicted by stimulus identity. In contrast, matches for faces were predictable, but surprising: faces appeared green and looked sick. The paradoxical face-color percept could be explained by a Bayesian observer model constrained by efficient coding. The color-matching data suggest that the face-color prior is established by visual signals arising from the recently evolved L-M cone system, not the older S-cone channel. Taken together, the results show that when retinal mechanisms of color vision are impaired, the impact of memory on color perception is greatest for face color, supporting the idea that trichromatic color plays an important role in social communication.

Effects of Sodium Lighting On Circadian Rhythms in Rats.

Rodent studies often must be conducted during an animal's active phase (that is, in darkness) yet also during a typical day shift for staff. Low-pressure sodium lighting (LPSL), to which human retinas are more sensitive than rodents' at low intensity, has been used to facilitate study conduct in dark phase. The assumption was that LPSL would be equivalent to total darkness due to low rodent retinal sensitivity but provide enough lighting for safe technical manipulations due to higher human retinal sensitivity. Unlike other light sources, LPSL has been tested for effects on circadian rhythm specific to locomotive activities in albino mice. Whether LPSL affects circadian rhythms in rats is unknown. In this study, circadian endpoints were derived from body temperature and locomotor activity via telemeters in 8 adult male Wistar rats. When moved from a 12:12-h white-light (that is, cold white fluorescent light):dark (LD) cycle to a 12:12-h white-light:sodium-light cycle, rats demonstrated free-running and disrupted circadian rhythms (that is, lengthened circadian period and reduced circadian robustness and amplitude). Body temperature and locomotor activity were significantly lower in the LPSL phase as compared with dark phase under the baseline condition. When exposed to a 12:12 h sodium-light:dark (SD) cycle, rats entrained with a circadian period similar to 12:12-h white-light:dark (LD), but significantly different from the period under constant darkness (DD). Circadian onset and acrophase were delayed under SD compared with LD. When illuminated with a LPSL pulse under DD, rats showed phase shifts similar to white-light pulse effects, consistent with the phase response curve. To determine whether the image-forming photoreceptors are involved in this process, we used electroretinography. Compared with white light, 589-nm light generated during electroretinography elicited rod photoreceptors responses with longer latency and cone photoreceptor responses with lower amplitude. These results indicate that LPSL is a weaker zeitgeber than white light and may alter the circadian system in rats. Furthermore, because LPSL appeared to be visible to rats, it may not be an appropriate substitute for actual darkness.

Optimizing Lighting of Rural Roads and Protected Areas with White Light: A Compromise among Light Pollution, Energy Savings, and Visibility

ABSTRACTThe broad implementation of light emitting diode (LED) light sources in public lighting has become a revolution in recent years. Their low power consumption and good performance (extremely low onset time, long lifetime, high efficacy) make LEDs an optimal solution in most outdoor applications. In addition, the white light emitted by the vast majority of LEDs used in public lighting and their good color rendering improve well-being, comfort, and safety in cities, especially in commercial zones and urban centers. However, regulations on light pollution that have been developed in some countries in parallel to the introduction of LED lighting impose strong constraints to white light emission, which is present due to the higher Rayleigh scattering of short wavelengths. These regulations request filtering blue wavelengths in some protected areas and thus limit the projects to high- or low-pressure sodium sources or amber LEDs. In this work, the pros and cons of white and amber LED lighting in rural areas are analyzed and compared through simulations made on a typical rural lighting situation and considerations based on efficiency, visual performance, nonvisual effects, and light pollution. The most important conclusion is that Rayleigh scattering seems to prevail in the current considerations on light pollution, whereas other important aspects affecting safety and sustainability are are not considered. Accurate designs can decrease light pollution without constraints against white LEDs. The objective of this work is to provide evidence leading to consider light pollution from a more general perspective in the benefit of humans and the environment.

Blood Pressure in relation to 24-Hour Urinary Sodium and Potassium Excretion in a Uruguayan Population Sample.

Many public health policies in Latin America target an optimized sodium and potassium intake. The aims of this study were to assess the sodium and potassium intake using 24-hour urinary analysis and to study their association with blood pressure in a Uruguayan population cohort using cluster analysis. A total of 149 participants (aged 20–85 years) were included in the study, and office blood pressure, anthropometric measurements, biochemical parameters in the blood, and 24-hour urine samples were obtained. The overall mean sodium and potassium excretion was 152.9 ± 57.3 mmol/day (8.9 ± 3.4 g/day of salt) and 55.4 ± 19.6 mmol/day, respectively. The average office systolic/diastolic blood pressure was 124.6 ± 16.7/79.3 ± 9.9 mmHg. Three compact spherical clusters were defined in untreated participants based on predetermined attributes, including blood pressure, age, and sodium and potassium excretion. The major characteristics of the three clusters were (1) high systolic blood pressure and moderate sodium excretion, (2) moderate systolic blood pressure and very high sodium excretion, and (3) low systolic blood pressure and low sodium excretion. Participants in cluster three had systolic blood pressure values that were 23.9 mmHg (95% confidence interval: −29.5 to −1.84) lower than those in cluster one. Participants in cluster two had blood pressure levels similar to those in cluster one (P = 0.32) and worse metabolic profiles than those in cluster one and three (P < 0.05). None of the clusters showed high blood pressure levels and high sodium excretion. No linear association was found between blood pressure and urinary sodium excretion (r < 0.14; P > 0.47). An effect of sodium and potassium intake on blood pressure levels was not found at the population level using regression or cluster analysis.