Full Cutoff Research Articles

Qualifying lighting remodelling in a Hungarian city based on light pollution effects

The public lighting system has been remodelled in several Hungarian cities. In some cases the majority of the old luminaries were fitted with high pressure sodium lamps and they were replaced with white LED lighting with a typical correlated colour temperature of about 4500K. Therefore, these remodelling works provide a testbed for methods in measurements and modelling. We measured the luminance of the light domes of selected cities by DSLR photometry before and after the remodelling.Thanks to the full cut off design of the new lighting fixtures we obtained a slight decrease even in the blue part of the sky dome spectra of a tested city. However, we have to note that this positive change is the result of the bad geometry (large ULR) of the previous lighting system. Based on Monte Carlo radiative transfer calculations we provide a comparison of different indicators that can be used to qualify the remodelling, and to predict the possible changes in light pollution.

Relationship between the reflected brightness of artificial lighting and land-use types: a case study of the University of Arizona campus

Nighttime light pollution mars the view of the night sky, wastes energy, and adversely affects ecosystems and human health. In environmental design, efforts to reduce light pollution have often focused on the use of cutoff light fixtures to direct light toward the ground rather than skyward. The results of this study, however, indicate that light-fixture-oriented solutions are not a sufficient response to the problem. The study examined the relationship between nighttime light pollution and land-use types and found that some land-use types and their associated ground materials produce reflected light that contributes to light-pollution levels. As a first step to studying the relationship of land-use types to light pollution, a new method of acquiring high-resolution (sub-30-cm resolution) nighttime aerial images was developed to depict the reflected brightness of artificial lighting with a high degree of accuracy. Once the high-resolution imagery was acquired, 11 land-use types were delineated in the study area based on inspection of daytime aerial images and site visits. Finally, land uses and the nighttime image were compared, and an association between land-use types and nighttime light pollution levels was established. The general finding is that land-use types associated with highly reflective materials, such as concrete parking structures, reflect large amounts of light, producing light pollution even when full cutoff lights are used.

Unit Power Density Evaluations of Roadway Lighting Systems

In accordance with the ANSI/IESNA American National Standard Practice for Roadway Lighting, RP-8-00, roadway lighting calculations were made to investigate Unit Power Density (UPD). Calculations were made for specific luminaires, roadway configurations and lighting system geometries, over both a range of mounting heights (Ht) and a range of overhang-setback distances (Oh). For each value of Oh, at each Ht, the luminaire cycle distance was increased until any one of the illuminance or luminance criteria are not met. The last distance that meets all the criteria (for both the illuminance and luminance methods) is the maximum for that run. As the mounting height was increased over successive runs, maximum distance consistently increased, before decreasing. Overhang-setback was initially set at the midpoint of its range and at least five adjacent values calculated, then additional variations as necessary to determine the maximum spacing. Optimum luminaire cycle distance typically occurred when the combination with height and overhang result in the uniformity and average criteria both reaching their limits. Both high pressure sodium (HPS) and metal halide (MH) sources were included in the calculations, including some in each of the four classifications of cutoff, and applied to roads of varied classifications (local, collector and major) and widths from one to six lanes. Results indicate that roadway lighting systems which meet both the illuminance and luminance criteria, have predictably lower UPD values with HPS lamps than with MH lamps. The best MH systems have UPD values 1.5 to 1.8 times the values for the best HPS systems applied to similar roadways. Systems that meet only the Luminance method criteria have significantly lower UPD values than systems which meet the criteria for the Illuminance method or both methods. In addition, as luminaire cutoff becomes more stringent, a system's UPD value tends to increase. Systems designed to the Luminance method and with luminaires with HPS lamps and semi-cutoff or non-cutoff distributions typically produce the lowest UPD values for a given roadway classification and width, but as roadways become wider the differences decrease. The increase in UPD when full cutoff is required is shown to be from 9 percent to more than 20 percent.

A new mathematical model of the respiratory center.

A new mathematical model of the oscillatory behavior of the respiratory center has been developed based upon published records of neuronal activity during respiration in the pons and medulla. In contrast with a previous model, four, rather than two, networks are assumed to interact in the respiratory center so as to produce the respiratory oscillation. A mathematical description of this interaction, in the form of a set of four first-order, nonlinear, coupled differential equations, is derived; the behavior of the solutions of this system is studied qualitatively, and expressions for the durations of the inspiratory and expiratory phases are obtained in terms of some parameters. It is found that central and chemical influences drive the medullar neurons to a position somewhere between saturation and full cutoff, and the pontine neurons deeply into cutoff. The control of the duration of the different phases by these chemical and central means is discussed. In order to effect a decrease in the magnitude of the various times, the neurons have to be driven towards operating points of higher central facilitation.