Lighting Research & Technology

This study set out to understand the benefits of improved illuminance uniformity in parking lots in terms of user perception and acceptability, as well as energy use, and to demonstrate that light-emitting diodes (LEDs) can achieve uniform distributions more efficiently than traditional light sources. The results from a field evaluation showed that more uniform illuminance distributions are favourably perceived by people in terms of goodness of illumination, ability to see around and at a distance, and perception of safety – all of this at a much lower average horizontal illuminance. Thus, improving uniformity alone can translate into lower energy use and potential for less glare and light pollution. Optical modelling showed that LEDs have a much greater potential to efficiently produce uniform illuminance distributions than larger light sources such as high pressure sodium or metal halide.

In this work, we propose an approach to estimating the amount of light wasted by being sent towards the upper hemisphere from urban areas. This is a source of light pollution. The approach is based on a predictive model that provides the fraction of light directed skywards in terms of a small set of identified explanatory variables that characterise the urban landscape and its light sources. The model, built via the statistical analysis of a wide sample of basic urban scenarios to compute accurately the amount of light wasted at each of them, establishes an optimal linear regression function that relates the fraction of wasted flux to relevant variables like the kind of luminaires, the street fill factor, the street width, the building and luminaire heights and the walls and pavement reflectances. We applied this model to evaluate the changes in emissions produced at two urban nuclei in the Deltebre municipality of Catalonia. The results agree reasonably well with those deduced from the radiance measurements made with the VIIRS instrument onboard the Suomi-NPP Earth orbiting satellite.

It is important to be able to engineer the brightness of interior spaces. In addition to the amount of light delivered to and reflected from surfaces in the space, light spectrum influences apparent scene brightness. Specifically, spaces illuminated by ‘cool white’ sources will look brighter than those illuminated by ‘warm white’ sources for the same photopic light levels. A scale model residential space was used to obtain judgements of scene brightness where light levels, surface reflectances and light source correlated colour temperatures were parametrically varied. Subjective and radiometric data were used to extend a provisional model of scene brightness, which is intended to be useful for predicting scene brightness of interior spaces illuminated to different levels by ‘white’ light sources of different correlated colour temperatures.

A digital circuit for driving a low-frequency, small-wattage, high-intensity discharge lamp is proposed. By combining a digital potentiometer X9313 and a microcontroller STM32F103, the lamp can be turned on and off automatically according to the operating condition. The lamp power can be altered flexibly based on the needed luminance because it is designed to be a linear function of the resistance of the potentiometer X9313. The lighting system has an electrical efficiency of 88% and can save more than 20% of energy, compared with a traditional lamp. A remote desktop client on Android is developed for the purpose of wireless and convenient control. The proposed model will provide important information for designing high-performance, low-frequency, small-wattage, high-intensity discharge lamps.

This paper studies spectrum optimization of four-package LEDs to improve performance of light sources with respect to properties such as luminous efficacy and colour rendering as well as luminous efficacy of radiation under photopic and mesopic conditions and circadian efficacy of radiation for non-visual biological effects. For colour mixing of four-package LEDs, the proportion of each LED in the package follows a linear relationship as does luminous efficacy. For optimization of luminous efficacy of radiation and circadian efficacy of radiation, an inverse proportion function model is proposed. An example of spectrum optimization for a four-package LED shows that by using the proposed model, high performance can be achieved with different weighting coefficients for different applications.

This paper describes two human factors experiments designed to assess the influence of flicker characteristics on the perception of stroboscopic effects from flickering light. Specifically, the following factors were investigated: temporal waveform shape, frequency, duty cycle, percent flicker and flicker index. For a given frequency, the flicker index appears to be more predictive of the detection and acceptability of stroboscopic effects than the percent flicker value.

This paper presents a systematic material selection process for technical, environmental and economic criteria. This methodology has been applied to the design of a weatherproof luminaire. The materials selected for the production of this diffuser were characterised to obtain their mechanical properties and to perform exhaustive research on impact analysis by means of finite element modelling. Also an economic analysis and an ecological impact assessment have been performed. Thanks to this working methodology, a final design of the diffuser has been developed having the optimum thickness to achieve the mechanical specifications and minimise the environmental impact and the cost of the diffuser.

In this paper, an LED downlight producing dynamic beam variation without any mechanically moving parts is presented. The functionality is based on an optics design using compound parabolic concentrators equipped with individual LEDs. With suitable driving of the LEDs, a dynamic far-field beam with an adjustment range of between 16° and 55° is achieved. The luminaire is used as a demonstration of the polyurethane vacuum casting rapid manufacturing method to produce low-cost freeform optics for prototypes. The simulations and measurements on the realized prototype show that the method is suitable for small series and prototype manufacturing, but also reveal potential errors in the rapid manufacturing process to be avoided in the future.

Using road lighting to improve the detection of potential hazards may contribute to reduced accident rates for pedestrians, drivers and other road users. In past studies carried out to measure peripheral detection, the test participant was instructed to maintain fixation on a target during presentation of the peripheral target, but these studies did not question the degree to which this fixation was maintained. We therefore used eye tracking to record fixations during a peripheral detection task and introduced a fixation task designed to encourage fixation. It was found that observers were good at maintaining foveal fixation and there was little benefit in introducing a fixation task although this might be of greater benefit if the peripheral field contains more interesting distractions.