Showing papers in "Lighting Research & Technology in 2013"

Comparisons of three practical field devices used to measure personal light exposures and activity levels

Abstract: This paper documents the spectral and spatial performance characteristics of two new versions of the Daysimeter, devices developed and calibrated by the Lighting Research Center to measure and record personal circadian light exposure and activity levels, and compares them to those of the Actiwatch Spectrum (Philips Healthcare). Photometric errors from the Daysimeters and the Actiwatch Spectrum were also determined for various types of light sources. The Daysimeters had better photometric performance than the Actiwatch Spectrum. To assess differences associated with measuring light and activity levels at different locations on the body, older adults wore four Daysimeters and an Actiwatch Spectrum for five consecutive days. Wearing the Daysimeter or Actiwatch Spectrum on the wrist compromises accurate light measurements relative to locating a calibrated photosensor at the plane of the cornea.

Lighting affects students’ concentration positively: findings from three Dutch studies

Abstract: The importance of lighting for performance in human adults is well established. However, evidence on the extent to which lighting affects the school performance of young children is sparse. This paper evaluates the effect of lighting conditions (with vertical illuminances between 350 lux and 1000 lux and correlated colour temperatures between 3000 and 12 000 K) on the concentration of elementary school children in three experiments. In the first two experiments, a flexible and dynamic lighting system is used in quasi-experimental field studies using data from 89 pupils from two schools (Study 1) and 37 pupils from two classrooms (Study 2). The third experiment evaluated two lighting settings within a school-simulating, windowless laboratory setting (n = 55). The results indicate a positive influence of the lighting system on pupils’ concentration. The findings underline the importance of lighting for learning. Several suggestions are made for further research.

CRI2012: A proposal for updating the CIE colour rendering index

Abstract: The CIE colour rendering index (CRI) has been criticized for its poor correlation with the visual colour rendering of many spiked or narrowband sources, its outdated colour space and chromatic adaptation transform and the use of a small number of non-optimal reflectance samples that have enabled lamp manufacturers to tune the spectrum of a light source to yield, in some cases, inappropriately high general CRI values. The CRI2012 metric proposed in this paper addresses these criticisms by combining the most state of the art colorimetric colour difference model, i.e. CAM02-UCS, with a mathematical reflectance set that exhibits a highly uniform spectral sensitivity. A set of 210 real reflectance samples has also been selected to provide additional information on the expected colour shifts when changing illumination.

Discomfort Glare: What Do We Actually Know?

Abstract: Glare models were reviewed with an eye for missing conditions or inconsistencies. Ambiguities were found relating to when to use small source versus large source models and as to what constitutes a...

A new direction for general lighting practice

Abstract: The currently accepted notion that the basic purpose of general lighting practice is to enable performance of visual tasks is examined and found to be lacking in substance. It is proposed that the ...

User preferences for LED lighting in terms of light spectrum

Abstract: A study was carried out in light booths to investigate user preference for different light spectra. Twenty-one LED spectra and three fluorescent lamps, all at three different correlated colour temperatures were used for the study. Sixty observers evaluated the lit scenes under different spectra for naturalness of selected objects, colourfulness of a Macbeth Colour Checker Chart, and the visual conditions of the lighting booths. The observers preferred the spectral power distributions (SPD) under which the chroma and colourfulness values of the object colours were higher. The CIE Colour Rendering Index was not a good indicator of the observers’ preference for the LED SPDs. It seemed that light sources with a higher CQS Gamut Area Scale and CQS Colour Preference Scale values were preferred by the observers as far as LED spectra were concerned. However, the CQS Gamut Area Scale calculated with a new version of the software (version 9.2) and the Gamut Area Index were suitable as indicators of observers’ prefe...

Dynamic control of supplemental lighting intensity in a greenhouse environment

Abstract: The global increase in energy prices, the urgent need to reduce CO2 emissions to the atmosphere and the high energy usage are currently the major threats to the greenhouse industry. Optimised contr...

Flicker can be perceived during saccades at frequencies in excess of 1 kHz

Abstract: When driving at night, flickering automobile LED tail lights can appear as multiple images. The perception of a flickering source of light was therefore studied during rapid eye movements (saccades...

LED street lighting: A power quality comparison among street light technologies

Abstract: High-pressure sodium lamps are currently the main lamps used in public lighting. However, the possibility of using high-power light emitting diode (LEDs) for street lighting is growing continuously due to their greater energy efficiency, robustness, long life and light control. The aim of this paper is to study the power quality of high-power lighting networks based on LED and high-pressure sodium lamps. Both electromagnetic and dimmable electronic ballasts, which can dim the lamp output smoothly and uniformly, have been used connected to high-pressure sodium lamps. High-pressure sodium lamps connected to electronic equipment have been tested with different arc power levels using dimming on a 230 V power supply. The study presented in this paper is completely based on measurements, including harmonic currents in the frequency range up to 150 kHz for all the technologies. The main results show a broadband spectrum in LED lamps which confirms other research in fluorescent lamps powered by high-frequency ball...

Investigation of Evalglare software, daylight glare probability and high dynamic range imaging for daylight glare analysis

Abstract: The latest glare metric, called daylight glare probability (DGP), has been developed specifically for daylight glare issues inside a building. Unlike other glare indices, DGP considers vertical ill...

Using obstacle detection to identify appropriate illuminances for lighting in residential roads

Abstract: This paper uses data regarding detection of pavement obstacles to explore two approaches to establishing an appropriate illuminance for road lighting designed to meet the needs of pedestrians. A previous obstacle detection experiment was repeated using young observers under high pressure sodium (HPS) lighting. One approach was to identify whether there is a plateau-escarpment relationship between obstacle detection ability and illuminance – better detection with increasing light level until further increases bring little improvement: This suggested an appropriate illuminance of 5.7 lux. The second approach was to identify the size of an obstacle that a pedestrian should expect to be able to detect and the associated probability of detection: An obstacle of height 25 mm located 6 m ahead may require 1.8 lux to be detected with 95% probability.

Subjective preferences and colour quality metrics of LED light sources

Abstract: To understand people's judgement of the naturalness of object colours and preference for the lit environment, lighting booth experiments were conducted. Seven different LED spectral power distribut...

Daylight utilisation in perimeter office rooms at high latitudes: Investigation by computer simulation

Abstract: A simulation study of daylight autonomy in perimeter office rooms at high latitudes is presented where the following variables are studied: Glazing-to-wall ratios (GWR), climate, orientation, inner surface reflectance, glazing visual transmittance, Venetian blind management and electric lighting dimming and switching systems. Based on daylight utilisation alone, the results indicate an optimal GWR ranging between 20% and 40%, with a North orientation requiring a larger GWR (40%), a South orientation a smaller GWR (20%) and an East/West orientation an intermediate GWR (30%). The reflectance of inner surfaces has a significant effect on daylight autonomy and the use of low transmittance glazing demands a larger GWR (60%) to achieve the same daylight autonomy as 20% GWR with high transmittance glazing. Also, the results indicate that the choice of electric lighting dimming and switching systems has a more significant impact on electricity use than the GWR, orientation and the other variables examined.

High dynamic range photogrammetry for synchronous luminance and geometry measurement

Abstract: This study developed high dynamic range photogrammetry for synchronous acquisition of luminance of targets across a scene and their three dimensional coordinates XYZ in the field. The high dynamic ...

Evaluating discomfort glare from non-uniform electric light sources

Abstract: This study tested the appropriateness of unified glare rating (UGR), CIE glare index (CGI), British glare index (BGI), and visual comfort probability (VCP) for evaluating discomfort glare from common non-uniform electric light sources. An experiment was conducted in a windowless room. High dynamic range photogrammetry was used for measuring three non-uniform fluorescent glare sources. The luminance and geometry data were acquired to calculate the glare ratings. The sub-divisibility and additivity of UGR, CGI, BGI, and VCP were tested via numerical method. Their predictability was evaluated using 67 subjects in two sessions. It was found that UGR, CGI, BGI, and VCP all have valid additivity, but only UGR and CGI have valid sub-divisibility. Current formulae of UGR, CGI, BGI and VCP all overestimate the glare sensation from non-uniform sources that young people may feel. Language: en

Target visibility level and detection distance on a driving simulator

Abstract: The visibility level (VL), a quality index in road lighting design, also serves to assess automotive lighting performance. Unlike illuminance levels, the VL provides a link between lighting design and driving performance. The reference performance of the VL is the detection of a small uniform target, standing on a uniform background (the road surface). Still, VL is subject to a number of caveats with regards to the driving task. We address the non-realistic nature of the reference target (a uniform square). A driving simulation experiment was conducted in a virtual night-time rural highway environment. The subjects drove along the road and came across different targets on the roadside. The detection distances were recorded and compared with the corresponding VL, showing rather good agreement.

Multi-objective optimisation of lighting installations taking into account user preferences – a pilot study

Abstract: A multi-objective methodology is proposed to optimise lighting solutions by taking into account not only energy objectives but also subjective ones such as visual preferences. The originality of this method lies in the integration of subjective data obtained from psycho-visual tests conducted with panels of observers potentially representative of end users, into a multi-objective optimisation framework. This method makes it possible to identify all the best tradeoffs and the direct correspondence between power demand and user visual preferences, to handle constraints, to handle inter-individual differences and to optimise preferences on various visual attributes at the same time. The methodology was developed through a pilot study of office lighting optimisation. The findings are consistent with previous work and provide additional application knowledge about the case study.

White lighting for residential applications

Abstract: The lighting industry relies on colour-rendering index (CRI) and correlated colour temperature (CCT) to communicate the colour properties of light sources. While advances have been made in recent y...

Residents’ perceptions following retrofitting of residential area outdoor lighting with LEDs:

Abstract: The use of light emitting diodes (LEDs) in outdoor lighting has energy-saving potential, but users' responses to this light source are largely unknown. An intervention study in two residential areas compared conventional lighting installations (high pressure sodium in Area 1 and high pressure mercury in Area 2) to a retrofitted LED-alternative regarding residents' perceptions of quality of light, visual accessibility and danger. Moreover, energy use was calculated. Residents' (N = 60) visual accessibility improved and perceived danger remained low in both areas after retrofitting. In Area 2 the perceived quality of light increased, whereas in Area 1 the results were mixed. The retrofitted application reduced energy use by 41-76% and might be a feasible alternative to conventional outdoor lighting in relatively safe areas. Language: en

Impact of daylight illumination on reducing patient length of stay in hospital after coronary artery bypass graft surgery

Abstract: In this research, a field investigation was done with 263 coronary artery bypass graft (CABG) surgery patients to identify the impact of daylight exposure on patient length of stay (LoS) in hospital. Lighting data were collected by installing sensors inside in-patient rooms, and were used to develop a multiple linear regression (MLR) model to explore the relationship between daylight intensity and patient LoS in the presence of other environmental (i.e. provision of outdoor view and room status) and clinical (i.e. mean arterial pressure, heart rate and diabetes mellitus) variables. The coefficient estimates of the developed MLR model suggest that while holding the other explanatory variables constant, the patient LoS reduced by 7.3 hours per 100 lx increase of daylight inside in-patient rooms.

Light-emitting diodes in street and roadway lighting - a case study involving mesopic effects

Abstract: The paper considers the justification for the application of light-emitting diode (LED) technology to urban lighting. The results suggest that LEDs are convenient for architectural lighting and deserve to be considered for use in ambient lighting. The recently developed Commission Internationale de l'Eclairage (CIE) mesopic system enabled the inclusion of mesopic effects into a comprehensive techno-economic analysis, which dealt with efficiency, maintenance and financial aspects of the use of LEDs in street and roadway lighting. It is concluded that the average energy savings when using LED instead of high-pressure sodium (HPS) luminaires amount to 19-26% for single-sided, staggered and opposite layouts, although they are frequently negligible if mesopic effects are not included. The total costs of the LED lighting solutions, even including mesopic effects, are 1.36 to 6.44 times higher than those of the comparable HPS lighting solutions. Therefore, LEDs are questionable for street and roadway lighting. Language: en

Validation of an online protocol for assessing the luminous environment

Abstract: We developed a web application in order to investigate online-based experiments for the psychovisual assessment of luminous environments. We reproduced online a laboratory experiment conducted in virtual environment, in which luminous environments of an office room lit by hybrid ambient/task lighting were assessed by observers. A control panel of 30 observers performed both experiments. Statistical analyses do not highlight statistically significant differences between data collected in laboratory and online. In addition, an online-based experiment involving 1114 observers was conducted to study the uncontrolled experimental conditions that may impact results. We show that, by increasing the panel size, bias mainly related to perceived contrast and brightness and brightness of surrounding area is removed. Findings suggest that a number of 100 observers would be enough.

The effect of different weather data sets and their resolution on climate-based daylight modelling

Abstract: Climate-based daylight modelling is based on the available weather data, which means that the weather data used as input to the daylight simulations are of great importance. In this paper, the effect on the outcome of the daylight simulations of using one weather data file rather than another for the same location was investigated. Furthermore, the effect of using weather data sets with an hourly resolution compared to a one-minute resolution was investigated. The results showed that the lighting dependencies varied by up to 2% depending on the chosen weather data file and indoor illuminance threshold. The energy consumption for artificial lighting was underestimated when simulating with time steps of hourly means compared to one-minute resolution. The findings from this comparison show that the dynamic, short-term effects of the weather have a surprisingly small impact on the simulation outcome.

Effect of different coloured luminous surrounds on LED discomfort glare perception

Abstract: Recently, there has been increased interest in energy-efficient lighting as energy resources become higher in demand. Anecdotal evidence suggests that certain populations believe light-emitting diodes (LED) produce more glare than traditional technologies. This may be due to a number of factors such as spectral power distribution (SPD), source luminance, or beam intensity distribution. A study was conducted to assess the effect of different SPDs on the perception of discomfort glare from an LED source. For the range of conditions evaluated, the presence of any luminous surround significantly reduced the perception of discomfort glare from the LED array. The blue luminous surround reduced discomfort glare perception significantly less than the white or the yellow luminous surrounds. The implications for solid-state lighting systems are discussed.

A simplified control system for a daylight-matched LED lamp

Abstract: Energy-conscious facility designs strive to include natural daylight in workspaces However, the correlated colour temperature (CCT) and spectral content of daylight varies throughout the day while existent electric lamps produce light with a fixed CCT, resulting in mixed-illumination environments A prototype LED lamp, with a simple control concept and a novel pulse-width modulation drive circuit, is proposed This white light over a broad range of CCT values while maintaining a stable colour quality fidelity score with respect to a standard daylight source having an equivalent CCT This range of CCTs is obtained without requiring computations for spectral approximation, resulting in a simplified control system

LRT Digest 1 Maintaining brightness while saving energy in residential roads

Abstract: This digest presents a summary of recent research on the relationship between lamp spectrum and brightness in the context of residential roads. Lighting design for such roads considers primarily the needs of pedestrians rather than drivers. For pedestrians, brightness is important because brighter lighting tends to produce higher levels of perceived safety in a particular location. Studies of brightness perception for lamps with different spectral power distributions at illuminances representative of those used for residential road lighting have been made using controlled laboratory conditions and field surveys. The findings from these two approaches are in good agreement. It has been found that in the mesopic region (the lighting levels found on roads at night time) lamps with a higher scotopic / photopic (S/P) ratio appear brighter at the same illuminance than lamps with lower S/P ratios. This means that lamps with a high S/P ratio can be used either at the same illuminance to create a higher brightness or at a lower illuminance but the same brightness, the latter leading to a reduction in energy consumption. The recently established CIE system of mesopic photometry, which involves S/P ratio, can be used to predict the illuminance reduction that will ensure the same level of brightness for a range of lamps with different spectra. However, brightness is not the only factor that matters for the lighting of residential roads. The ability to detect obstacles is also important, as is the appearance of the environment and the confidence that the intent and identity of other people can be recognised. Other studies have shown that the ability to detect obstacles is influenced by lamp spectrum in a similar manner to brightness, that is, a higher S/P ratio improves obstacle detection. As for the acceptability of the appearance of the environment, this is more consistently related to the colour rendering of the light source than the S/P ratio. How light spectrum affects the ability to recognise the intent of other people is still uncertain. Given these findings it is possible to modify the illuminances used in residential roads when using different light sources. These illuminances should be chosen based on two characteristic of the light source, S/P ratio and colour rendering index. The Institution of Lighting Professionals (ILP) have proposed two rules:1 Reducing illuminance from the levels recommended in the S-series of lighting classes can be considered when using lamps which have a CIE general colour rendering index greater than or equal to 60. Where lamps with a colour rendering index greater than or equal to 60 are to be used, the illuminance reduction allowed can be calculated using the CIE system of mesopic photometry, assuming the low pressure sodium lamp is the reference. The table below gives the examples of the illuminances predicted by this process for a number of alternative lamps for the S-classes given in BS 5489-1:2003 and BS EN 13201-2:2003. This demonstrates that MH lighting, for example, may be used at a lower average illuminance than HPS lighting, and this may lead to a saving in energy consumption. View this table: In this window In a new window Language: en

Extra-care housing for people with sight loss: Lighting and design:

Abstract: The study investigated whether United Kingdom-based extra-care housing, which provides older people with individual dwellings, communal facilities and care support, complies with current guidance on design for people with visual impairment and satisfies the needs of residents with sight loss. A total of 41 apartments/bungalows in 11 schemes were surveyed and interviews conducted with the occupants. Participants’ comments suggest the current specialist guidance on design for people with sight loss is sound, although there is scope for additional guidance on aspect and daylight, which were highly valued. Little of this specialist guidance is included in mainstream design guidance, which might explain some deficiencies in extra-care housing, including low lounge and bedroom illuminances, few dimmer switches, and limited use of colour to enhance the legibility of spaces.

Characterization of sky scanner measurements based on CIE and ISO standard CIE S 011/2003

Abstract: The aim of this paper is to present a complete analysis of the sky luminance distribution data measured with a sky scanner at the International Daylight Measurement Program station in Lyon. Besides...

Electric lighting at the workplace in offices: Efficiency improvement margins of automation systems

Abstract: Electric lighting is one of the major energy loads in non-residential buildings. It is strategic to examine the real behaviour of available lighting control systems for practical applications so as...

Boosting circadian rhythms with lighting: A model driven approach:

Abstract: We describe a model-based strategy for defining an optimal lighting schedule for strengthening the circadian rhythms of patients in intensive care units as a means of reducing delirium rates in hos...