Evaluation methodology for light sources used to illuminate highly photosensitive artwork

Spectral energy radiated by light sources is the primary source of colour damage in highly photosensitive artworks (HPAs). However, spectral power distributions differ for different light sources, and the absorption and reflection characteristics of different materials, when irradiated by each narrow spectral energy band, also differ. This could result in large differences in the degree of radiation damage for materials under the same lighting intensity. In this paper, the suitability of different light sources used to illuminate HPAs was experimentally investigated over a long period of time by irradiating nine types of typical HPA materials with 10 different narrow-band light sources. By analysing the colour difference data of the illuminated material against the amount of exposure, a mathematical model relating the spectral composition and the damage to the colour of HPA materials was obtained. Based on this, a colour damage evaluation equation for light sources used for lighting HPAs was proposed. Finally, the equations were discussed using an example.

An examination of range effects when evaluating discomfort due to glare in Singaporean buildings

This article discusses ratings of visual discomfort from glare across different buildings located in Singapore. These data were used to determine if range effects influence the vertical illuminance values for the same ratings of visual discomfort when the category rating procedure is used. The effect occurs when maxima and minima vertical illuminance (i.e. the range) vary across buildings. Our analyses showed that with a higher vertical illuminance range in a building, the mean vertical illuminance value for the same criterion of visual discomfort also increased. The results suggest that the effect caused by different ranges of measured vertical illuminance present across the buildings biased the ratings of visual discomfort. Although these effects may be unavoidable in some buildings that have vastly different levels of light, the data suggest that the overall range of vertical illuminance must be carefully evaluated when predicting visual discomfort. Matching these conditions may enable vertical illuminance to provide more reliable evaluations of discomfort due to glare.

Algorithm for real-time colour mixing of a five-channel LED system while optimising spectral quality parameters

Multichannel LED luminaires with more than three channels offer the advantage to vary the spectrum and keeping the chromaticity steady. However, the optimisation calculations of various quality metrics are a challenge for real-time implementation, especially for the limited resources of a luminaire’s microcontroller. Here, we present a method in which a five-channel system is simulated with a quickly solvable 3-channel system by defining virtual channels, each consisting of two LED channels. An analysis of the influence of the parameterisation of the virtual valences on various quality metrics is presented. It shows how these parameters must be set at the time of the mixing calculation, in order to optimise the desired quality aspect. The mixing calculation can thus be carried out in real-time without high hardware requirements and is suitable for further developments, for example, to compensate for colour drift of the LEDs through sensor feedback.

A simple design of uniform LED illumination using catadioptric collimator and freeform lenslet array

We introduce a compact lenslet array principle that takes advantage of freeform optics to deploy a light distributor, beneficial for highly efficient, inexpensive, low energy consumption light-emitting diode (LED) lighting system. We outline here a simple strategy for designing the freeform lens that makes use of an array of the identical plano-convex lenslet. The light is redistributed from such lenslet, hinging on the principle of optical path length conservation, and then delivered to the receiver plane. The superimposing of such illumination area from every lenslet occurs on the receiver plane, in which the non-uniform illumination area located in the boundary should have the same dimension as the size of the freeform lenslet array. Such an area, insofar, is negligible due to their small size, which is the crux of our design, representing a large departure from the former implementations. Based on simulations that assess light performance, the proposed design exhibited the compatibility for multiple radiation geometries and off-axis lighting without concern for the initial radiation pattern of the source. As simulated, the LED light source integrated with such proposed freeform lenslet array revealed high luminous efficiency and uniformity within the illumination area of interest were above 70% and 85%, respectively. Such novel design was then experimentally demonstrated to possess a uniformity of 75% at hand, which was close to the simulation results. Also, proposed indoor lighting was implemented in comparison with the commercial LED downlight and LED panel, whereby the energy consumption, number of luminaires and illumination performance were assessed to show the advantage of our simplified model.

Gaze correlates of view preference: Comparing natural and urban scenes

When looking out of a window, natural views are usually associated with restorative qualities and are given a higher preference than urban scenes. Previous research has shown that gaze behaviour might differ based on the natural or urban content of views. A lower number of fixations has been associated with the aesthetic evaluation of natural scenes while, when looking at an urban environment, a high preference has been correlated with more exploratory gaze behaviours. To characterise gaze correlates of view preference across natural and urban scenes, we collected and analysed experimental data featuring subjective preference ratings, eye-tracking measures, verbal reasoning associated with preference and nature relatedness scores. Consistent with the literature, our results confirm that natural scenes are more preferred than urban views and that gaze behaviours depend on view type and preference. Observing natural scenes was characterised by lower numbers of fixations and saccades, and longer fixation durations, compared to urban views. However, for both view types, most preferred scenes led to more fixations and saccades. Our findings also showed that nature relatedness may be correlated with visual exploration of scenes. Individual preferences and personality attributes, therefore, should be accounted for in studies on view preference and gaze behaviour.

A field test of a simplified method of estimating circadian stimulus

Residents of nursing homes often have a very limited access to natural daylight, which is the main environmental cue for circadian entrainment that usually cannot be compensated by standard indoor lighting. For the development of adequate modernization strategies with regard to a more human-centred lighting approach, reliable field measurements of the circadian effectiveness of the prevalent lighting conditions are required. To ease the task for the lighting practitioner, our lab recently developed a simplified method of estimating the biologically meaningful circadian stimulus (CS) metric using standard measurement equipment. In this work, the proposed method is applied for the first time in field measurements to assess the circadian effectiveness of the indoor light conditions including daylight entry of a nursing home in the Frankfurt Rhine-Main area. Reference thresholds for low, moderate and high circadian stimuli derived from the literature were used for subsequent data analysis. Mostly, moderate to rather low CS values were found. It is concluded that the amount of circadian-effective light is insufficient to provoke proper circadian stimulation, which may lead to progressive circadian disruptions manifesting in adverse effects on the residents’ health and well-being. Further evidence is provided that the insufficient-lighting-situation in nursing homes is a serious problem in long-term care and needs urgent consideration in health policy.