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Iain Carlile selects four of the latest LR&T papers to be published online, which all focus on various aspects of white light LEDs

Four of the most recently published papers look at the application of white light LEDs from a range of perspectives: with respect to glare, artwork conservation, life-cycle assessment and the relationship between CRI and luminous efficacy. On the subject of glare, Huang et al’s paper describes an experiment investigating discomfort glare caused by differing spectral power distributions (SPD) in white LEDs. Two sets of experiments were conducted, the first to investigate the effect of LEDs with the same perceived appearance, but having a different SPD (metamerism), and the second the effect of varying the correlated colour temperature (CCT). It was found from the metamerism investigation that 7000K light sources constructed from varying blue LEDs combined with consistent red and green LEDs resulted in similar glare perception between the different sources. In the CCT investigation light sources between 3000K and 7000K, with 1000K increments, were used. It was found that there was a significant difference in glare perception between the varying CCT values, with higher CCT values producing higher perceived glare. Examining the conservation of artworks, specifically traditional heavy colour Chinese paintings, Dang et al investigated optimising the white LED spectrum to minimise damage to the painting. The authors used narrowband spectra LED light sources to illuminate the paintings and measured the CIELAB colour data at periodic intervals. From this data, decay curves were constructed according to the different pigments used in the artworks. From an analysis of the data, both quantitative and relative influence coefficients were determined for each narrowband light type. The authors make recommendations for different spectral irradiance distributions for lighting different types of Chinese paintings, including fine brushwork with rich and deep pigments, heavy colour golden paintings, and artworks with strong green heavy colours. Casamator et al looked at the total life cycle of LED lighting, conducting cradle-to-grave assessments with the aim of informing the ‘eco’ design of new LED lighting products. Using a novel assessment method more suited to LEDs than traditional sources, the study considered all elements in the life cycle, excluding maintenance and packaging manufacture. Different scenarios were considered at different useful lives (1000, 15,000 and 40,000 hours) and different end-of-life options (domestic refuse and recycling centre). The authors found that new ‘eco’ lighting products had 60 per cent less environmental impact in all scenarios when compared with existing lighting products. It was found that the life-cycle stages with the biggest impact were (largest first): use, followed by manufacturing, then end of life and, lastly, transport. Clearly from this analysis the energy in use has the biggest impact and strategies to reduce this will yield the greatest savings over time. Zhou et al examined the trade-off between the CRI and



Optimising the white LED spectrum to minimise damage to Chinese traditional heavy colour paintings (Dang et al)

luminous efficacy of a white light chip-on-board (COB) LED. The authors found that adding red phosphor (655nm) into the phosphor layer of a COB LED can broaden the emission spectrum, significantly improving the CRI of the LED light source, while not greatly compromising the luminous efficacy. Iain Carlile, MSLL, is an associate of DPA Lighting Lighting Research and Technology: OnlineFirst In advance of being published in the print version of Lighting Research and Technology (LR&T), all papers accepted for publishing are available online. SLL members can gain access to these papers via the SLL website. Discomfort glare caused by white LEDs having different spectral power distributions WJ Huang, Y Yang and M Ronnier Luo White LED spectrum for minimising damage to Chinese traditional heavy colour paintings R Dang, Y Yuan, G Liu, C Luo and J Liu Comparative life-cycle assessment of LED lighting products JL Casamayor, D Su and Z Ren LED chip-on-board package with high colour rendering index and high luminous efficacy Z Zhou, H Wang, J Zhang, J Su and P Ge

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SLL July/August 2017  

SLL July/August 2017