Metrology for solid-state lighting quality (Visual comfort metric) J. Nonne, D. Renoux – LNE L. Rossi – INRIM jordi.nonne@lne.fr

Introduction Some years ago, few lightings based on LEDs were introduced on the market with low flux and efficiencies; today, a full range of products with high efficiencies and flux are available. These technologies present many advantages (greater lifetime & efficiency, less thermal hazard,…) but, Present properties quite different compared to traditional light sources. LED devices, feature many and different types of spectral power distribution, they can have small emitting area and strong directivity with high luminance level, … Current quality metrics for lightings were developed for previous technologies (tungsten, fluorescent,…), and poorly predict the quality of these new types of light sources. New metrics for lighting have to be developed to specify correctly lighting quality of these new technologies.

Introduction LNE contributed to ENG05 lighting (2010-2013): a project of the European metrology research programme. In this project, we addressed with partners: - Life time - Colour rendering - Visual comfort Comfort experiments were conducted at LNE with the participation of an INRIM scientist.

Introduction Visual Comfort is usually measured by the degree of discomfort (glare or flicker indices) and managing a comfortable environment is done using basic light rules (level, luminous ratio: area of interest / surround,…). (Unified Glare Rating (UGR), EN12464, …) Our approach consisted the determination of a global degree of comfort as a combination of different properties of lighting environment : Subjective Physical Human assessment characterisation characterisation Visual comfort model

Experiment design 4 lighting experiments were performed with: -glare setup (5 evaluations) -living room (4 configurations) -compartment (4 configurations) -office (4 configurations) 50 subjects participated: -18 to 62 year old (mean 36) -52% female 48% male -half morning / half afternoon -54% light iris / 46% dark iris Levels Distributions (angular) CCT(Correlated color temperature) Technologies Listing Watching Reading Writing Using Different task

Pictures of the 4 experiments

Physical characterisation: Spectral power distribution Spectral power distribution (SPD) & illuminance level of each configuration were measured in situ at the eyes position and integrated on the entire field of view. Relative luminance Relative luminance Relative luminance Relative luminance

Physical characterisation : luminance map Photometric camera mounted on 2 axis-gonio: acquisition features: 1024*1024px, ~15° aperture 9*8=72 positions (giving a total aperture ~ ±60° by ± 67° ) - 3 integrating times - 3 optical densities =>648 pictures of the scene recombined to output a luminance map : -in teta-phi coordinates -a table of 4096*4096 luminance level values -log transformation for visualisation

Physical characterisation : luminance map LED diffuse 1 LED Diffuse 2 Halogen LED Spot

Physical characterisation : luminance map Views of 4 compartments Views of the 2 desks and with their two lighting configurations Halogen - Warm LED Halogen & FL tube - CFL & FL tube Neutral LED - Cold LED LED spot & LED tube - LED diffuse & LED tube

Psycho characterisation Eyes tracking system : 3 cameras recording: - the field of view - the two eyes Data outputs : - gaze positions (after calibration) - gaze events (saccade, fixation,blink) - pupils sizes INRIM data proceeding – gaze event’s results were presented at the ECEM congres 2013 (Sweden)

Results: aperture of pupils Luminous approach (flux regulation): (Dpupils)² ∝ 1/Luminance =>study shows the effects of blue content (Bleu was defined here as the wavelength < 480nm) =>introduction of a linear factor depending of blue content A good correlation is obtained (Pearson coef: 0.99)

Results: glare 1/3 source CIE formula for classical sources: ωn: Solid angle of the source Ln=luminance of the source CIE formula for small sources: Same but L² * W = I² * 200 / R² eyes Field of view Pn: Guth position (depending of source’s position in the field of view) Lb =Background luminance

Results: glare 2/3 CIE UGR (for small source) Yields to bad correlation with our experiment CIE UGR (normal formula) Leads to good correlation Even in complex situations (experiment in living room) Visual comfort is not slightly impacted by glare because UGR value is small => then other parameters of visual comfort have to be considered.

Results: glare 3/3 Experiment 1 used a comparative evaluation of glare. Experiment 2 used a fixed-scale. We obtained : “imperceptible” for a 07 UGR value “just perceptible” for a 13 UGR value “just tolerable” of a 20 UGR value We have a good correlation but the scales are different. Many papers found contradictory results=> More investigations have to be performed

Results: comfort 1/3 Considered discomfort parameter: - only glare was took into account (no flickering effect) Considered comfort parameters: - Light levels - Uniformity / light patterns - Shadow effects - CCT / spatial variation of CCT - Colour rendering - Luminaire appearance - Areas of interest (Light levels, distributions,…)

Results: comfort 2/3 Development of a visual comfort: dissociation of comfort and discomfort parameters Discomfort parameter (glare) inhibits other parameters

Results: comfort 3/3 Parameters weighting are depend on the configurations: Office desk: require uniformity for task realisation living room: require object shadow for volume and pleasantness. Good correlation are obtained: Pearson coefficient for 3 environments are respectively : 0.94 0.91 0.97

Conclusions on lights using LED technology Objective predictions of the visual comfort model are well correlated to subjective ratings for 3 different experiments. The model needs to be refined and validated with new lighting situations. CIE UGR (glare) relative value fit well subjective results, nevertheless more investigations are needed in order to study complex environments and set an absolute scale. Using human as a measurement system revealed us some behaviours well correlating to the degree of perceived visual comfort.

EMRP EMRP supports the collaboration of European metrology institutes, industrial organisations and academia through Joint Research Projects (JRPs). It is structured around European Grand Challenges in such areas as Health, Energy, the Environment & New Technologies. This presentation is one of 17 presentations, 5 posters and 2 workshops at this conference supported by the European Metrology Programme, implemented by EURAMET. The last call for EMRP proposals has just closed – but we look forward to its successor - EMPIR. See www.euramet.org for more details. SI Units (2011 & 2012) Environment (2010 & 2013) Energy (2009 & 2013) Energy (2009 & 2013) New Technologies (2011) Health (2011) Industry (2010 & 2012) 20