News - MeLiDos

Summer 2025 - Newsletter #4 and CIE midterm meeting in Vienna

Fabien Eloi — Wed, 03 Sep 2025 15:11:34 +0000

A big event for the lighting industrial and scientific communities this summer was the CIE (International Commission on Illumination) midterm meeting in Vienna, from July 4 to 11. Several MeLidos participants attended the scientific conference and the following Technical Committee meetings.

Some of the MeLiDos members attending the CIE Midterm conference

Summer conferences

The CIE scientific conference included many interesting topics, with no small amount of presentations and discussions around lighting and human health, highlighting the necessity for further research in the domains to which MeLiDos contributes. The MeLiDos team presented results on field measurements in a talk by Sofia from FUSP-CEU, as well as 3 presentations to the JTC20 to which MeLiDos contributes, including results on laboratory characterization of light loggers, the LightLogR software and data validation and device limitations in field measurements.

Results from the laboratory characterization of UV dosimeters will also be presented in the 3rd European Conference on Solar UV Monitoring and Personal UV Exposure, also in Vienna from the 9th to 11th of September.

Publication of our 4th Newsletter

Our 4th Newsletter has been published on the 1st of September, highlighting the progress made in the different activities of MeLiDos. This includes wearable light loggers laboratory characterization results, progress on the field data measurements and developped data methods, as well as the current status of our developments for spatially resolved light loggers.

The MeLiDos team also published 5 data sets from the field data collection carried out within the consortium and also by collaborators. They are available on Zenodo. Further updates to the available materials on the website are also expected in September following our upcoming meeting in September.

March 2025 - Publication of the 3rd Newsletter: Update at midterm

Fabien Eloi — Mon, 17 Mar 2025 15:07:54 +0000

Recently, project 22NRM05 - MeLiDos reached its midpoint. This is an occasion to review what has been achieved so far through our several newsletters, in particular our newly released 3rd edition. Please check out a summary below and find the complete newsletters here.

The MeLiDos team met in November 2024 at METAS, Bern, Switzerland for the Month 18 meeting.

Update on device characterisation

Three different models of solar UV dosimeters and four models of wearable light loggers have been acquired and distributed among the partners. The process of determining suitable characterization methods is ongoing, with several ideas being tested.

Characterization under skylight of solar UV loggers in Davos, Switzerland

Right now the methods being tested are compared to usual laboratory calibration procedures to select the most suitable ones for logger-type devices. As an example, a light logger which records a data point every 10 seconds would take a long time to have its spectral sensitivity evaluated with conventional methods. Using a set of well-selected LED emmitters would provide a cost- and time-efficient alternative albeit with degraded uncertainty, which would regardless not be a major issue in field measurements where measurement uncertainty comes primarily from device position, wearer movement, etc.

Field data collection

Data collection started in fall 2024 in some of our 6 selected sites and will be completed by the beginning of summer 2025 by all partners. There is great collaboration between the partners for the transfer of experiences from field measurements, dosimeter use and survey procedures. Several stakeholders have also approached the Consortium to use or adapt the data collection protocol and software developed in the project and already published.

Picture of the participants with the dosimeters

On that particular note, we are delighted to see ever more interest in the software package LightLogR from research groups all around the world. Notably, the package nears publication in the Journal of Open Source Software (JOSS, access the preprint here). We are preparing a major update that will bring solar-time-based functionality to the package - enabling powerful calculations and visualizations based on dusk, dawn, noon, etc. Look out for LightLogR 0.5.0 "Civil dawn“ in the coming days!

Towards spatial resolution in light logging

The WP3 team has completed its investigation into the privacy issues posed by spatially resolved light loggers. This analysis drew on several similar use cases, including dash cams, CCTV, and Google Street View. In summary, the proposed mitigation strategies include minimizing the amount of data collected, using built-in blur algorithms before exploiting high-resolution images, securing data storage and transfer, and making the data processing methods and technical details publicly available. Furthermore, the team also formulated recommendations for characterizing spatially resolved devices, based on the technical report CIE 244:2021 (Characterization of Imaging Luminance Measurement Devices) and their experience with conventional light loggers.

On the technical front, the team is continuing to develop data methods for camera-based devices, both to compare to and expand on existing metrics in light dosimetry. The team has also identified two promising directions for a PoC spatially-resolved light dosimeter, and hope to disclose more in the next newsletter this summer.

May 2024 - MeLiDos WP3 update: Insights into spatially resolved light logging devices

Fabien Eloi — Mon, 13 May 2024 12:53:04 +0000

Note: As our work is by no means exhaustive, if you have experience with traditional light loggers and want to provide us with ideas or feedback regarding spatially resolved devices, please reach out to our Work Package 3 leader.

Historically, personal light logging has focused on measuring illuminance, thereby enforcing a cosine weighting on the light’s angle of incidence. While this is an established method and a convenient simplification, it does not adequately represent the light actually reaching the sensitive parts of the eye. Moreover, the ipRGCs, the cells responsible for the regulation of melatonin and the circadian rhythm, are distributed anisotropically in the eye, peaking in their density not in the most central spot where our vision is sharpest – the fovea – but a few millimetres to the side. The use of cosine-corrected or spatially averaging light loggers therefore leads to a loss of information. Furthermore, most dosimeters do not take variations of the field of view into account due to e.g. changes in eyelid position or pupil size. These effects can be taken into account by using spatially resolved light logging devices, which are being investigated and developed in WP3 of MeLiDos.

Several recent studies have investigated this effect by measuring the contributions of spatial features of a scene to the response of the eye in the lab or using apparatuses to simulate eyelid position on light loggers. In our MeLiDos project, our goal is to ensure that light logger measurements is repeatable and representative by introducing metrology to the characterisation of the devices, and recommendations for their selection and use. This should extend to future light logger development including devices that can resolve spatial features. Work Package 3 of MeLiDos will focus on developing a proof of concept of a spatially resolved device in order to provide recommendations for future development, characterization and use of such spatially resolved light loggers. Such device could be based on either 1D or 2D matrix sensors with filters or on micro-cameras.

Figure from J. Zauner et al. (1)

Early work has identified several benefits and drawbacks of spatially resolved light loggers:

Benefits are mainly related to activity identification and field of view. Such device would provide additional ways to assert if the device is worn or not, covered, if the subject is outside, etc. which would help with data verification and consolidation. Scene contrast and light source identification could also be of benefit for indoor applications to monitor the percentage of daylighting or identify situations with glare.
Drawbacks are mainly related to design considerations. A spatially resolved light logger will need more complex hardware and data processing/storing capabilities, which may result in a loss of autonomy and wearability. Another aspect will be the increased complexity of characterisation and data analysis, which we aim to tackle in MeLiDos. Last but not least, imaging devices are bound to induce privacy issues. While data pre-processing can to some extent negate actual privacy concerns, it does not change how such device will be perceived by other people interacting with the wearer.

Further work will focus on developing characterisation methods appropriate for spatially resolved light loggers based on other MeLiDos results and CIE 244:2021, a Technical Report dealing with the characterisation of camera-based luminance measurement devices.

(1) Zauner, J.; Broszio, K.; Bieske, K. "Influence of the Human Field of View on Visual and Non-Visual Quantities in Indoor Environments“. Clocks & Sleep 2023, 5, 476-498.

19 June 2023: Kick-off meeting at LNE in Paris

Manuel Spitschan — Mon, 19 Jun 2023 16:15:00 +0000

The European project MeLiDos piloted by French Metrology Institute LNE had its kick-off meeting on Monday 19th, 2023. The project (22NRM05 MeLiDos) has received funding from the European Partnership on Metrology, co-financed from the European Union’s Horizon Europe Research and Innovation Programme and by the Participating States.”

With a duration of 3 years, its goal is to introduce metrology practices to the measurement of light at the personal dose level, more specifically to wearable light loggers. With 16 partners from 10 different countries, the metrology, chronobiology and photobiology experts will aim to provide guidelines for the characterisation and use of this kind of device, improving upcoming studies on the impacts of light on health and physiology.

Wearable light dosimeters applications have grown in recent years following the discovery of new receptors in the eye 20 years ago. These receptors sensible to blue light are not involved in vision but in regulating several physiological processes collectively called “non-visual” effects. These processes notably include the circadian rhythm and can negatively affect health and wellbeing if disturbed, for example by inappropriate lighting conditions. Wearable solar UV dosimeters are also used to monitor the UV dose received and estimate potential risks of skin cancer.

Current characterisation and calibration methods, such as those used for illuminance meters, are inappropriate for wearable devices that are supposed to be used in large quantities and suboptimal conditions. This is due to their cost and time constraints that are unsuitable for characterising a fleet of e.g. 50 sensors for a single study. In addition, there is no current guidelines on the selection and use of these devices for specific studies. While current researchers and users often do their best with the means and knowledge they have, not all are metrology or optics experts.

This project will introduce new characterisation methods designed to be faster and easier to implement, as well as provide guidelines for selecting and using the devices suitable for different applications. In addition, tools will be developed to help users verify, validate, understand and analyse the data collected by wearable light loggers. This will make research in the field more reliable and in turn provide policy makers with solid background to improve global health and wellbeing.