May 2024 - MeLiDos WP3 update: Insights into spatially resolved light logging devices
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 consider filling in our 10 - 20 min online survey: https://forms.office.com/e/uAQQgCqMkB. For more information on the activities related to spatially resolved light loggers or direct exchanges, feel free to contact 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.