TY - JOUR

T1 - Comparison and Correction of the Light Sensor Output from 48 Wearable Light Exposure Devices by Using a Side-by-Side Field Calibration Method

AU - Markvart, Jakob

AU - Hansen, Åse Marie

AU - Christoffersen, Jens

PY - 2015/1/1

Y1 - 2015/1/1

N2 - Measurement of personal light exposures and activity has gained popularity in studies of the circadian rhythm and its effects on human health. Calibration of a batch of measuring devices may be needed, especially before initiating interventional studies, but manufactory calibration of devices before every initiated study is costly for the researcher and therefore often left out. Still, knowledge of inter-equipment variability is essential and seldom provided by the manufactory. The aim of the present study was to develop and test a method for field calibration of Actiwatch Spectrum devices. We tested 48 Actiwatch devices side by side under various light sources and present the red, green, blue, and white light response variability among the Actiwatches. The influence of different spatial and spectral light environments on the white light response when compared with the output from a calibrated photometer is discussed. In agreement with previous studies by Price and others [2012] and Figueiro and others [2013], we confirm the devices white light responses to be highly dependent on both the spatial and the spectral composition of the light. The white light response represents photopic illuminance only to a minor degree and light source-specific calibration may therefore be needed in some cases. Moreover, light responses were found to vary between devices by up to 60%. Implications are that the results of light effects on health issues in studies using Actiwatches are blurred by the equipment variability. To compensate for inter-equipment variability we stress the need for a field calibration procedure. When light exposure devices of lower grade quality are used in spectrally and spatially changing light environments, daylight from a diffused overcast sky is suggested to be used for side-by-side calibration of Actiwatches and similar personal light exposure devices.We suggest that the calibration methods presented can be used for calibration of other practical field devices, with respect to the various sensors already on the market and devices that will be introduced in the future.

AB - Measurement of personal light exposures and activity has gained popularity in studies of the circadian rhythm and its effects on human health. Calibration of a batch of measuring devices may be needed, especially before initiating interventional studies, but manufactory calibration of devices before every initiated study is costly for the researcher and therefore often left out. Still, knowledge of inter-equipment variability is essential and seldom provided by the manufactory. The aim of the present study was to develop and test a method for field calibration of Actiwatch Spectrum devices. We tested 48 Actiwatch devices side by side under various light sources and present the red, green, blue, and white light response variability among the Actiwatches. The influence of different spatial and spectral light environments on the white light response when compared with the output from a calibrated photometer is discussed. In agreement with previous studies by Price and others [2012] and Figueiro and others [2013], we confirm the devices white light responses to be highly dependent on both the spatial and the spectral composition of the light. The white light response represents photopic illuminance only to a minor degree and light source-specific calibration may therefore be needed in some cases. Moreover, light responses were found to vary between devices by up to 60%. Implications are that the results of light effects on health issues in studies using Actiwatches are blurred by the equipment variability. To compensate for inter-equipment variability we stress the need for a field calibration procedure. When light exposure devices of lower grade quality are used in spectrally and spatially changing light environments, daylight from a diffused overcast sky is suggested to be used for side-by-side calibration of Actiwatches and similar personal light exposure devices.We suggest that the calibration methods presented can be used for calibration of other practical field devices, with respect to the various sensors already on the market and devices that will be introduced in the future.

KW - Illuminance meter

KW - Photopic illuminance

KW - Photopic vision

KW - RGB light

KW - Scotopic vision

KW - Spectral power distribution (SPD)

U2 - 10.1080/15502724.2015.1020948

DO - 10.1080/15502724.2015.1020948

M3 - Journal article

AN - SCOPUS:84944747357

VL - 11

SP - 155

EP - 171

JO - LEUKOS - Journal of Illuminating Engineering Society of North America

JF - LEUKOS - Journal of Illuminating Engineering Society of North America

SN - 1550-2724

IS - 3

ER -