A Proposal for an Integrated Model to Evaluate the Circadian Effects of Mesopic Light Sources

With the increasing attention on circadian effects driven by light,lighting industry has inspired a revolution of photobiological lighting design.Due to diverse evaluation criteria for visual and non⁃visual systems,models that combine these evaluation parameters are indeed urgent.Thus,an integrated model for mesopic lighting evaluation of circadian effects was proposed.The circadian efficiency function adopted in this study was synthesized by CIE 1931 XYZ 2 deg color matching functions and standard scotopic sensitivity function.Then,the integrated model composed of International Commission on Illumination 1931 xy chromaticity coordinates,scotopic/photopic ratio,and illuminance could be obtained with synthesized circadian efficiency function.The model showed that for light sources with fixed chromaticity coordinates and fixed illuminance,enhancing the circadian effects is equivalent to increasing the scotopic/photopic ratio,which suggests a useful method for practitioners to explore the photobiologically reasonable spectrum for mesopic lighting.Light⁃emitting diodes spectra optimized by four⁃component color⁃mixing method were employed to figure out the property of the integrated model.

Literature Review about spectral sensitivity of the eye

The visible portion of spectrum covers the wavelength range from approximately 380nm to 780nm and the eye discriminates between different wavelengths in this range by the sensation of colour.

Lens density measurements by two independent psychophysical techniques

Background:Cataract,a leading cause of vision impairment,is due to the lens becoming excessively optically dense.Change in the lens optical density(LOD)could be a useful indicator of incipient nuclear cataract and would necessitate the development of accurate measurement techniques.Mapcat sf^(TM) is a heterochromatic flicker photometer for measuring macular pigment optical density(MPOD)under photopic conditions.In the process,it also measures LOD that is needed in the calculation of MPOD.LOD is then converted by the instrument to“lens equivalent age”(LEA).However,varying cone photoreceptor ratios among individuals could affect the LEA measurement.Scotopic vision is mediated by rod photoreceptors;therefore,LEA measurement under scotopic conditions potentially provides a reliable standard for assessing other methods.The study was conducted to test the level of agreement between the LEA data obtained under photopic and scotopic conditions for a sample population.We also comment on factors that might contribute to any disagreement.Methods:LEAs were obtained by Mapcat sf for 25 subjects and compared with those obtained under absolute scotopic threshold conditions.Results:The mean scotopic LEA for the subjects was 2.7 years higher than the mean photopic LEA,but this difference was not statistically significant.Measurements by the two methods were reasonably correlated(r 2=0.59,p<0.0001).Significant individual differences in LEA by the two methods were found for six of the 25 subjects.Although our calculations included a standard long-to medium-wavelength-sensitive cone ratio,we found that different ratios could be found that rendered the differences in LEA insignificant for two of these six subjects.Variability in pupil diameter during scotopic measurements was considered another potential source of discrepancy between LEAs by the two methods.Conclusion:The absolute threshold technique,with long adaptation times,is probably impractical for routine lens density measurement,whereas Mapcat sf provided a rapid,straightforward test that may find its application in optometric/ophthalmic practice.