Abstract
Several models on the circadian effect have been applied to indoor circadian lighting design, but applications in road lighting have not yet been clarified. Based on existing models and circadian research, we examined equivalent melanopic lux (EML), circadian light (CLA), and circadian stimulus (CS) representing the circadian effect and the S/P ratio representing the mesopic vision effect, among a dataset of light sources at photopic adaptation illuminance values of 1, 3, 10, 30, and 100 lx. The results show that the S/P ratio correlates with EML and CS (or CLA) much stronger than it correlates with color temperature. The EMLs of light sources are below 50 EML in mesopic vision, and the CSs of most light sources are below or around the threshold value of 0.05. We conclude that the circadian effect is not a significant issue in mesopic vision under most conditions and that optimization for mesopic efficiency is still a good strategy. There are quite a few light sources that may achieve both ideal mesopic efficiency and low CS. This work clarifies the circadian effect and mesopic vision effect performance of light sources in mesopic vision and will help guide choosing suitable light sources and optimization strategies for road lighting.
Highlights
There are two kinds of visual imaging photoreceptors [1], cone and rod cells, and one kind of non-visual imaging photoreceptor, intrinsically photosensitive retinal ganglion cells (ipRGCs) [2,3]
If the yellow stimuli dominate, only the intrinsic sensitivity of the ipRGC contributes to the circadian response; otherwise, all photoreceptors contribute to the circadian response
The equivalent melanopic lux (EML) is linear to the illuminance value, so the EML values at different illuminance levels can be achieved by multiplying by an intensity factor k of 3, 10, 30, and 100
Summary
There are two kinds of visual imaging photoreceptors [1], cone and rod cells, and one kind of non-visual imaging photoreceptor, ipRGCs [2,3]. For the visual imaging system, the activation levels of the cones and rods differ at different luminance (or illuminance) ranges. Road lighting is mainly in the mesopic vision stage, where both cones and rods activate. For non-visual imaging systems, melatonin suppression occurs under a large range of illuminance levels, even as low as 1 lx [6]. A few works [7] focused on dim outdoor lighting applications (
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