Data from: Nature, extent and ecological implications of night-time light from road vehicles

1.The erosion of night‐time by the introduction of artificial lighting constitutes a profound pressure on the natural environment. It has altered what had for millennia been reliable signals from natural light cycles used for regulating a host of biological processes, with impacts ranging from changes in gene expression to ecosystem processes.

2.Studies of these impacts have focused almost exclusively on those resulting from stationary sources of light emissions, and particularly streetlights. However, mobile sources, especially road vehicle headlights, contribute substantial additional emissions.

3.The ecological impacts of light emissions from vehicle headlights are likely to be especially high because these are (i) focused so as to light roadsides at higher intensities than commonly experienced from other sources, and well above activation thresholds for many biological processes; (ii) projected largely in a horizontal plane and thus can carry over long distances; (iii) introduced into much larger areas of the landscape than experience street lighting; (iv) typically broad ‘white’ spectrum, which substantially overlaps the action spectra of many biological processes; and (v) often experienced at roadsides as series of pulses of light (produced by passage of vehicles), a dynamic known to have major biological impacts.

4.The ecological impacts of road vehicle headlights will markedly increase with projected global growth in numbers of vehicles and the road network, increasing the local severity of emissions (because vehicle numbers are increasing faster than growth in the road network) and introducing emissions into areas from which they were previously absent. The effects will be further exacerbated by technological developments that are increasing the intensity of headlight emissions and the amounts of blue light in emission spectra.

5.Synthesis and applications. Emissions from vehicle headlights need to be considered as a major, and growing, source of ecological impacts of artificial night‐time lighting. It will be a significant challenge to minimize these impacts whilst balancing drivers’ needs at night and avoiding risk and discomfort for other road users. Nonetheless, there is potential to identify solutions to these conflicts, both through the design of headlights and that of roads.

1. 人工照明的普及正不断侵蚀夜间天然时段，已对自然环境构成深远压力。数千年来，自然光周期一直是调控众多生物过程的可靠信号，而人工照明改变了这一信号，其影响范围涵盖基因表达（gene expression）改变直至生态系统过程（ecosystem processes）。
2. 针对此类光污染影响的研究，几乎完全聚焦于固定光源的光辐射排放，尤以路灯为主。然而，移动光源——尤其是道路车辆前照灯——也会带来大量额外的光辐射排放。
3. 道路车辆前照灯的光辐射对生态系统的影响可能尤为显著，原因如下：(1) 其光线聚焦于道路两侧，光照强度高于其他常见光源，且远超众多生物过程的激活阈值（activation thresholds）；(2) 光线主要沿水平面投射，因此可传播至较远范围；(3) 其覆盖的景观区域远大于路灯照明的范围；(4) 通常具有宽泛的“白色”光谱，与众多生物过程的作用光谱（action spectra）高度重合；(5) 道路两侧的光照往往呈现为车辆驶过产生的一系列光脉冲（pulses of light），这种动态光照模式已被证实会产生重大生物学影响。
4. 随着全球车辆保有量与道路网络的预计增长，道路车辆前照灯的生态影响将显著加剧：一方面，车辆保有量的增速快于道路网络扩张，导致局部光辐射污染的严重程度提升；另一方面，光辐射排放被引入此前从未有此类污染的区域。此外，不断提升前照灯光辐射强度与光谱中蓝光占比的技术发展，将进一步加重其负面影响。
5. 总结与应用。车辆前照灯的光辐射排放，应被视为人工夜间光照明（artificial night-time lighting）生态影响的一项主要且日益严峻的来源。在兼顾夜间驾驶需求、避免对其他道路使用者造成安全风险与不适的同时，尽可能降低此类影响，将是一项重大挑战。尽管如此，通过优化前照灯设计与道路设计，仍有潜力找到化解此类冲突的解决方案。