Light at dawn and dusk is the key signal for the entrainment of the circadian clock. Light at dusk delays the clock. Light at dawn advances the clock. The threshold for human entrainment requires relatively bright light for a long duration, but the precise irradiance/duration relationships for photoentrainment have yet to be fully defined. Photoentrainment is achieved by a network of photosensitive retinal ganglion cells (pRGCs) which utilise the short-wavelength light-sensitive photopigment, melanopsin. Although rods and cones are not required, they do play a role in photoentrainment, by projecting to and modulating the endogenous photosensitivity of the pRGCs, but in a manner that remains poorly understood. It is also important to emphasise that the age and prior light exposure of an individual will modify the efficacy of entrainment stimuli. Because of the complexity of photoreceptor interactions, attempts to develop evidence-based human centric lighting are not straightforward. We need to study how humans respond to dynamic light exposure in the ‘real world’ where light intensity, duration, spectral quality and the time of exposure vary greatly. Defining these parameters will allow the development of electric lighting systems that will enhance human circadian entrainment.

黎明和黄昏的光线是生物钟夹带的关键信号。黄昏的光线延迟了时钟。黎明的曙光使时钟提前。人体夹带的阈值需要长时间相对明亮的光，但光夹带的精确辐照度/持续时间关系尚未完全确定。光夹带是通过光敏视网膜神经节细胞 (pRGC) 网络实现的，该网络利用短波长光敏光色素黑视素。尽管杆和锥不是必需的，但它们确实通过投射和调节 pRGC 的内源性光敏性在光夹带中发挥作用，但其方式仍知之甚少。同样重要的是要强调个人的年龄和先前的光照会改变夹带刺激的功效。由于光感受器相互作用的复杂性，尝试开发以证据为基础的以人为本的照明并不简单。我们需要研究人类如何在“现实世界”中对动态光暴露做出反应，其中光强度、持续时间、光谱质量和暴露时间差异很大。定义这些参数将允许开发能够增强人类昼夜节律的电照明系统。