CIE Considers the "Good and Bad" of Light

The risks of being exposed to too much optical radiation from the sun have been known for thousands of years. People who stared at the sun suffered eye injuries. We also have natural aversion responses to very bright light. However, we need sufficient light to carry out our daily activities, ultraviolet radiation to enable our bodies to produce vitamin D and infrared radiation for warmth. Common sense has served us well for most of our evolution.

Until relatively recently, our daily lives were driven by the availability of optical radiation from the sun. We rose when sunlight appeared and sought shelter and sleep as the sun set, probably spending much of the day outdoors. The availability of artificial sources of light (and heat) allowed our ancestors to extend their activities into the evening. However, such light sources were not without risk. Flames, in their many forms, resulted in burns, fires and exposure to noxious fumes. These risks persist for significant numbers of people across the less-developed world.

The incandescent light bulb provided the first really reliable and lower risk source of light, but some risk remained - with up to 95% of the electrical energy being converted to heat instead of light. LED technology has provided a more energy-efficient solution to our lighting needs. However, many health concerns continue to be raised. CIE JTC 5 is currently revising the standard for the photobiological safety of lamps and lamp systems, and this work is nearing completion. The original standard (CIE S009/IEC 62471) defined risk groups and included short descriptors, which were open to misinterpretation. Most lamps and lamp systems are very unlikely to be harmful to people under reasonably foreseeable use. The exceptions are those that emit large amounts of ultraviolet radiation or which are primarily blue-light emitters. LED light sources that use a blue LED and a yellow phosphor will not exceed the blue light exposure limit under normal use exposure conditions. The revised standard is likely to emphasize that only Risk Group 3 lamps and lamp systems are of real concern. It is important that the harmful effects of a small number of optical radiation sources are addressed: this standard requires manufacturers to identify such sources to ensure that users are not at risk.

About the Role of Light for Biological Effects

Light has a significant role in determining our circadian rhythm, and achieves important biological effects that are distinct from perceptual vision. These effects are often referred to as non-image forming or nonvisual effects of light. Many non-visual effects of light are mediated via the eyes and are highly relevant for human health, performance and wellbeing.

These effects are:
• Each morning, light resets our biological clock, thus regulating the
24 hour patterns in our hormones and behavior, our sleep-wake
cycle and our circadian rhythm
• Light can improve alertness, alleviate seasonal and non-seasonal
depression and elicit fast responses in the pupillary reflex or in brain activity
• Too much light at night can disturb sleep and circadian rhythms,
but sufficient daytime light exposure can make us less vulnerable to
the adverse effects of light at night

The stimulation of ocular photoreceptors is essential to elicit the above-mentioned effects of light. The classic receptors for vision, the rods and cones, are relatively well understood and characterised. However, pioneering work over the last 25 years revealed that the eye has another kind of photoreceptor [1]. This photoreceptor has a peak sensitivity in the shorter wavelength part of the visible spectrum and plays an important role in non-visual effects of light. The photoreceptor is known as the ipRGC (intrinsically-photosensitive retinal ganglion cell), and its intrinsic photosensitivity is based on the photopigment melanopsin that is contained within these cells. Apart from their melanopsin-based photoreception, iPRGCs also receive input from the classic photoreceptors (i.e. rods and thee types of cone). In principle, all five photoreceptor types can contribute to non-visual responses to light, where the relative contribution of a single photoreceptor can vary depending on exposure properties such as the (retinal) irradiance, subjective time, light history, light adaptation or sleep pressure.

In 2013, CIE together with ZVEI supported a workshop, which brought together the world experts in the field and resulted in a paper [2], a CIE Technical Note [3] and has also been reflected in CEN/TR 16791:2017 [4]. The experts recognised that the sensors in the eye - the cones, rods and the newly discovered intrinsically-photosensitive retinal ganglion cells, all had a role in circadian rhythm entrainment, and possibly other wellbeing parameter.