Too much “blue light”
National Lighting Bureau: The American Medical Association (AMA) recommendations on street lighting are based on the wrong metric.
The American Medical Association has issued flawed recommendations on the production of “blue light” by street lighting at night. It based them on measurements that, however, overlooked a specific type of “blue light”. According to spokespeople for the National Lighting Bureau, transport officials and other sectors believe (unfortunately mistakenly) that the AMA recommendations will help them reduce harmful effects on human health and the risk of accidents caused by poorly chosen lighting. Yet it is precisely “thanks to” these AMA statements that public safety on roads and city streets is compromised – pedestrians and drivers are not sufficiently visible, the lighting causes glare and often fails to provide visual comfort. Energy efficiency is also low in many cases (energy costs are higher than they need to be).
Is “blue light” harmful?
Randy Reid (editor and publisher of EdisonReport – one of the largest portals covering news in lighting technology) led a session at the Annual Lighting Forum entitled “Outdoor lighting and the AMA”, in which other lighting experts also spoke. Together they acknowledged that blue light affects circadian rhythms, but agreed that the AMA based its recommendations on the wrong metric – colour temperature instead of the melanopic content of light – and did not take the timing or intensity of lighting into account. “Blue light” affects people’s circadian rhythms. The cycles of wakefulness and sleep change, and over time the influence of this light also has a negative impact on human health.
When recommendations do more harm than good
According to the experts, the fundamental flaw in the recommendations is the very fact that the AMA defined “blue light” incorrectly. “Blue light” is not homogeneous; it has various components that need to be distinguished. The AMA focused on measuring only one type of “blue light” and overlooked its other components.
“Melanopic light” is a specific component produced by light sources. It can suppress the production of melatonin (a lack of this hormone causes general weakening of the body, insomnia and metabolic disorders). The AMA, however, did not take this component into account. Instead, it used CCT (also called chromaticity, colour temperature or correlated colour temperature) to indicate how much “blue light” an LED luminaire emits. However, CCT does not include “melanopic light”. It describes the colour of light as we perceive it visually, measured in kelvins. We often refer to it as “warm white”, “cool white” and so on. Different LED light sources emitting 3,000 K (the colour temperature recommended by the AMA for outdoor lighting) can, however, produce different amounts of “melanopic light”.
The specific “dose of blue light” is another important variable which the AMA also failed to determine correctly. This “dose” of light expresses the total amount of light energy that reaches the eye. It depends on the light intensity, the spectral composition, the duration and even on when we receive the “dose” of light – for example at night or in the morning. One cannot simply claim that a luminous flux is harmful because it is blue or contains blue wavelengths. It is necessary to know when and to what extent blue wavelengths reach the eye. For example, our bodies are programmed to expect high levels of certain blue wavelengths in the morning. They have a beneficial effect on us and help us “reset” our daily clock.
The AMA recommended 3,000 K for road and street lighting. According to Randy Reid, the publication of the AMA report led some cities to suspend their street lighting replacement programmes, while others switched to the 3,000 K recommended by the AMA. “We have found that road lighting at 4,100 K can provide up to 20 % better visual acuity than 3,000 K.”
Unfortunately, the AMA recommendations point street lighting designers in the wrong direction and have a negative impact on public safety and human health. They should be a helpful tool, but they are not.
