Two of my IES Color Committee friends and colleagues, Tony Esposito and Kevin Houser, have just published a paper in Scientific Reports that looks at the common assumption that CCT can be used to assess circadian entrainment and other biological impacts of light. The assumption by many is that high CCT light contains the blue wavelengths necessary for circadian entrainment, and that assumption is emphasized in the marketing a wide range of tunable white fixtures.
Their study used a five-channel LED system in a full scale model of a room. The LEDs were used to create over 200,000 SPDs across a range of color temperatures and illuminance levels. They found that CCT alone is not an accurate predictor of the spectral content of the light. Since the three major systems used to predict “biological potency” of light – CIE melanopic Equivalent Daylight Illuminance (mel-EDI), Equivalent Melanopic Lux (EML), and Circadian Stimulus (CS) – all use spectral analysis to understand biological impact, using CCT alone is simply inadequate. High CCT may correspond to circadian response, or it may not. They conclude their paper by saying
The lighting industry is experiencing rapid transformation as we expand our awareness of the non-visual impacts of light on humans. It is pertinent that we develop measures, methods, and strategies for implementing architectural lighting solutions that support these non-visual impacts. To do so, we need accurate and predictive measures of the biological potency of light that are based on sound science. In this study, we have argued that CCT is conceptually inappropriate for this purpose and performed a numerical analysis demonstrating that significant variation in circadian stimulus and melanopic equivalent daylight illuminance exists at any fixed CCT and photopic illuminance, making CCT an inappropriate proxy of those measures. Using CCT as a proxy for the biological potency of light cannot be justified.
Understanding that CCT doesn’t correspond with biological impact, it becomes important that designers understand the three systems and push manufacturers to begin providing the relevant information.
As interest in using light disinfection continues to grow standard setting organizations and manufacturers are becoming more active in this area. The International Commission on Illumination (CIE) has just released a position statement on the use of ultraviolet radiation to manage the risk of COVID-19 transmission.
Here are a few bullet points:
While ultraviolet light ranges from 400 nm to 100 nm, the most effective wavelengths are at around 254 nm and this is generally what is meant by germicidal ultraviolet or GUV.
UV-C has been successfully used for water disinfection and in air handling units for many years. UV-C has also seen a resurgence for use in healthcare environments.
Direct exposure to UV-C can cause photokeratitis (similar to snow blindness) and erythema (skin reddening similar to sunburn) so carefully shielded luminaires are required when used in occupied spaces.
Consumers should be wary of products not approved by consumer safety organizations. Such products could be hazardous to use or may not emit UV-C at all.
The position statement makes a couple of key points. The first is that the phrase itself “has been inaccurately used to represent the risk of actual eye damage and the influence on general well-being. The term ‘blue light hazard’ should only be used when considering the photochemical risk to the retinal tissues of the eye (technically referred to as “photomaculopathy”), usually associated with staring into bright sources, such as the sun or welding arcs”
The second point is that “There is no evidence in humans of any adverse health effects from occasional exposure to optical radiation at the exposure limits.” It’s an important position paper with links to research. Read it for yourself.
We’ve all heard about the effect blue light can have on our circadian rhythms. It can suppress the release of melatonin, which can delay sleep and reduce sleep quality with possible long-term health consequences. Circadian disruption has been associated with depression and increased risk of diseases such as diabetes, obesity and cancer.
Back in 2016 the AMA released a report recommending night-time outdoor lighting have a color temperature no higher than 3000 K to limit night-time exposure to blue light. That report was quickly criticized by the Lighting Research Center and the IES, among others, as I noted here and here. One of the key criticisms was that correlated color temperature is a poor measure of spectral content and says nothing about the amount of energy in the wavelength range that affects our circadian rhythms. A better measurement is melanopic content, which isn’t discussed in the report.
Last year Apple unveiled a feature in their OS and iOS called Night Shift. When enabled it causes the color of the display to become warmer in the evening. The assumption, the same as the AMA’s, is that warmer light has less blue so it won’t impact melatonin production.
A recently published paper in Lighting Research & Technology looked at the effectiveness of Night Shift. This preliminary study suggests that “changing the spectral composition of self-luminous displays without changing their brightness settings may be insufficient for preventing impacts on melatonin suppression.” Even when Night Shift was used, the devices still suppressed melatonin production. The authors noted that, “it is not known how this amount of suppression induces circadian disruption, delays sleep or affects health. Larger, more comprehensive epidemiological studies should investigate how the long-term use of these self-luminous displays affects people, especially adolescents and children.”
While additional studies are clearly needed, it provides additional evidence that lower CCT alone is probably not enough. With our display devices we should also lower the brightness.
Index crimes: 7% reduction in overall index crimes (day and night). This reduction in overall index crimes was driven by a 39% reduction in index crimes that took place outdoors at night.
Felony crimes: 5% reduction in overall felony crimes (day and night). This reduction in overall felony crimes was driven by a 30% reduction in felony crimes that took place outdoors at night.
Assault, homicide and weapons crimes: 2% reduction in overall assault, homicide, and weapons crimes (day and night). This reduction in overall assault, homicide and weapons crimes was driven by a 12% reduction in assault, homicide and weapons crimes that took place outdoors at night.
Misdemeanor crimes: No detectable change in net misdemeanor crimes in treatment communities.
The results of other studies have been mixed, but I’m not clear if they were controlled, randomized studies.
The disappointing thing, from a lighting designer’s perspective, is the data that’s missing. The report tells us the fixture wattage and lumen output, but doesn’t tell us the area covered or measure the increased light levels. Instead it treats light fixtures as fixed items and counts them per square block. This method would be fine if the world had only one type of outdoor fixture, but it doesn’t So more light is better, but it doesn’t say how much more or what the upper limit should be.
In the lighting community there was a considerable amount of frustration and anger over the report for several reasons. First, there were quite a few references cited that were either hearsay, such as a New York Times article about Brooklyn residents who didn’t like their new LED street lights, or were irrelevant, such as several articles about the effect of skyglow on nesting turtles. The other reason was that there was not a single lighting designer or researcher on the panel. Overall, it was a poorly researched paper that didn’t deserve the attention it received.
Shortly after it was issued, the Lighting Research Center at RPI issued a response paper. On March 15 the authors of that paper held a webinar to further address the AMA report. A video of that webinar is now available. If you’ve got an hour, take a look.
The key takeaways regarding the hazard of blue light from LEDs and the report are:
The criteria of blue light hazard for retinal damage is much more than just color temperature, and includes the source size, intensity per unit area on the retina, and SPD of the light source.
Disability glare is not a function of light source SPD, as the AMA paper suggests, although discomfort glare is. Short wavelengths increase discomfort glare.
Color temperature is the wrong measurement to determine whether or not a light source will affect the circadian system and melatonin production because color temperature does not provide complete SPD information. For example, some 3,000 K LEDs can have a greater impact than 4,000 K LEDs.
The criteria of blue light hazard for circadian disruption from a light source include – the intensity, duration of exposure, timing of exposure, and SPD.
News stories generated by the American Medical Association’s (AMA) community guidance on street lighting has elevated the topic of LED street lighting and its potential effects on health and the environment in the public’s mind. Discussions of these issues have many misperceptions and mischaracterizations of the technical information, and the difference between what has and hasn’t been scientifically established is often blurred.
DOE has assembled a variety of resources on the topic, to provide accurate, in-depth information that clarifies the current state of scientific understanding.
Almost as if on cue, Philips Lighting is hosting a webinar on light and health presented by Mariana Figuerro, the Light and Health Program Director at Lighting Research Center. I attended one of her in-person seminars earlier this year and I can say that she does a great job of explaining what aspects of light and health we can integrate into our practice now, and what aspects need additional research. You can read more about the webinar here, or go straight to the registration page here.