Concerns about LED street lights and blue light came to the fore in the public consciousness following the AMA guidance on street lighting that was issued in June of 2016. This is picked up by the general media, and this really captured the public's imagination. From the lighting community's perspective, and this includes our own, we felt that this guidance, while it was well-meaning, neglected to mention a number of very important factors. And these are things that, for example, directly impact the amount of short wavelengths that might be present to an individual. And from there, what the typical exposure level might be from those wavelengths to an individual. And then, from there, to the response that they might experience as a result.

None of these factors are unique to LED. There's no inherent difference between light coming from LEDs and light coming from any other source at the same wavelength and intensity. The issues that are being raised could just as easily apply to incandescent, or fluorescent, or metal halide, or other lighting sources. The term blue light is really being used as shorthand for a whole range of shorter wavelengths. So we've seen it used for anything from, say, mid green, maybe 530 nanometers, all the way down to something below 400 nanometers, which is well into the violet range.

The presence of these wavelengths at night can lead to potential disruption of the circadian clock of an individual, which the medical research community suggests can lead to things like sleepiness during the day, depression, and over eating, among other kinds of impacts. On a more serious note, these short wavelengths have the capability of suppressing their production of melatonin from the pineal gland in the brain. Melatonin has been shown to have cancer inhibiting properties.

The medical research community suggests the suppression of melatonin may be affecting the body's ability to stifle the growth of cancer cells during the time that that melatonin is being suppressed. First, I want to say that I am not a health professional. My expertise is in lighting. However, the concerns that have been identified were found in a laboratory context, often using non-human subjects, such as modified mice, rather than human subjects. So the extent to which these apply to a human situation, such as a small amount of light filtering through someone's bedroom window, have yet to be established.

The factors that contribute to potential health concerns, the first is spectral content for sure. Humans are definitely more sensitive to certain wavelengths than others. Also, and equally as important, are things like the intensity of the light that they're exposed to, the length of that exposure, and the timing of that exposure in that individual's 24 hour circadian clock. And then there are more difficult to predict factors such as how much light has that individual been exposed to during the previous 24 hour period. In our modern society, we spend a lot of time indoors, sometimes all day, right.

The lighting research center has actually made a point that the real issue here may be our lack of exposure during the normal day instead of exposure to some very small levels of light filtering in through a bedroom window. Numerous other factors also influence a general susceptibility of an individual, like their health overall, as well as engagement in other activities that also affect the quality of sleep, such as watching television or checking their social media, or consumption of alcohol before bed time. So this has been a major focus of the criticism of the guidance from the very beginning. Any one of these factors is a fairly easy target by itself. But the reality is actually a much more complex collection of all of these factors.

The lighting community feels that this complexity has been glossed over in the guidance, in favor of a more sound bite type of messaging. The impact of light on human health and the environment are rapidly growing research areas. And there's still a lot that we don't know. The DOE Solid-State Lighting Program is, therefore, following the research on these topics and engaging with medical and other experts to better understand the various impacts, including things like light spectrum, exposure duration, intensity, and other relevant factors.