Guest post by Jim Brodrick, Department of Energy
You may recall that not too long ago, there was some mention in the news media about possible negative health effects of exposure to street lighting. While not all of the stories were completely accurate, we thought we should investigate further, so that’s what DOE did.
At our fifth annual SSL Market Introduction Workshop, which was held in Philadelphia in July, we assembled a panel of experts on the subject to give us an update on what we know – and don’t know – about the health effects of exposure to light at night, focusing on the differences in spectra between available light source technologies. A white paper summarizing the findings of that panel is now available online, and is entitled “Light at Night: The Latest Science.”
The panel was composed of several respected experts in the field: Ronald Gibbons of Virginia Tech Transportation Institute, George Brainard of the Neurology Department at Jefferson Medical College, and Mariana Figueiro of the Lighting Research Center at Rensselaer Polytechnic Institute. What did they conclude? First and foremost, that more research is needed.
Based on the scientific studies that have been done to date, it’s unclear what changes, if any, should be made to current best-practice lighting design. For example, we now know that the light detected by our eyes doesn’t just enable us to see, it also helps to set our biological clock – or “circadian rhythm,” in scientific parlance. It does this through specialized cells called “intrinsically photosensitive retinal ganglion cells,” which were discovered just a few years ago and – mercifully – are known as ipRGCs for short. These ipRGCs are not involved in the visual process, but affect the body’s production of the hormone melatonin, which plays a key role in regulating circadian rhythm. There’s evidence that disrupting the circadian rhythm can cause health problems, and that short-wavelength (blue) light has a greater effect on melatonin production than light in other parts of the spectrum.
At this point in time we don’t know enough to determine how much nighttime light exposure it takes to affect health adversely. In fact, it appears that daytime light exposure – especially to light in the blue range – is something many of us could actually use more of to function at optimal efficiency, and may very well prove to be more significant in setting our biological clocks than exposure to light at night. One panelist recommended daytime light exposures be increased and enriched with short-wavelength (blue) visible radiation, while nighttime exposures be reduced and have less of a short-wavelength component.
But there’s also the matter of the effect of spectrum on visual performance. As another panelist reported, there’s evidence that broad-spectrum light sources (i.e., those featuring a substantial blue element) improve visibility over warmer-colored light sources in outdoor environments at night, even when those broad-spectrum light sources emit less photopic (i.e., “bright”) light. So phosphor-conversion LEDs, which currently operate most efficiently when producing cooler (bluer) light, have the potential to save a lot of energy while improving nighttime visibility and safety.
There’s no question that lighting design criteria should be sensitive to our biological needs as well as to our visual needs. But as you can see, right now the issue of street lighting’s effect on health is far from clear-cut, with many ramifications and nuances and a definite need for further research.
Just as we posted the white paper from the July workshop panel, along came a new report from a French agency, citing potential damage to the eyes from LEDs and other broad-spectrum light sources of high luminance. Some of you may have seen it or heard about it. It seems to be a review of the existing scientific literature on the topic. We’ll give it a careful look, just as we’ve been doing with the street lighting issue, to determine whether it warrants any change in the course that solid-state lighting has been on. If SSL is to achieve its potential, we can’t afford to have any preconceived notions – but neither can we afford to rush to judgment. Technology is driven by science, and science is based on facts and consensus interpretation, which take time and a lot of hard work.
