Brodrick posting November 22 - EERE

Postings: from the
desk of Jim Brodrick
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.
As always, if you have questions or comments, you can reach me at
postings@lightingfacts.com.