16 JULY/AUGUST 2017 LEDsmagazine.com
just on street
lighting with accepted accounting
for reflectance off street-level surfaces. But it did not consider buildings that might cause additional
uplight via reflections or indeed
other sources of uplight, such as
indoor spill, that is often prevalent
in urban areas.
The DOE project relied largely on
the SkyGlow Simulator model that
has been widely used in the astronomical community, and that was
developed by Miroslav Kocifaj from
the Slovak Academy of Sciences.
The work relied on approximately
200,000 computer runs that generated the results. The methodology centered
around sets of tests evaluating one variable
while other characteristics were kept constant. The modeling assumed ground reflectivity of 15% — a value commonly used in
atmospheric modeling. Four levels of uplight
were considered and two levels of lumen output. Perhaps the most significant variable
was spectral power distribution (SPD) where
ten SPDs from typical street-light products
The model returns sky glow impact on the
horizontal plane of an observer in terms of
diffuse irradiance or scotopic lux (lx). And
the DOE has reported the results of the
unweighted radiant power and the scoto-
pically-weighted sky glow. Conditions for a
near observer located at the edge of a typi-
cal city were reported along with those from
a far observer located 40 km from the cen-
ter of the city.
The results fill pages in the report as you
may expect, but here is the summary. In the
unweighted case, LED street lights reduce
sky glow at the near and far observers rela-
tive to all legacy products. In the unweighted
tests, the results depend on the specific
sources tested. The LEDs produce as lit-
tle as 20% of the legacy baseline and as
much as 160%. When measured at 40
km, the uplight characteristics of the
LED products, with uplight curtailed
by optics that direct the beam down-
ward, reduce the contribution of street
lights to sky glow by 95%.
The DOE did note that the industry can do better moving forward. For
example, specifiers can choose LED
street lights with SPDs that have less
short-wavelength energy. And remember that SPD and CCT are not equivalent metrics. As we have reported,
there has been a swell of public opinion, and even a recommendation by the
American Medical Association (AMA), to
limit CCT to 3000K or warmer (http://bit.
ly/2eW91WB). The DOE report states that
a lower CCT doesn’t always deliver a preferred SPD. And good lighting design practices that minimize the number of fixtures
installed along with autonomous dimming
can be far more valuable than CCT limits
in reducing sky glow and assuring healthy
lighting for humans. You can peruse the
full DOE report on the agency’s SSL website
DOE from page 15
Photo credit: NASA Earth Observatory image – Joshua Stevens; Suomi NPP VIIRS
data – Miguel Román, NASA’s Goddard Space Flight Center.
National Academy of Sciences reports on the state of LED and OLED lighting
The US National Academy of Sciences, Engineering, and Medicine
(NAS) has issued its second report on LED- and OLED-based lighting entitled “Assessment of Solid-State Lighting, Phase Two.” The
report projects that adoption of SSL can deliver a 40% reduction in
the amount of energy used for lighting by 2030. Moreover, the report
suggests that the US DOE SSL program has been a key element in a
faster-than-originally-predicted transition to LEDs and further suggests that the R&D funding by the agency should continue.
NAS issued its first report of SSL back in 2013 ( http://bit.ly/2u0n-
QmS). The reports are intended to inform the US Congress of progress
in SSL and are required under the Energy Independence and Security
Act (EISA) of 2007. The 2013 report urged continued research into core
LED and OLED technology to both improve efficacy and yield. And the
DOE has funded many such R&D programs, for example, through the
Small Business Innovation Research (SBIR) and Small Business Technology Transfer (ST TR) programs. We reported earlier this year on fiscal year 2017 grants ( http://bit.ly/2tVaast).
The DOE has also funded research at major players in the SSL
space, generally with the companies involved also committing
matching research dollars to the project. In mid-2015, for exam-
ple, the DOE awarded $10 million to nine companies and research
institutions ( http://bit.ly/1K19h24).
The new NAS report notes that SSL penetration has increased dramatically since the prior report, although in absolute numbers the
reach is still low. The research said that in 2015, only 6.4% of installed
general illumination in the US was based on SSL sources. The report
projects that number to reach 48% by 2020.
The report documents two side effects of the great interest in LEDs
that were not predicted in the 2013 report, and one has been a negative with the other very much a positive. The prior research did not
foresee the collapse in LED component prices due in part by oversupply, that caused what the NAS termed a “dramatic dislocation and
restructuring of the SSL marketplace.” In simple terms, players in the
SSL space have not made the profits that may have been expected. We
detailed the price collapse in coverage of Strategies in Light talks in
2016 ( http://bit.ly/1Y8jcbe).
The emerging positive side effect is the new applications now
being envisioned for SSL. For example, we have regularly covered
horticultural lighting and have another upcoming event focused
on the topic ( http://bit.ly/2sOpR5v). And other examples include
human-centric lighting (HCL), as well as smart lighting and the Io T.
The NAS report recommends specific investments it would