Sky & Telescope - July 2019 - 38

Orange You Glad?

Light Color vs. Ability
to Detect Nebulosity
LUMPS OF COAL Near the bright star Alpha Crucis (upper right) lie
dusty clouds that form part of the huge dark nebula called the Coalsack. Participants' ability to see the Coalsack and the nearby Small
Magellanic Cloud indicated their rod receptors' sensitivity.

J U LY 2 0 1 9 * S K Y & T E L E S C O P E

Number of participants

Coalsack
detected
1 minute
Coalsack
detail
detected
1 minute

0
Red

Orange

Green

White Bright red

Screen color
p RESULTS: ROD VISION Most observers could detect the Coalsack
Nebula after 1 minute, regardless of the screen color they'd been exposed to. But the number of participants who could detect detail in the
nebula varied noticeably with color.

ies - with slightly different design to remove the subjectivity
of star counting - is deﬁnitely warranted. In the meantime,
this study suggests that orange is the new red!

¢ DR. KEN WISHAW is a retired anesthesiologist and an
Honorary Senior Fellow and Adjunct Professor at the University of the Sunshine Coast, Queensland, Australia. He has a
post-graduate qualification in astronomy from the University of
Southern Queensland and is secretary of the Brisbane Astronomical Society. Contact him at kenwishaw@gmail.com.
Find the full research paper on the Brisbane Astronomical
Society's website: bas.asn.au.

COA LSACK: ESO / DIGITIZED SK Y SURV E Y 2 /
DAVIDE DE M A RTIN; G R A PH: THE AU THOR

Star charts are often drawn as light-colored detail on a
black background. The selection of black writing on a colored
background in this study was deliberate, in order to imitate
reading a star chart while also exceeding the colored light
exposure. It is reassuring that even after this overexposure,
the impaired dark adaptation recovers relatively quickly. Still,
if observers are required to reference a star chart frequently,
then they should optimize the color and brightness of the
light used.
It was likely that in a test of 15 subjects that there would
be one or two people with a high ratio of green cone receptors. Such people would likely need substantially dimmer
orange screens than red screens. While most people selected
orange at around two-thirds the brightness of red, two people
needed less than one-third the brightness of orange than red.
So there could be signiﬁcant personal variation; each astronomer needs to ﬁnd what is right for them.
Based on the data, I agree with Dick that orange, rather
than red, may be the optimal color for area and chart lighting. While not sufﬁciently different to warrant astronomers
going out and replacing their existing red lighting, the result
suggests that new area and chart lighting would best be done
in orange. It is also consistent with the International DarkSky Association's recommendation to light pedestrian areas
with orange-rich, rather than blue-rich, light, not only to
minimize light pollution but also to maximize our ability to
see into shadows outside the lit area.
Given the ramiﬁcations of this ﬁnding on many different
people who work in low-light-level environments, larger stud-

http://www.bas.asn.au

Sky & Telescope - July 2019

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