Sky & Telescope - July 2024 - 72

ASTRONOMER'S WORKBENCH by Jerry Oltion
Give Amber a Try
Preserve your night vision with a better flashlight.
MOST AMATEUR ASTRONOMERS use
red flashlights to preserve their night
vision. One of my very first columns
(S&T: July 2016, p. 72) was about making
your own variable-intensity red
flashlight, but that project was already
obsolete by the time my column came
out, because in the preceding issue
was an excellent article by Robert Dick
explaining why amber was a better
choice than red (S&T: June 2016, p. 22).
The cone cells in our eyes are much
more sensitive to amber than to red
light, so we don't need as much of it
to illuminate charts, eyepiece barrels,
etc. The result is less overall intensity
to wash out the rod cells responsible for
night vision.
You can buy amber flashlights, but
they all tend to be too bright. What we
need is a variable-intensity amber light
that dims down enough to be useful to
fully dark-adapted eyes. So I set out to
make one.
The biggest problem I encounter
when making a flashlight is figuring
out what to put the electronics in. My
first red one used the handle of an old
battery-operated fan, and my second
one was just a potentiometer stuck to
72 JULY 2024 * SKY & TELESCOPE
the outside of a cheap LED flashlight,
but this time I wanted something a
little more elegant. I needed a box that
would let me arrange the components
in an orderly fashion yet would look at
least reasonably decent when finished.
Fortunately, " project boxes " are
made for exactly this sort of thing, and
there are a bewildering variety of them
available at electronics stores, hobby
shops, and online. They're made of ABS
plastic, so they're easy to drill, file, glue,
and screw into.
I measured the components I
intended to use and came up with a layout
that would require roughly 2.75″ by
1.5″ by 1″ (70 mm by 38 mm by 25 mm)
of interior space. So I ordered a box that
was advertised as 2.83″ by 1.65″ by 0.91″
outside dimensions. That was almost
too small! I made it work, but it was
tight. If you try this, you might want to
give yourself a little more wiggle room.
(But bear in mind that you don't want
it too big or you can't hold it in your
The switch and brightness control are
positioned in convenient spots to reach with a
thumb. The light doesn't look like much by day,
but it's plenty bright at night . . . and can be
dimmed down to whatever level you want.
pLeft: Here are all the components for the
flashlight: the project box, the battery holder,
a 1K pot, a 75-ohm fixed resistor, a rocker
switch, and a bright amber LED. Note the holes
cut in the box to accommodate the switch and
the potentiometer. Right: The components
made a tight fit. The battery holder worked best
upside down, so I crafted a little handle to lift
it out when the batteries need replacing, which
won't be often. I figure it'll take about 250
hours of use at half brightness.
teeth, a must for a truly useful astroflashlight!)
The
components are simple: a battery
holder for two AAA batteries, a
1- or 2-kilohm variable resistor (called
a potentiometer or just a " pot " ), a
75-ohm fixed resistor, a switch, and a
ALL IMAGES COURTESY OF THE AUTHOR
Sky & Telescope - July 2024

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