BrainStuff Classics: What Causes Red Eye in Photos?

How can a camera's flash make your eyes glow red? Tune in to learn how it works -- and how to prevent it -- in this classic episode of BrainStuff.

Learn more about your ad-choices at https://www.iheartpodcastnetwork.com

See omnystudio.com/listener for privacy information.

Episode Transcript

Speaker 1 (00:02):
Welcome to brain Stuff from How Stuff Works. Hey, brain Stuff,
I'm Lauren vogel Bam, and today's episode is another brain
Stuff classic. What causes red eye in photos and how
can you prevent it? Our former host, Christian Sager has
the answers for you High brain Stuff. I'm Christian Sager,

(00:24):
and I'm here to talk to you about why people's
eyes sometimes appear red in photos. Horrible glowing red, the
glow of eyes that have peered into the abyss and
through which the abyss peers back. I'm just kidding. It's
it's just simply a reflection. Everything that you can see
is reflecting some amount of light. You can see my

(00:45):
shirt because it's reflecting wavelengths of light and absorbing the
other wavelengths. Black things like my soul or I guess
my pupils absorbed most of the light that hits them.
Most pupils look black because they're shadowy windows to the retina.
The retina is lined with a dark pigment melanin, to
promote light absorption that gives all the photosensitive cells in

(01:08):
the retina the best chance at catching the light coming
at them. The retina contains a lot of those photosensitive cells,
some one hundred and seven million of them, plus nerves
to carry messages from those cells back to the brain.
All that stuff needs blood to function, so the retina
is also dense with blood vessels. Red eye is just

(01:30):
a glimpse at those blood vessels. You see. Camera flashes
illuminate everything within their reach, including the blood vessels in
the retina. A camera with a built in flash will
have that flash pointed directly at the subject at the
speed of light. The flash bounces off the subject and
back to the lens. If the angle is just right,

(01:51):
you wind up looking like a minion of zul. Part
of the problem is that you're using a flash, you're
in dim light, meaning that you're sub objects. Irises will
be dilated with lots of retina showing. Traditional built in
flashes go off near simultaneously with the shutter way too
fast for your iris is to contract. That's why some

(02:13):
newer flashes go off twice, once right before the picture
snaps to make your eyes adjust, and then again to
illuminate the scene. You can also prevent red eye by
controlling the angle of the light. Use a separate flash
positioned a few feet away from the camera. And try
bouncing the light off a nearby surface instead of pointing
it directly at your subject. Today's episode was produced by

(02:39):
Tyler Clang and written by Me in the Way Back
for our YouTube series If you miss Christian you can
find him on his new pop culture podcast super Context.
And if you enjoy our show and want to support
us in return for some brainy house wears or people wears,
visit our online shop at te public dot com slash
brain staff. And of course, for more on this and

(02:59):
a lot of other bloody excellent topics, visit our home planet,
how stuff Works dot com. H