Speaker 1: I'm Kristin Conger and I'm Caroline Irvan, and we're hosts
Speaker 1: of the podcast Stuff Mom never told you that gets
Speaker 1: down to the business of being women from every imaginable angle.
Speaker 1: That's right. Kristen and I skillfully decode the biology, psychology,
Speaker 1: and sociology of ladies and gents from their evolutionary past
Speaker 1: a millennial present to better understand all of that stuff.
Speaker 1: Mom never told you. No offense moms, Now be sure
Speaker 1: to subscribe wherever you get your podcasts. Welcome to brain
Speaker 1: Stuff from How Stuff Works. Hi, brain Stuff, I'm Christian Sager,
Speaker 1: and I'm here to talk to you about why people's
Speaker 1: eyes sometimes appear red in photos. Horrible glowing red, the
Speaker 1: glow of eyes that have peered into the abyss and
Speaker 1: through which the abyss peers back. I'm just kidding. It's
Speaker 1: it's just simply a reflection. Everything that you can see
Speaker 1: is reflecting some amount of light. You can see my
Speaker 1: shirt because it's reflecting wavelengths of light and absorbing the
Speaker 1: other wavelengths. Black things like my soul or I guess
Speaker 1: my pupils absorb most of the light that hits them.
Speaker 1: Most pupils look black because they're shadowy windows to the retina.
Speaker 1: The retina is lined with a dark pigment melanin to
Speaker 1: promote light absorption. That gives all the photosensitive cells in
Speaker 1: the retina the best chance at catching the light coming
Speaker 1: at them. The retina contains a lot of those photosensitive cells,
Speaker 1: some one hundred and seven million of them, plus nerves
Speaker 1: to carry messages from those cells back to the brain.
Speaker 1: All that stuff needs blood to function, so the retina
Speaker 1: is also dense with blood vessels. Red eye is just
Speaker 1: a glimpse at those blood vessels. You see. Camera flashes
Speaker 1: illuminate everything within their reach, including the blood vessels in
Speaker 1: the retina. A camera with a built in flash will
Speaker 1: have that flash pointed direct at the subject at the
Speaker 1: speed of light. The flash bounces off the subject and
Speaker 1: back to the lens. If the angle is just right,
Speaker 1: you wind up looking like a minion of zool. Part
Speaker 1: of the problem is that you're using a flash you're
Speaker 1: in dim light, meaning that your subjects irises will be
Speaker 1: dilated with lots of retina showing. Traditional built in flashes
Speaker 1: go off near simultaneously with the shutter way too fast
Speaker 1: for your iris is to contract. That's why some newer
Speaker 1: flashes go off twice, once right before the picture snaps
Speaker 1: to make your eyes adjust, and then again to illuminate
Speaker 1: the scene. You can also prevent red eye by controlling
Speaker 1: the angle of the light. Use a separate flash positioned
Speaker 1: a few feet away from the camera, and try bouncing
Speaker 1: the light off a nearby surface instead of pointing it
Speaker 1: directly at your subject. Check out the brain stuff channel
Speaker 1: on YouTube, and for more on this and thousands of
Speaker 1: other topics, visit how stuff works dot com.