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Speaker 1: Welcome to brain Stuff from How Stuff Works. Hey, brain Stuff,

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Speaker 1: I'm Lauren vogel Bam, and today's episode is another brain

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Speaker 1: Stuff classic. What causes red eye in photos and how

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Speaker 1: can you prevent it? Our former host, Christian Sager has

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Speaker 1: the answers for you High brain Stuff. I'm Christian Sager,

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Speaker 1: and I'm here to talk to you about why people's

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Speaker 1: eyes sometimes appear red in photos. Horrible glowing red, the

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Speaker 1: glow of eyes that have peered into the abyss and

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Speaker 1: through which the abyss peers back. I'm just kidding. It's

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Speaker 1: it's just simply a reflection. Everything that you can see

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Speaker 1: is reflecting some amount of light. You can see my

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Speaker 1: shirt because it's reflecting wavelengths of light and absorbing the

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Speaker 1: other wavelengths. Black things like my soul or I guess

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Speaker 1: my pupils absorbed most of the light that hits them.

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Speaker 1: Most pupils look black because they're shadowy windows to the retina.

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Speaker 1: The retina is lined with a dark pigment melanin, to

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Speaker 1: promote light absorption that gives all the photosensitive cells in

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Speaker 1: the retina the best chance at catching the light coming

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Speaker 1: at them. The retina contains a lot of those photosensitive cells,

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Speaker 1: some one hundred and seven million of them, plus nerves

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Speaker 1: to carry messages from those cells back to the brain.

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Speaker 1: All that stuff needs blood to function, so the retina

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Speaker 1: is also dense with blood vessels. Red eye is just

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Speaker 1: a glimpse at those blood vessels. You see. Camera flashes

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Speaker 1: illuminate everything within their reach, including the blood vessels in

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Speaker 1: the retina. A camera with a built in flash will

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Speaker 1: have that flash pointed directly at the subject at the

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Speaker 1: speed of light. The flash bounces off the subject and

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Speaker 1: back to the lens. If the angle is just right,

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Speaker 1: you wind up looking like a minion of zul. Part

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Speaker 1: of the problem is that you're using a flash, you're

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Speaker 1: in dim light, meaning that you're sub objects. Irises will

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Speaker 1: be dilated with lots of retina showing. Traditional built in

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Speaker 1: flashes go off near simultaneously with the shutter way too

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Speaker 1: fast for your iris is to contract. That's why some

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Speaker 1: newer flashes go off twice, once right before the picture

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Speaker 1: snaps to make your eyes adjust, and then again to

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Speaker 1: illuminate the scene. You can also prevent red eye by

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Speaker 1: controlling the angle of the light. Use a separate flash

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Speaker 1: positioned a few feet away from the camera. And try

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Speaker 1: bouncing the light off a nearby surface instead of pointing

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Speaker 1: it directly at your subject. Today's episode was produced by

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Speaker 1: Tyler Clang and written by Me in the Way Back

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Speaker 1: for our YouTube series If you miss Christian you can

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Speaker 1: find him on his new pop culture podcast super Context.

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Speaker 1: And if you enjoy our show and want to support

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Speaker 1: us in return for some brainy house wears or people wears,

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Speaker 1: visit our online shop at te public dot com slash

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Speaker 1: brain staff. And of course, for more on this and

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Speaker 1: a lot of other bloody excellent topics, visit our home planet,

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Speaker 1: how stuff Works dot com. H