The red-eye effect in Photography is the common appearance of red eyes on photographs taken with a photographic flash when the flash is too close to the lens (as with most compact cameras).

You’ve seen the dreaded demon-eye effect that occurs when the camera flash bounces off the eye of a person or pet. An otherwise wonderful picture can be ruined by this. Technically, this is called red-eye and is caused when the pupil of your subject’s eye is wide open and the light from the camera’s flash reflects off the subjects retina. In people, the color ends up red; in pets, the color is often green.

The effect is generally more pronounced in people with grey or blue eyes and in children. This is because pale irises have less melanin in them and so allow more light to pass through to the retina. Children, despite superficial appearances, do not have larger pupils but their pupils are more reactive to light and are able to open to the fullest extent in low light conditions.

Many photo editing programs include a red-eye correction filter, but this may not allow your photograph subject to appear normal. These filters also do not work on the green effect produced in a pet’s eyes. Photo stores sell pens that are used to clear up red-eye, but again they are not always natural-looking and do not work on the green. The best thing is to prevent the demon-eye effect from the start.

It is rare to find a digital camera that does not come with a red-eye reduction feature. This feature can be turned off or on. It is best left on in all circumstances other than direct sunlight. The red-eye reduction feature works by flashing a short burst of light at your subject before you snap the picture. This burst of light causes the subject’s pupil to close and makes it less likely for the camera’s flash to reflect off the retina. This in turn reduces the chance of red-eye.

It also helps to direct the flash of your camera so it does not directly hit your subject’s eyes. Bouncing the flash off a nearby wall or other object will soften its effect and reduce the chances of this unwanted malady. Between bouncing the flash and using your digital camera’s red-eye reduction feature, your little angel, whether human or animal, will have eyes that don’t glow.

Professional photographers prefer to use ambient light or indirect flash as the red-eye reduction system does not always prevent red eyes, for example if people look away during the pre-flash. In any case, people with small pupils do not look natural on photographs. Many people also find the pre-flashes annoying. By coincidence, lighting which produces red-eye effect is also believed to produce very unflattering photographs; hard and flat lighting is considered something to avoid.

Probably the best tip is to have the subject not look straight at the camera, instead look at the shoulder of the photographer. That's why many portrait photographers will hold a toy or doll at arms length just prior to taking a phot of a child. In this way they get a natural pose and reduce the red-eye effect.