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Fireworks are usually reserved for celebrations like the Fourth of July, Guy Fawkes and New Year’s Eve… but there’s another occasion when you can see a wonderful world of color explode in front of your eyes. And that’s when you close them.
So why do we see colors with our eyes closed?
The Magic of Phosphenes
We see colors when our eyes receive and interpret light on different wavelengths of the color spectrum. So when your eyes are closed, you wouldn’t think there would be any light for your eyes to see. But there is, and from a surprising source — your eyes themselves! Yes, the atoms in your eyes emit particles of light called biophotons as part of their normal function. In daylight, this activity is far too faint to notice. But when your eyes are closed, they see their own light emission and interpret it as colored blobs known as phosphenes.
What Triggers Phosphenes?
The easiest way to trigger a light show inside your own head is to rub your eyes. When you do, the pressure stimulates the cells in your retina, releasing phosphenes. While phosphenes can also be stimulated by external means, like electromagnetic probes (which scientists use to study the phenomenon), they are most commonly caused by other forms of pressure on your eyes, like a particularly hard sneeze, a bump on the head, or standing up too fast.
Are Phosphenes Dangerous?
Most of the time, phosphenes are harmless. And in some cases, they are even considered desirable – people who meditate call them nimitta, the light of the mind. But in some cases, phosphenes may be a sign of a potentially serious medical condition. Phosphenes can be caused by radiation exposure or as a side effect of certain drugs. Phosphenes, particularly if they are triggered by sounds rather than pressure, are also a key symptom of optic neuritis, a condition associated with Multiple Sclerosis. If you have concerns about phosphenes, consult with your eye doctor.
Otherwise, just enjoy the light show. Because everyone could use a little more color in their lives.