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April 12

Blue sun

If you sit in the sun for a while, with your eyes closed, when you open your eyes, everything has a blue tinge to it. Why? — Preceding unsigned comment added by 95.180.195.181 (talk) 09:12, 12 April 2022 (UTC)[reply]

This subjective phenomenon is an instance of a more general process. If you gaze fixedly for 15 seconds or so at a well-illuminated image, not moving your eyes, and then quickly look at a white field, you'll see the "negative" image – not only does dark become light and vice versa, but colours turn into their complementary colours. Since your eyelids are reddish orange, while closed you see a fixed reddish orange field. After opening them, you see the bluish complement. Your colour vision process reduces the effect of what is constantly presented to your retina. In a room with "warm" yellowish light, once you get used to it, a white page looks white, not yellowish. See Colour constancy § Physiological basis. For an alternative theory, see Opponent process. --Lambiam 09:44, 12 April 2022 (UTC)[reply]

The missing link here is to afterimage. --184.144.97.125 (talk) 17:07, 12 April 2022 (UTC)[reply]

The effect is discussed in the sections Complementary colours § Afterimages and Afterimage § Negative afterimages. --Lambiam 13:06, 12 April 2022 (UTC)[reply]

Related to question: when I was a kid, I would press lightly on my closed eyes in the darkness when I was supposed to be sleeping. It would produce a pineapple yellow color, which would, depending on pressure and time, eventually turn into fractals. Viriditas (talk) 00:08, 14 April 2022 (UTC)[reply]

See the article Phosphene (not to be confused with Phosphine!). {The poster formerly known as 87.81.230.195} 90.200.65.249 (talk)