« on: Yesterday at 10:34:48 »
Quote from: David Cooper
I look to one side and gently press the corner of my eye on the opposite sideThese are phosphenes - seeing light when there is no light. They can be produced mechanically or electrically.
Quote from: stephencwll
When Iím in dark room, i know the room is dark but i see tens of thousands of tiny dots of various shades of grey or white.Your eyes have an enormous "dynamic range" - they can adapt from full sunlight to a moonless night.
There are a number of mechanisms that contribute to this range of sensitivity:
- The iris can open (dark night) or close down (bright sunlight)
- Switch from cones (bright colors in daylight), to rods (night, limited to black and white)
- Changing the concentration of enzymes in your rod cells
- The integration time can increase (like increasing the exposure time on a camera)
This is similar to the automatic gain control on an old analogue AM radio or analogue TV.
- When the signal is loud, the sound (radio) or image (TV) is clear
- When the signal is faint, the amplification is turned up to maximum, and the electrical interference is also amplified. Often the interference is as great as the signal.
It takes 10-30 minutes to adapt to the dark, if you are going to look at faint stars through a telescope.
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