4 ms·

> Animal eyes and brains are wired to control for the amount of ambient light. That’s why an apple looks red whether it is in the sun or the shade, even though

> Animal eyes and brains are wired to control for the amount of ambient light. That’s why an apple looks red whether it is in the sun or the shade, even though the wavelength hitting our eyes is quite different in those scenarios. It's not obvious to me why the wavelength should be different when an apple is viewed in direct sunlight vs indirect sunlight (shade). Dimmer, lower amplitude, but different wavelength?

thfuran 9y ago
Maybe with less direct light, more of the light is made up of light reflected from surroundings, which quite likely has a different spectral power distribution than direct sunlight.
- jjoonathan 9y ago
  E.g. many shadows are blue-tinted because they are lit by the non-sun parts of the sky which are blue because Rayleigh scattering is stronger at short wavelengths.
- vvanders 9y ago
  There's also polarization to throw in the mix. Usually photographers will use a circular polarizer to remove reflections(say from water) while keeping much of the diffuse lighting intact.
dragonwriter 9y ago
> It's not obvious to me why the wavelength should be different when an apple is viewed in direct sunlight vs indirect sunlight (shade). Assuming all light is sourced from the sun, “shade” means the direct light is blocked and all light hitting the object is reflected from other objects. In most cases, that will mean that the incoming mix of wavelengths is different based on what objects in the environment reflect and where they are positioned and how they are lit (direct sun or shade, which makes this recursive). The difference in incoming mix of wavelengths will, for an object that doesn't reflect only a single wavelength, tend to result in a change in the relative intensities in the mix of outgoing wavelengths, which (if color perception didn't correct for illumination) will change the apparent color. And color perception doesn't completely correct for illumination, though it's usually good enough to associate the same object in daylight vs. shade; this lack of full correction is why lighting tricks can be used to create fairly radical changes in appearance. But those involve combinationsn of lighting differences and illuminated material that aren't common in nature, for the most part.
- amelius 9y ago
  But they are speaking of "the wavelength", i.e. they assume there is only a single wavelength. Your explanation throws away that simplifying assumption.

thfuran 9y ago

Maybe with less direct light, more of the light is made up of light reflected from surroundings, which quite likely has a different spectral power distribution than direct sunlight.

jjoonathan 9y ago
E.g. many shadows are blue-tinted because they are lit by the non-sun parts of the sky which are blue because Rayleigh scattering is stronger at short wavelengths.
vvanders 9y ago
There's also polarization to throw in the mix. Usually photographers will use a circular polarizer to remove reflections(say from water) while keeping much of the diffuse lighting intact.

dragonwriter 9y ago

> It's not obvious to me why the wavelength should be different when an apple is viewed in direct sunlight vs indirect sunlight (shade). Assuming all light is sourced from the sun, “shade” means the direct light is blocked and all light hitting the object is reflected from other objects. In most cases, that will mean that the incoming mix of wavelengths is different based on what objects in the environment reflect and where they are positioned and how they are lit (direct sun or shade, which makes this recursive). The difference in incoming mix of wavelengths will, for an object that doesn't reflect only a single wavelength, tend to result in a change in the relative intensities in the mix of outgoing wavelengths, which (if color perception didn't correct for illumination) will change the apparent color. And color perception doesn't completely correct for illumination, though it's usually good enough to associate the same object in daylight vs. shade; this lack of full correction is why lighting tricks can be used to create fairly radical changes in appearance. But those involve combinationsn of lighting differences and illuminated material that aren't common in nature, for the most part.

amelius 9y ago
But they are speaking of "the wavelength", i.e. they assume there is only a single wavelength. Your explanation throws away that simplifying assumption.